Merge pull request #9175 from kprotty/thread

std.Thread enhancements

16 files changed, 878 insertions, 664 deletions

diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index 06fe2a84dc..91f7ff58c3 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -8,7 +8,11 @@
 //! primitives that operate on kernel threads. For concurrency primitives that support
 //! both evented I/O and async I/O, see the respective names in the top level std namespace.
 
-data: Data,
+const std = @import("std.zig");
+const os = std.os;
+const assert = std.debug.assert;
+const target = std.Target.current;
+const Atomic = std.atomic.Atomic;
 
 pub const AutoResetEvent = @import("Thread/AutoResetEvent.zig");
 pub const Futex = @import("Thread/Futex.zig");
@@ -18,117 +22,51 @@ pub const Mutex = @import("Thread/Mutex.zig");
 pub const Semaphore = @import("Thread/Semaphore.zig");
 pub const Condition = @import("Thread/Condition.zig");
 
-pub const use_pthreads = std.Target.current.os.tag != .windows and builtin.link_libc;
+pub const spinLoopHint = @compileError("deprecated: use std.atomic.spinLoopHint");
 
-const Thread = @This();
-const std = @import("std.zig");
-const builtin = std.builtin;
-const os = std.os;
-const mem = std.mem;
-const windows = std.os.windows;
-const c = std.c;
-const assert = std.debug.assert;
+pub const use_pthreads = target.os.tag != .windows and std.builtin.link_libc;
 
-const bad_startfn_ret = "expected return type of startFn to be 'u8', 'noreturn', 'void', or '!void'";
+const Thread = @This();
+const Impl = if (target.os.tag == .windows)
+    WindowsThreadImpl
+else if (use_pthreads)
+    PosixThreadImpl
+else if (target.os.tag == .linux)
+    LinuxThreadImpl
+else
+    UnsupportedImpl;
 
-/// Represents a kernel thread handle.
-/// May be an integer or a pointer depending on the platform.
-/// On Linux and POSIX, this is the same as Id.
-pub const Handle = if (use_pthreads)
-    c.pthread_t
-else switch (std.Target.current.os.tag) {
-    .linux => i32,
-    .windows => windows.HANDLE,
-    else => void,
-};
+impl: Impl,
 
 /// Represents a unique ID per thread.
-/// May be an integer or pointer depending on the platform.
-/// On Linux and POSIX, this is the same as Handle.
-pub const Id = switch (std.Target.current.os.tag) {
-    .windows => windows.DWORD,
-    else => Handle,
-};
+pub const Id = u64;
 
-pub const Data = if (use_pthreads)
-    struct {
-        handle: Thread.Handle,
-        memory: []u8,
-    }
-else switch (std.Target.current.os.tag) {
-    .linux => struct {
-        handle: Thread.Handle,
-        memory: []align(mem.page_size) u8,
-    },
-    .windows => struct {
-        handle: Thread.Handle,
-        alloc_start: *c_void,
-        heap_handle: windows.HANDLE,
-    },
-    else => struct {},
-};
-
-pub const spinLoopHint = @compileError("deprecated: use std.atomic.spinLoopHint");
-
-/// Returns the ID of the calling thread.
-/// Makes a syscall every time the function is called.
-/// On Linux and POSIX, this Id is the same as a Handle.
+/// Returns the platform ID of the callers thread.
+/// Attempts to use thread locals and avoid syscalls when possible.
 pub fn getCurrentId() Id {
-    if (use_pthreads) {
-        return c.pthread_self();
-    } else return switch (std.Target.current.os.tag) {
-        .linux => os.linux.gettid(),
-        .windows => windows.kernel32.GetCurrentThreadId(),
-        else => @compileError("Unsupported OS"),
-    };
+    return Impl.getCurrentId();
 }
 
-/// Returns the handle of this thread.
-/// On Linux and POSIX, this is the same as Id.
-/// On Linux, it is possible that the thread spawned with `spawn`
-/// finishes executing entirely before the clone syscall completes. In this
-/// case, this function will return 0 rather than the no-longer-existing thread's
-/// pid.
-pub fn handle(self: Thread) Handle {
-    return self.data.handle;
-}
+pub const CpuCountError = error{
+    PermissionDenied,
+    SystemResources,
+    Unexpected,
+};
 
-pub fn wait(self: *Thread) void {
-    if (use_pthreads) {
-        const err = c.pthread_join(self.data.handle, null);
-        switch (err) {
-            0 => {},
-            os.EINVAL => unreachable,
-            os.ESRCH => unreachable,
-            os.EDEADLK => unreachable,
-            else => unreachable,
-        }
-        std.heap.c_allocator.free(self.data.memory);
-        std.heap.c_allocator.destroy(self);
-    } else switch (std.Target.current.os.tag) {
-        .linux => {
-            while (true) {
-                const pid_value = @atomicLoad(i32, &self.data.handle, .SeqCst);
-                if (pid_value == 0) break;
-                const rc = os.linux.futex_wait(&self.data.handle, os.linux.FUTEX_WAIT, pid_value, null);
-                switch (os.linux.getErrno(rc)) {
-                    0 => continue,
-                    os.EINTR => continue,
-                    os.EAGAIN => continue,
-                    else => unreachable,
-                }
-            }
-            os.munmap(self.data.memory);
-        },
-        .windows => {
-            windows.WaitForSingleObjectEx(self.data.handle, windows.INFINITE, false) catch unreachable;
-            windows.CloseHandle(self.data.handle);
-            windows.HeapFree(self.data.heap_handle, 0, self.data.alloc_start);
-        },
-        else => @compileError("Unsupported OS"),
-    }
+/// Returns the platforms view on the number of logical CPU cores available.
+pub fn getCpuCount() CpuCountError!usize {
+    return Impl.getCpuCount();
 }
 
+/// Configuration options for hints on how to spawn threads.
+pub const SpawnConfig = struct {
+    // TODO compile-time call graph analysis to determine stack upper bound
+    // https://github.com/ziglang/zig/issues/157
+
+    /// Size in bytes of the Thread's stack
+    stack_size: usize = 16 * 1024 * 1024,
+};
+
 pub const SpawnError = error{
     /// A system-imposed limit on the number of threads was encountered.
     /// There are a number of limits that may trigger this error:
@@ -159,248 +97,552 @@ pub const SpawnError = error{
     Unexpected,
 };
 
-// Given `T`, the type of the thread startFn, extract the expected type for the
-// context parameter.
-fn SpawnContextType(comptime T: type) type {
-    const TI = @typeInfo(T);
-    if (TI != .Fn)
-        @compileError("expected function type, found " ++ @typeName(T));
+/// Spawns a new thread which executes `function` using `args` and returns a handle the spawned thread.
+/// `config` can be used as hints to the platform for now to spawn and execute the `function`.
+/// The caller must eventually either call `join()` to wait for the thread to finish and free its resources
+/// or call `detach()` to excuse the caller from calling `join()` and have the thread clean up its resources on completion`.
+pub fn spawn(config: SpawnConfig, comptime function: anytype, args: anytype) SpawnError!Thread {
+    if (std.builtin.single_threaded) {
+        @compileError("Cannot spawn thread when building in single-threaded mode");
+    }
+
+    const impl = try Impl.spawn(config, function, args);
+    return Thread{ .impl = impl };
+}
 
-    if (TI.Fn.args.len != 1)
-        @compileError("expected function with single argument, found " ++ @typeName(T));
+/// Represents a kernel thread handle.
+/// May be an integer or a pointer depending on the platform.
+pub const Handle = Impl.ThreadHandle;
 
-    return TI.Fn.args[0].arg_type orelse
-        @compileError("cannot use a generic function as thread startFn");
+/// Retrns the handle of this thread
+pub fn getHandle(self: Thread) Handle {
+    return self.impl.getHandle();
 }
 
-/// Spawns a new thread executing startFn, returning an handle for it.
-/// Caller must call wait on the returned thread.
-/// The `startFn` function must take a single argument of type T and return a
-/// value of type u8, noreturn, void or !void.
-/// The `context` parameter is of type T and is passed to the spawned thread.
-pub fn spawn(comptime startFn: anytype, context: SpawnContextType(@TypeOf(startFn))) SpawnError!*Thread {
-    if (builtin.single_threaded) @compileError("cannot spawn thread when building in single-threaded mode");
-    // TODO compile-time call graph analysis to determine stack upper bound
-    // https://github.com/ziglang/zig/issues/157
-    const default_stack_size = 16 * 1024 * 1024;
+/// Release the obligation of the caller to call `join()` and have the thread clean up its own resources on completion.
+/// Once called, this consumes the Thread object and invoking any other functions on it is considered undefined behavior.
+pub fn detach(self: Thread) void {
+    return self.impl.detach();
+}
 
-    const Context = @TypeOf(context);
+/// Waits for the thread to complete, then deallocates any resources created on `spawn()`.
+/// Once called, this consumes the Thread object and invoking any other functions on it is considered undefined behavior.
+pub fn join(self: Thread) void {
+    return self.impl.join();
+}
 
-    if (std.Target.current.os.tag == .windows) {
-        const WinThread = struct {
-            const OuterContext = struct {
-                thread: Thread,
-                inner: Context,
-            };
-            fn threadMain(raw_arg: windows.LPVOID) callconv(.C) windows.DWORD {
-                const arg = if (@sizeOf(Context) == 0) undefined //
-                else @ptrCast(*Context, @alignCast(@alignOf(Context), raw_arg)).*;
-
-                switch (@typeInfo(@typeInfo(@TypeOf(startFn)).Fn.return_type.?)) {
-                    .NoReturn => {
-                        startFn(arg);
-                    },
-                    .Void => {
-                        startFn(arg);
-                        return 0;
-                    },
-                    .Int => |info| {
-                        if (info.bits != 8) {
-                            @compileError(bad_startfn_ret);
-                        }
-                        return startFn(arg);
-                    },
-                    .ErrorUnion => |info| {
-                        if (info.payload != void) {
-                            @compileError(bad_startfn_ret);
-                        }
-                        startFn(arg) catch |err| {
-                            std.debug.warn("error: {s}\n", .{@errorName(err)});
-                            if (@errorReturnTrace()) |trace| {
-                                std.debug.dumpStackTrace(trace.*);
-                            }
-                        };
-                        return 0;
-                    },
-                    else => @compileError(bad_startfn_ret),
+/// State to synchronize detachment of spawner thread to spawned thread
+const Completion = Atomic(enum(u8) {
+    running,
+    detached,
+    completed,
+});
+
+/// Used by the Thread implementations to call the spawned function with the arguments.
+fn callFn(comptime f: anytype, args: anytype) switch (Impl) {
+    WindowsThreadImpl => std.os.windows.DWORD,
+    LinuxThreadImpl => u8,
+    PosixThreadImpl => ?*c_void,
+    else => unreachable,
+} {
+    const default_value = if (Impl == PosixThreadImpl) null else 0;
+    const bad_fn_ret = "expected return type of startFn to be 'u8', 'noreturn', 'void', or '!void'";
+
+    switch (@typeInfo(@typeInfo(@TypeOf(f)).Fn.return_type.?)) {
+        .NoReturn => {
+            @call(.{}, f, args);
+        },
+        .Void => {
+            @call(.{}, f, args);
+            return default_value;
+        },
+        .Int => |info| {
+            if (info.bits != 8) {
+                @compileError(bad_fn_ret);
+            }
+
+            const status = @call(.{}, f, args);
+            if (Impl != PosixThreadImpl) {
+                return status;
+            }
+
+            // pthreads don't support exit status, ignore value
+            _ = status;
+            return default_value;
+        },
+        .ErrorUnion => |info| {
+            if (info.payload != void) {
+                @compileError(bad_fn_ret);
+            }
+
+            @call(.{}, f, args) catch |err| {
+                std.debug.warn("error: {s}\n", .{@errorName(err)});
+                if (@errorReturnTrace()) |trace| {
+                    std.debug.dumpStackTrace(trace.*);
                 }
+            };
+
+            return default_value;
+        },
+        else => {
+            @compileError(bad_fn_ret);
+        },
+    }
+}
+
+/// We can't compile error in the `Impl` switch statement as its eagerly evaluated.
+/// So instead, we compile-error on the methods themselves for platforms which don't support threads.
+const UnsupportedImpl = struct {
+    pub const ThreadHandle = void;
+
+    fn getCurrentId() u64 {
+        return unsupported({});
+    }
+
+    fn getCpuCount() !usize {
+        return unsupported({});
+    }
+
+    fn spawn(config: SpawnConfig, comptime f: anytype, args: anytype) !Impl {
+        return unsupported(.{ config, f, args });
+    }
+
+    fn getHandle(self: Impl) ThreadHandle {
+        return unsupported(self);
+    }
+
+    fn detach(self: Impl) void {
+        return unsupported(self);
+    }
+
+    fn join(self: Impl) void {
+        return unsupported(self);
+    }
+
+    fn unsupported(unusued: anytype) noreturn {
+        @compileLog("Unsupported operating system", target.os.tag);
+        _ = unusued;
+        unreachable;
+    }
+};
+
+const WindowsThreadImpl = struct {
+    const windows = os.windows;
+
+    pub const ThreadHandle = windows.HANDLE;
+
+    fn getCurrentId() u64 {
+        return windows.kernel32.GetCurrentThreadId();
+    }
+
+    fn getCpuCount() !usize {
+        // Faster than calling into GetSystemInfo(), even if amortized.
+        return windows.peb().NumberOfProcessors;
+    }
+
+    thread: *ThreadCompletion,
+
+    const ThreadCompletion = struct {
+        completion: Completion,
+        heap_ptr: windows.PVOID,
+        heap_handle: windows.HANDLE,
+        thread_handle: windows.HANDLE = undefined,
+
+        fn free(self: ThreadCompletion) void {
+            const status = windows.kernel32.HeapFree(self.heap_handle, 0, self.heap_ptr);
+            assert(status != 0);
+        }
+    };
+
+    fn spawn(config: SpawnConfig, comptime f: anytype, args: anytype) !Impl {
+        const Args = @TypeOf(args);
+        const Instance = struct {
+            fn_args: Args,
+            thread: ThreadCompletion,
+
+            fn entryFn(raw_ptr: windows.PVOID) callconv(.C) windows.DWORD {
+                const self = @ptrCast(*@This(), @alignCast(@alignOf(@This()), raw_ptr));
+                defer switch (self.thread.completion.swap(.completed, .SeqCst)) {
+                    .running => {},
+                    .completed => unreachable,
+                    .detached => self.thread.free(),
+                };
+                return callFn(f, self.fn_args);
             }
         };
 
         const heap_handle = windows.kernel32.GetProcessHeap() orelse return error.OutOfMemory;
-        const byte_count = @alignOf(WinThread.OuterContext) + @sizeOf(WinThread.OuterContext);
-        const bytes_ptr = windows.kernel32.HeapAlloc(heap_handle, 0, byte_count) orelse return error.OutOfMemory;
-        errdefer assert(windows.kernel32.HeapFree(heap_handle, 0, bytes_ptr) != 0);
-        const bytes = @ptrCast([*]u8, bytes_ptr)[0..byte_count];
-        const outer_context = std.heap.FixedBufferAllocator.init(bytes).allocator.create(WinThread.OuterContext) catch unreachable;
-        outer_context.* = WinThread.OuterContext{
-            .thread = Thread{
-                .data = Thread.Data{
-                    .heap_handle = heap_handle,
-                    .alloc_start = bytes_ptr,
-                    .handle = undefined,
-                },
+        const alloc_bytes = @alignOf(Instance) + @sizeOf(Instance);
+        const alloc_ptr = windows.kernel32.HeapAlloc(heap_handle, 0, alloc_bytes) orelse return error.OutOfMemory;
+        errdefer assert(windows.kernel32.HeapFree(heap_handle, 0, alloc_ptr) != 0);
+
+        const instance_bytes = @ptrCast([*]u8, alloc_ptr)[0..alloc_bytes];
+        const instance = std.heap.FixedBufferAllocator.init(instance_bytes).allocator.create(Instance) catch unreachable;
+        instance.* = .{
+            .fn_args = args,
+            .thread = .{
+                .completion = Completion.init(.running),
+                .heap_ptr = alloc_ptr,
+                .heap_handle = heap_handle,
             },
-            .inner = context,
         };
 
-        const parameter = if (@sizeOf(Context) == 0) null else @ptrCast(*c_void, &outer_context.inner);
-        outer_context.thread.data.handle = windows.kernel32.CreateThread(null, default_stack_size, WinThread.threadMain, parameter, 0, null) orelse {
-            switch (windows.kernel32.GetLastError()) {
-                else => |err| return windows.unexpectedError(err),
-            }
+        // Windows appears to only support SYSTEM_INFO.dwAllocationGranularity minimum stack size.
+        // Going lower makes it default to that specified in the executable (~1mb).
+        // Its also fine if the limit here is incorrect as stack size is only a hint.
+        var stack_size = std.math.cast(u32, config.stack_size) catch std.math.maxInt(u32);
+        stack_size = std.math.max(64 * 1024, stack_size);
+
+        instance.thread.thread_handle = windows.kernel32.CreateThread(
+            null,
+            stack_size,
+            Instance.entryFn,
+            @ptrCast(*c_void, instance),
+            0,
+            null,
+        ) orelse {
+            const errno = windows.kernel32.GetLastError();
+            return windows.unexpectedError(errno);
         };
-        return &outer_context.thread;
+
+        return Impl{ .thread = &instance.thread };
     }
 
-    const MainFuncs = struct {
-        fn linuxThreadMain(ctx_addr: usize) callconv(.C) u8 {
-            const arg = if (@sizeOf(Context) == 0) undefined //
-            else @intToPtr(*Context, ctx_addr).*;
+    fn getHandle(self: Impl) ThreadHandle {
+        return self.thread.thread_handle;
+    }
 
-            switch (@typeInfo(@typeInfo(@TypeOf(startFn)).Fn.return_type.?)) {
-                .NoReturn => {
-                    startFn(arg);
-                },
-                .Void => {
-                    startFn(arg);
-                    return 0;
-                },
-                .Int => |info| {
-                    if (info.bits != 8) {
-                        @compileError(bad_startfn_ret);
-                    }
-                    return startFn(arg);
-                },
-                .ErrorUnion => |info| {
-                    if (info.payload != void) {
-                        @compileError(bad_startfn_ret);
-                    }
-                    startFn(arg) catch |err| {
-                        std.debug.warn("error: {s}\n", .{@errorName(err)});
-                        if (@errorReturnTrace()) |trace| {
-                            std.debug.dumpStackTrace(trace.*);
-                        }
-                    };
-                    return 0;
-                },
-                else => @compileError(bad_startfn_ret),
-            }
+    fn detach(self: Impl) void {
+        windows.CloseHandle(self.thread.thread_handle);
+        switch (self.thread.completion.swap(.detached, .SeqCst)) {
+            .running => {},
+            .completed => self.thread.free(),
+            .detached => unreachable,
         }
-        fn posixThreadMain(ctx: ?*c_void) callconv(.C) ?*c_void {
-            const arg = if (@sizeOf(Context) == 0) undefined //
-            else @ptrCast(*Context, @alignCast(@alignOf(Context), ctx)).*;
+    }
 
-            switch (@typeInfo(@typeInfo(@TypeOf(startFn)).Fn.return_type.?)) {
-                .NoReturn => {
-                    startFn(arg);
-                },
-                .Void => {
-                    startFn(arg);
-                    return null;
-                },
-                .Int => |info| {
-                    if (info.bits != 8) {
-                        @compileError(bad_startfn_ret);
-                    }
-                    // pthreads don't support exit status, ignore value
-                    _ = startFn(arg);
-                    return null;
-                },
-                .ErrorUnion => |info| {
-                    if (info.payload != void) {
-                        @compileError(bad_startfn_ret);
-                    }
-                    startFn(arg) catch |err| {
-                        std.debug.warn("error: {s}\n", .{@errorName(err)});
-                        if (@errorReturnTrace()) |trace| {
-                            std.debug.dumpStackTrace(trace.*);
-                        }
-                    };
-                    return null;
-                },
-                else => @compileError(bad_startfn_ret),
-            }
+    fn join(self: Impl) void {
+        windows.WaitForSingleObjectEx(self.thread.thread_handle, windows.INFINITE, false) catch unreachable;
+        windows.CloseHandle(self.thread.thread_handle);
+        assert(self.thread.completion.load(.SeqCst) == .completed);
+        self.thread.free();
+    }
+};
+
+const PosixThreadImpl = struct {
+    const c = std.c;
+
+    pub const ThreadHandle = c.pthread_t;
+
+    fn getCurrentId() Id {
+        switch (target.os.tag) {
+            .linux => {
+                return LinuxThreadImpl.getCurrentId();
+            },
+            .macos, .ios, .watchos, .tvos => {
+                var thread_id: u64 = undefined;
+                // Pass thread=null to get the current thread ID.
+                assert(c.pthread_threadid_np(null, &thread_id) == 0);
+                return thread_id;
+            },
+            .dragonfly => {
+                return @bitCast(u32, c.lwp_gettid());
+            },
+            .netbsd => {
+                return @bitCast(u32, c._lwp_self());
+            },
+            .freebsd => {
+                return @bitCast(u32, c.pthread_getthreadid_np());
+            },
+            .openbsd => {
+                return @bitCast(u32, c.getthrid());
+            },
+            .haiku => {
+                return @bitCast(u32, c.find_thread(null));
+            },
+            else => {
+                return @ptrToInt(c.pthread_self());
+            },
         }
-    };
+    }
+
+    fn getCpuCount() !usize {
+        switch (target.os.tag) {
+            .linux => {
+                return LinuxThreadImpl.getCpuCount();
+            },
+            .openbsd => {
+                var count: c_int = undefined;
+                var count_size: usize = @sizeOf(c_int);
+                const mib = [_]c_int{ os.CTL_HW, os.HW_NCPUONLINE };
+                os.sysctl(&mib, &count, &count_size, null, 0) catch |err| switch (err) {
+                    error.NameTooLong, error.UnknownName => unreachable,
+                    else => |e| return e,
+                };
+                return @intCast(usize, count);
+            },
+            .haiku => {
+                var count: u32 = undefined;
+                var system_info: os.system_info = undefined;
+                _ = os.system.get_system_info(&system_info); // always returns B_OK
+                count = system_info.cpu_count;
+                return @intCast(usize, count);
+            },
+            else => {
+                var count: c_int = undefined;
+                var count_len: usize = @sizeOf(c_int);
+                const name = if (comptime target.isDarwin()) "hw.logicalcpu" else "hw.ncpu";
+                os.sysctlbynameZ(name, &count, &count_len, null, 0) catch |err| switch (err) {
+                    error.NameTooLong, error.UnknownName => unreachable,
+                    else => |e| return e,
+                };
+                return @intCast(usize, count);
+            },
+        }
+    }
+
+    handle: ThreadHandle,
+
+    fn spawn(config: SpawnConfig, comptime f: anytype, args: anytype) !Impl {
+        const Args = @TypeOf(args);
+        const allocator = std.heap.c_allocator;
+
+        const Instance = struct {
+            fn entryFn(raw_arg: ?*c_void) callconv(.C) ?*c_void {
+                // @alignCast() below doesn't support zero-sized-types (ZST)
+                if (@sizeOf(Args) < 1) {
+                    return callFn(f, @as(Args, undefined));
+                }
+
+                const args_ptr = @ptrCast(*Args, @alignCast(@alignOf(Args), raw_arg));
+                defer allocator.destroy(args_ptr);
+                return callFn(f, args_ptr.*);
+            }
+        };
+
+        const args_ptr = try allocator.create(Args);
+        args_ptr.* = args;
+        errdefer allocator.destroy(args_ptr);
 
-    if (Thread.use_pthreads) {
         var attr: c.pthread_attr_t = undefined;
         if (c.pthread_attr_init(&attr) != 0) return error.SystemResources;
         defer assert(c.pthread_attr_destroy(&attr) == 0);
 
-        const thread_obj = try std.heap.c_allocator.create(Thread);
-        errdefer std.heap.c_allocator.destroy(thread_obj);
-        if (@sizeOf(Context) > 0) {
-            thread_obj.data.memory = try std.heap.c_allocator.allocAdvanced(
-                u8,
-                @alignOf(Context),
-                @sizeOf(Context),
-                .at_least,
-            );
-            errdefer std.heap.c_allocator.free(thread_obj.data.memory);
-            mem.copy(u8, thread_obj.data.memory, mem.asBytes(&context));
-        } else {
-            thread_obj.data.memory = @as([*]u8, undefined)[0..0];
-        }
-
         // Use the same set of parameters used by the libc-less impl.
-        assert(c.pthread_attr_setstacksize(&attr, default_stack_size) == 0);
-        assert(c.pthread_attr_setguardsize(&attr, mem.page_size) == 0);
+        const stack_size = std.math.max(config.stack_size, 16 * 1024);
+        assert(c.pthread_attr_setstacksize(&attr, stack_size) == 0);
+        assert(c.pthread_attr_setguardsize(&attr, std.mem.page_size) == 0);
 
-        const err = c.pthread_create(
-            &thread_obj.data.handle,
+        var handle: c.pthread_t = undefined;
+        switch (c.pthread_create(
+            &handle,
             &attr,
-            MainFuncs.posixThreadMain,
-            thread_obj.data.memory.ptr,
-        );
-        switch (err) {
-            0 => return thread_obj,
+            Instance.entryFn,
+            if (@sizeOf(Args) > 1) @ptrCast(*c_void, args_ptr) else undefined,
+        )) {
+            0 => return Impl{ .handle = handle },
             os.EAGAIN => return error.SystemResources,
             os.EPERM => unreachable,
             os.EINVAL => unreachable,
-            else => return os.unexpectedErrno(err),
+            else => |err| return os.unexpectedErrno(err),
+        }
+    }
+
+    fn getHandle(self: Impl) ThreadHandle {
+        return self.handle;
+    }
+
+    fn detach(self: Impl) void {
+        switch (c.pthread_detach(self.handle)) {
+            0 => {},
+            os.EINVAL => unreachable, // thread handle is not joinable
+            os.ESRCH => unreachable, // thread handle is invalid
+            else => unreachable,
+        }
+    }
+
+    fn join(self: Impl) void {
+        switch (c.pthread_join(self.handle, null)) {
+            0 => {},
+            os.EINVAL => unreachable, // thread handle is not joinable (or another thread is already joining in)
+            os.ESRCH => unreachable, // thread handle is invalid
+            os.EDEADLK => unreachable, // two threads tried to join each other
+            else => unreachable,
         }
+    }
+};
+
+const LinuxThreadImpl = struct {
+    const linux = os.linux;
 
-        return thread_obj;
+    pub const ThreadHandle = i32;
+
+    threadlocal var tls_thread_id: ?Id = null;
+
+    fn getCurrentId() Id {
+        return tls_thread_id orelse {
+            const tid = @bitCast(u32, linux.gettid());
+            tls_thread_id = tid;
+            return tid;
+        };
     }
 
-    var guard_end_offset: usize = undefined;
-    var stack_end_offset: usize = undefined;
-    var thread_start_offset: usize = undefined;
-    var context_start_offset: usize = undefined;
-    var tls_start_offset: usize = undefined;
-    const mmap_len = blk: {
-        var l: usize = mem.page_size;
-        // Allocate a guard page right after the end of the stack region
-        guard_end_offset = l;
-        // The stack itself, which grows downwards.
-        l = mem.alignForward(l + default_stack_size, mem.page_size);
-        stack_end_offset = l;
-        // Above the stack, so that it can be in the same mmap call, put the Thread object.
-        l = mem.alignForward(l, @alignOf(Thread));
-        thread_start_offset = l;
-        l += @sizeOf(Thread);
-        // Next, the Context object.
-        if (@sizeOf(Context) != 0) {
-            l = mem.alignForward(l, @alignOf(Context));
-            context_start_offset = l;
-            l += @sizeOf(Context);
+    fn getCpuCount() !usize {
+        const cpu_set = try os.sched_getaffinity(0);
+        // TODO: should not need this usize cast
+        return @as(usize, os.CPU_COUNT(cpu_set));
+    }
+
+    thread: *ThreadCompletion,
+
+    const ThreadCompletion = struct {
+        completion: Completion = Completion.init(.running),
+        child_tid: Atomic(i32) = Atomic(i32).init(1),
+        parent_tid: i32 = undefined,
+        mapped: []align(std.mem.page_size) u8,
+
+        /// Calls `munmap(mapped.ptr, mapped.len)` then `exit(1)` without touching the stack (which lives in `mapped.ptr`).
+        /// Ported over from musl libc's pthread detached implementation:
+        /// https://github.com/ifduyue/musl/search?q=__unmapself
+        fn freeAndExit(self: *ThreadCompletion) noreturn {
+            const unmap_and_exit: []const u8 = switch (target.cpu.arch) {
+                .i386 => (
+                    \\  movl $91, %%eax
+                    \\  movl %[ptr], %%ebx
+                    \\  movl %[len], %%ecx
+                    \\  int $128
+                    \\  movl $1, %%eax
+                    \\  movl $0, %%ebx
+                    \\  int $128
+                ),
+                .x86_64 => (
+                    \\  movq $11, %%rax
+                    \\  movq %[ptr], %%rbx
+                    \\  movq %[len], %%rcx
+                    \\  syscall
+                    \\  movq $60, %%rax
+                    \\  movq $1, %%rdi
+                    \\  syscall
+                ),
+                .arm, .armeb, .thumb, .thumbeb => (
+                    \\  mov r7, #91
+                    \\  mov r0, %[ptr]
+                    \\  mov r1, %[len]
+                    \\  svc 0
+                    \\  mov r7, #1
+                    \\  mov r0, #0
+                    \\  svc 0
+                ),
+                .aarch64, .aarch64_be, .aarch64_32 => (
+                    \\  mov x8, #215
+                    \\  mov x0, %[ptr]
+                    \\  mov x1, %[len]
+                    \\  svc 0
+                    \\  mov x8, #93
+                    \\  mov x0, #0
+                    \\  svc 0
+                ),
+                .mips, .mipsel => (
+                    \\  move $sp, $25
+                    \\  li $2, 4091
+                    \\  move $4, %[ptr]
+                    \\  move $5, %[len]
+                    \\  syscall
+                    \\  li $2, 4001
+                    \\  li $4, 0
+                    \\  syscall
+                ),
+                .mips64, .mips64el => (
+                    \\  li $2, 4091
+                    \\  move $4, %[ptr]
+                    \\  move $5, %[len]
+                    \\  syscall
+                    \\  li $2, 4001
+                    \\  li $4, 0
+                    \\  syscall
+                ),
+                .powerpc, .powerpcle, .powerpc64, .powerpc64le => (
+                    \\  li 0, 91
+                    \\  mr %[ptr], 3
+                    \\  mr %[len], 4
+                    \\  sc
+                    \\  li 0, 1
+                    \\  li 3, 0
+                    \\  sc
+                    \\  blr
+                ),
+                .riscv64 => (
+                    \\  li a7, 215
+                    \\  mv a0, %[ptr]
+                    \\  mv a1, %[len]
+                    \\  ecall
+                    \\  li a7, 93
+                    \\  mv a0, zero
+                    \\  ecall
+                ),
+                else => |cpu_arch| {
+                    @compileLog("Unsupported linux arch ", cpu_arch);
+                },
+            };
+
+            asm volatile (unmap_and_exit
+                :
+                : [ptr] "r" (@ptrToInt(self.mapped.ptr)),
+                  [len] "r" (self.mapped.len)
+                : "memory"
+            );
+
+            unreachable;
         }
-        // Finally, the Thread Local Storage, if any.
-        l = mem.alignForward(l, os.linux.tls.tls_image.alloc_align);
-        tls_start_offset = l;
-        l += os.linux.tls.tls_image.alloc_size;
-        // Round the size to the page size.
-        break :blk mem.alignForward(l, mem.page_size);
     };
 
-    const mmap_slice = mem: {
-        // Map the whole stack with no rw permissions to avoid
-        // committing the whole region right away
-        const mmap_slice = os.mmap(
+    fn spawn(config: SpawnConfig, comptime f: anytype, args: anytype) !Impl {
+        const Args = @TypeOf(args);
+        const Instance = struct {
+            fn_args: Args,
+            thread: ThreadCompletion,
+
+            fn entryFn(raw_arg: usize) callconv(.C) u8 {
+                const self = @intToPtr(*@This(), raw_arg);
+                defer switch (self.thread.completion.swap(.completed, .SeqCst)) {
+                    .running => {},
+                    .completed => unreachable,
+                    .detached => self.thread.freeAndExit(),
+                };
+                return callFn(f, self.fn_args);
+            }
+        };
+
+        var guard_offset: usize = undefined;
+        var stack_offset: usize = undefined;
+        var tls_offset: usize = undefined;
+        var instance_offset: usize = undefined;
+
+        const map_bytes = blk: {
+            var bytes: usize = std.mem.page_size;
+            guard_offset = bytes;
+
+            bytes += std.math.max(std.mem.page_size, config.stack_size);
+            bytes = std.mem.alignForward(bytes, std.mem.page_size);
+            stack_offset = bytes;
+
+            bytes = std.mem.alignForward(bytes, linux.tls.tls_image.alloc_align);
+            tls_offset = bytes;
+            bytes += linux.tls.tls_image.alloc_size;
+
+            bytes = std.mem.alignForward(bytes, @alignOf(Instance));
+            instance_offset = bytes;
+            bytes += @sizeOf(Instance);
+
+            bytes = std.mem.alignForward(bytes, std.mem.page_size);
+            break :blk bytes;
+        };
+
+        // map all memory needed without read/write permissions
+        // to avoid committing the whole region right away
+        const mapped = os.mmap(
             null,
-            mmap_len,
+            map_bytes,
             os.PROT_NONE,
             os.MAP_PRIVATE | os.MAP_ANONYMOUS,
             -1,
@@ -411,73 +653,57 @@ pub fn spawn(comptime startFn: anytype, context: SpawnContextType(@TypeOf(startF
             error.PermissionDenied => unreachable,
             else => |e| return e,
         };
-        errdefer os.munmap(mmap_slice);
+        assert(mapped.len >= map_bytes);
+        errdefer os.munmap(mapped);
 
-        // Map everything but the guard page as rw
+        // map everything but the guard page as read/write
         os.mprotect(
-            mmap_slice[guard_end_offset..],
+            mapped[guard_offset..],
             os.PROT_READ | os.PROT_WRITE,
         ) catch |err| switch (err) {
             error.AccessDenied => unreachable,
             else => |e| return e,
         };
 
-        break :mem mmap_slice;
-    };
-
-    const mmap_addr = @ptrToInt(mmap_slice.ptr);
-
-    const thread_ptr = @alignCast(@alignOf(Thread), @intToPtr(*Thread, mmap_addr + thread_start_offset));
-    thread_ptr.data.memory = mmap_slice;
+        // Prepare the TLS segment and prepare a user_desc struct when needed on i386
+        var tls_ptr = os.linux.tls.prepareTLS(mapped[tls_offset..]);
+        var user_desc: if (target.cpu.arch == .i386) os.linux.user_desc else void = undefined;
+        if (target.cpu.arch == .i386) {
+            defer tls_ptr = @ptrToInt(&user_desc);
+            user_desc = .{
+                .entry_number = os.linux.tls.tls_image.gdt_entry_number,
+                .base_addr = tls_ptr,
+                .limit = 0xfffff,
+                .seg_32bit = 1,
+                .contents = 0, // Data
+                .read_exec_only = 0,
+                .limit_in_pages = 1,
+                .seg_not_present = 0,
+                .useable = 1,
+            };
+        }
 
-    var arg: usize = undefined;
-    if (@sizeOf(Context) != 0) {
-        arg = mmap_addr + context_start_offset;
-        const context_ptr = @alignCast(@alignOf(Context), @intToPtr(*Context, arg));
-        context_ptr.* = context;
-    }
+        const instance = @ptrCast(*Instance, @alignCast(@alignOf(Instance), &mapped[instance_offset]));
+        instance.* = .{
+            .fn_args = args,
+            .thread = .{ .mapped = mapped },
+        };
 
-    if (std.Target.current.os.tag == .linux) {
-        const flags: u32 = os.CLONE_VM | os.CLONE_FS | os.CLONE_FILES |
-            os.CLONE_SIGHAND | os.CLONE_THREAD | os.CLONE_SYSVSEM |
+        const flags: u32 = os.CLONE_THREAD | os.CLONE_DETACHED |
+            os.CLONE_VM | os.CLONE_FS | os.CLONE_FILES |
             os.CLONE_PARENT_SETTID | os.CLONE_CHILD_CLEARTID |
-            os.CLONE_DETACHED | os.CLONE_SETTLS;
-        // This structure is only needed when targeting i386
-        var user_desc: if (std.Target.current.cpu.arch == .i386) os.linux.user_desc else void = undefined;
-
-        const tls_area = mmap_slice[tls_start_offset..];
-        const tp_value = os.linux.tls.prepareTLS(tls_area);
-
-        const newtls = blk: {
-            if (std.Target.current.cpu.arch == .i386) {
-                user_desc = os.linux.user_desc{
-                    .entry_number = os.linux.tls.tls_image.gdt_entry_number,
-                    .base_addr = tp_value,
-                    .limit = 0xfffff,
-                    .seg_32bit = 1,
-                    .contents = 0, // Data
-                    .read_exec_only = 0,
-                    .limit_in_pages = 1,
-                    .seg_not_present = 0,
-                    .useable = 1,
-                };
-                break :blk @ptrToInt(&user_desc);
-            } else {
-                break :blk tp_value;
-            }
-        };
+            os.CLONE_SIGHAND | os.CLONE_SYSVSEM | os.CLONE_SETTLS;
 
-        const rc = os.linux.clone(
-            MainFuncs.linuxThreadMain,
-            mmap_addr + stack_end_offset,
+        switch (linux.getErrno(linux.clone(
+            Instance.entryFn,
+            @ptrToInt(&mapped[stack_offset]),
             flags,
-            arg,
-            &thread_ptr.data.handle,
-            newtls,
-            &thread_ptr.data.handle,
-        );
-        switch (os.errno(rc)) {
-            0 => return thread_ptr,
+            @ptrToInt(instance),
+            &instance.thread.parent_tid,
+            tls_ptr,
+            &instance.thread.child_tid.value,
+        ))) {
+            0 => return Impl{ .thread = &instance.thread },
             os.EAGAIN => return error.ThreadQuotaExceeded,
             os.EINVAL => unreachable,
             os.ENOMEM => return error.SystemResources,
@@ -486,100 +712,92 @@ pub fn spawn(comptime startFn: anytype, context: SpawnContextType(@TypeOf(startF
             os.EUSERS => unreachable,
             else => |err| return os.unexpectedErrno(err),
         }
-    } else {
-        @compileError("Unsupported OS");
     }
-}
 
-pub const CpuCountError = error{
-    PermissionDenied,
-    SystemResources,
-    Unexpected,
-};
+    fn getHandle(self: Impl) ThreadHandle {
+        return self.thread.parent_tid;
+    }
 
-pub fn cpuCount() CpuCountError!usize {
-    switch (std.Target.current.os.tag) {
-        .linux => {
-            const cpu_set = try os.sched_getaffinity(0);
-            return @as(usize, os.CPU_COUNT(cpu_set)); // TODO should not need this usize cast
-        },
-        .windows => {
-            return os.windows.peb().NumberOfProcessors;
-        },
-        .openbsd => {
-            var count: c_int = undefined;
-            var count_size: usize = @sizeOf(c_int);
-            const mib = [_]c_int{ os.CTL_HW, os.HW_NCPUONLINE };
-            os.sysctl(&mib, &count, &count_size, null, 0) catch |err| switch (err) {
-                error.NameTooLong, error.UnknownName => unreachable,
-                else => |e| return e,
-            };
-            return @intCast(usize, count);
-        },
-        .haiku => {
-            var count: u32 = undefined;
-            // var system_info: os.system_info = undefined;
-            // const rc = os.system.get_system_info(&system_info);
-            count = system_info.cpu_count;
-            return @intCast(usize, count);
-        },
-        else => {
-            var count: c_int = undefined;
-            var count_len: usize = @sizeOf(c_int);
-            const name = if (comptime std.Target.current.isDarwin()) "hw.logicalcpu" else "hw.ncpu";
-            os.sysctlbynameZ(name, &count, &count_len, null, 0) catch |err| switch (err) {
-                error.NameTooLong, error.UnknownName => unreachable,
-                else => |e| return e,
-            };
-            return @intCast(usize, count);
-        },
+    fn detach(self: Impl) void {
+        switch (self.thread.completion.swap(.detached, .SeqCst)) {
+            .running => {},
+            .completed => self.join(),
+            .detached => unreachable,
+        }
     }
-}
 
-pub fn getCurrentThreadId() u64 {
-    switch (std.Target.current.os.tag) {
-        .linux => {
-            // Use the syscall directly as musl doesn't provide a wrapper.
-            return @bitCast(u32, os.linux.gettid());
-        },
-        .windows => {
-            return os.windows.kernel32.GetCurrentThreadId();
-        },
-        .macos, .ios, .watchos, .tvos => {
-            var thread_id: u64 = undefined;
-            // Pass thread=null to get the current thread ID.
-            assert(c.pthread_threadid_np(null, &thread_id) == 0);
-            return thread_id;
-        },
-        .dragonfly => {
-            return @bitCast(u32, c.lwp_gettid());
-        },
-        .netbsd => {
-            return @bitCast(u32, c._lwp_self());
-        },
-        .freebsd => {
-            return @bitCast(u32, c.pthread_getthreadid_np());
-        },
-        .openbsd => {
-            return @bitCast(u32, c.getthrid());
-        },
-        .haiku => {
-            return @bitCast(u32, c.find_thread(null));
-        },
-        else => {
-            @compileError("getCurrentThreadId not implemented for this platform");
-        },
+    fn join(self: Impl) void {
+        defer os.munmap(self.thread.mapped);
+
+        var spin: u8 = 10;
+        while (true) {
+            const tid = self.thread.child_tid.load(.SeqCst);
+            if (tid == 0) {
+                break;
+            }
+
+            if (spin > 0) {
+                spin -= 1;
+                std.atomic.spinLoopHint();
+                continue;
+            }
+
+            switch (linux.getErrno(linux.futex_wait(
+                &self.thread.child_tid.value,
+                linux.FUTEX_WAIT,
+                tid,
+                null,
+            ))) {
+                0 => continue,
+                os.EINTR => continue,
+                os.EAGAIN => continue,
+                else => unreachable,
+            }
+        }
     }
-}
+};
 
 test "std.Thread" {
-    if (!builtin.single_threaded) {
-        _ = AutoResetEvent;
-        _ = Futex;
-        _ = ResetEvent;
-        _ = StaticResetEvent;
-        _ = Mutex;
-        _ = Semaphore;
-        _ = Condition;
-    }
+    // Doesn't use testing.refAllDecls() since that would pull in the compileError spinLoopHint.
+    _ = AutoResetEvent;
+    _ = Futex;
+    _ = ResetEvent;
+    _ = StaticResetEvent;
+    _ = Mutex;
+    _ = Semaphore;
+    _ = Condition;
+}
+
+fn testIncrementNotify(value: *usize, event: *ResetEvent) void {
+    value.* += 1;
+    event.set();
+}
+
+test "Thread.join" {
+    if (std.builtin.single_threaded) return error.SkipZigTest;
+
+    var value: usize = 0;
+    var event: ResetEvent = undefined;
+    try event.init();
+    defer event.deinit();
+
+    const thread = try Thread.spawn(.{}, testIncrementNotify, .{ &value, &event });
+    thread.join();
+
+    try std.testing.expectEqual(value, 1);
+}
+
+test "Thread.detach" {
+    if (std.builtin.single_threaded) return error.SkipZigTest;
+
+    var value: usize = 0;
+    var event: ResetEvent = undefined;
+    try event.init();
+    defer event.deinit();
+
+    const thread = try Thread.spawn(.{}, testIncrementNotify, .{ &value, &event });
+    thread.detach();
+
+    event.wait();
+    try std.testing.expectEqual(value, 1);
 }
diff --git a/lib/std/Thread/AutoResetEvent.zig b/lib/std/Thread/AutoResetEvent.zig
index 7372a8d8d9..13e404d602 100644
--- a/lib/std/Thread/AutoResetEvent.zig
+++ b/lib/std/Thread/AutoResetEvent.zig
@@ -220,9 +220,9 @@ test "basic usage" {
     };
 
     var context = Context{};
-    const send_thread = try std.Thread.spawn(Context.sender, &context);
-    const recv_thread = try std.Thread.spawn(Context.receiver, &context);
+    const send_thread = try std.Thread.spawn(.{}, Context.sender, .{&context});
+    const recv_thread = try std.Thread.spawn(.{}, Context.receiver, .{&context});
 
-    send_thread.wait();
-    recv_thread.wait();
+    send_thread.join();
+    recv_thread.join();
 }
diff --git a/lib/std/Thread/Futex.zig b/lib/std/Thread/Futex.zig
index 356a4e2046..2a18711231 100644
--- a/lib/std/Thread/Futex.zig
+++ b/lib/std/Thread/Futex.zig
@@ -64,9 +64,8 @@ pub fn wait(ptr: *const Atomic(u32), expect: u32, timeout: ?u64) error{TimedOut}
 /// Unblocks at most `num_waiters` callers blocked in a `wait()` call on `ptr`.
 /// `num_waiters` of 1 unblocks at most one `wait(ptr, ...)` and `maxInt(u32)` unblocks effectively all `wait(ptr, ...)`.
 pub fn wake(ptr: *const Atomic(u32), num_waiters: u32) void {
-    if (num_waiters == 0 or single_threaded) {
-        return;
-    }
+    if (single_threaded) return;
+    if (num_waiters == 0) return;
 
     return OsFutex.wake(ptr, num_waiters);
 }
@@ -80,7 +79,23 @@ else if (target.isDarwin())
 else if (std.builtin.link_libc)
     PosixFutex
 else
-    @compileError("Operating System unsupported");
+    UnsupportedFutex;
+
+const UnsupportedFutex = struct {
+    fn wait(ptr: *const Atomic(u32), expect: u32, timeout: ?u64) error{TimedOut}!void {
+        return unsupported(.{ ptr, expect, timeout });
+    }
+
+    fn wake(ptr: *const Atomic(u32), num_waiters: u32) void {
+        return unsupported(.{ ptr, num_waiters });
+    }
+
+    fn unsupported(unused: anytype) noreturn {
+        @compileLog("Unsupported operating system", target.os.tag);
+        _ = unused;
+        unreachable;
+    }
+};
 
 const WindowsFutex = struct {
     const windows = std.os.windows;
@@ -391,75 +406,73 @@ test "Futex - wait/wake" {
 }
 
 test "Futex - Signal" {
-    if (!single_threaded) {
-        return;
+    if (single_threaded) {
+        return error.SkipZigTest;
     }
 
-    try (struct {
+    const Paddle = struct {
         value: Atomic(u32) = Atomic(u32).init(0),
+        current: u32 = 0,
 
-        const Self = @This();
+        fn run(self: *@This(), hit_to: *@This()) !void {
+            var iterations: usize = 4;
+            while (iterations > 0) : (iterations -= 1) {
+                var value: u32 = undefined;
+                while (true) {
+                    value = self.value.load(.Acquire);
+                    if (value != self.current) break;
+                    Futex.wait(&self.value, self.current, null) catch unreachable;
+                }
 
-        fn send(self: *Self, value: u32) void {
-            self.value.store(value, .Release);
-            Futex.wake(&self.value, 1);
-        }
+                try testing.expectEqual(value, self.current + 1);
+                self.current = value;
 
-        fn recv(self: *Self, expected: u32) void {
-            while (true) {
-                const value = self.value.load(.Acquire);
-                if (value == expected) break;
-                Futex.wait(&self.value, value, null) catch unreachable;
+                _ = hit_to.value.fetchAdd(1, .Release);
+                Futex.wake(&hit_to.value, 1);
             }
         }
+    };
 
-        const Thread = struct {
-            tx: *Self,
-            rx: *Self,
-
-            const start_value = 1;
-
-            fn run(self: Thread) void {
-                var iterations: u32 = start_value;
-                while (iterations < 10) : (iterations += 1) {
-                    self.rx.recv(iterations);
-                    self.tx.send(iterations);
-                }
-            }
-        };
-
-        fn run() !void {
-            var ping = Self{};
-            var pong = Self{};
+    var ping = Paddle{};
+    var pong = Paddle{};
 
-            const t1 = try std.Thread.spawn(Thread.run, .{ .rx = &ping, .tx = &pong });
-            defer t1.wait();
+    const t1 = try std.Thread.spawn(.{}, Paddle.run, .{ &ping, &pong });
+    defer t1.join();
 
-            const t2 = try std.Thread.spawn(Thread.run, .{ .rx = &pong, .tx = &ping });
-            defer t2.wait();
+    const t2 = try std.Thread.spawn(.{}, Paddle.run, .{ &pong, &ping });
+    defer t2.join();
 
-            ping.send(Thread.start_value);
-        }
-    }).run();
+    _ = ping.value.fetchAdd(1, .Release);
+    Futex.wake(&ping.value, 1);
 }
 
 test "Futex - Broadcast" {
-    if (!single_threaded) {
-        return;
+    if (single_threaded) {
+        return error.SkipZigTest;
     }
 
-    try (struct {
-        threads: [10]*std.Thread = undefined,
+    const Context = struct {
+        threads: [4]std.Thread = undefined,
         broadcast: Atomic(u32) = Atomic(u32).init(0),
         notified: Atomic(usize) = Atomic(usize).init(0),
 
-        const Self = @This();
-
         const BROADCAST_EMPTY = 0;
         const BROADCAST_SENT = 1;
         const BROADCAST_RECEIVED = 2;
 
-        fn runReceiver(self: *Self) void {
+        fn runSender(self: *@This()) !void {
+            self.broadcast.store(BROADCAST_SENT, .Monotonic);
+            Futex.wake(&self.broadcast, @intCast(u32, self.threads.len));
+
+            while (true) {
+                const broadcast = self.broadcast.load(.Acquire);
+                if (broadcast == BROADCAST_RECEIVED) break;
+                try testing.expectEqual(broadcast, BROADCAST_SENT);
+                Futex.wait(&self.broadcast, broadcast, null) catch unreachable;
+            }
+        }
+
+        fn runReceiver(self: *@This()) void {
             while (true) {
                 const broadcast = self.broadcast.load(.Acquire);
                 if (broadcast == BROADCAST_SENT) break;
@@ -473,98 +486,77 @@ test "Futex - Broadcast" {
                 Futex.wake(&self.broadcast, 1);
             }
         }
+    };
 
-        fn run() !void {
-            var self = Self{};
-
-            for (self.threads) |*thread|
-                thread.* = try std.Thread.spawn(runReceiver, &self);
-            defer for (self.threads) |thread|
-                thread.wait();
+    var ctx = Context{};
+    for (ctx.threads) |*thread|
+        thread.* = try std.Thread.spawn(.{}, Context.runReceiver, .{&ctx});
+    defer for (ctx.threads) |thread|
+        thread.join();
 
-            std.time.sleep(16 * std.time.ns_per_ms);
-            self.broadcast.store(BROADCAST_SENT, .Monotonic);
-            Futex.wake(&self.broadcast, @intCast(u32, self.threads.len));
+    // Try to wait for the threads to start before running runSender().
+    // NOTE: not actually needed for correctness.
+    std.time.sleep(16 * std.time.ns_per_ms);
+    try ctx.runSender();
 
-            while (true) {
-                const broadcast = self.broadcast.load(.Acquire);
-                if (broadcast == BROADCAST_RECEIVED) break;
-                try testing.expectEqual(broadcast, BROADCAST_SENT);
-                Futex.wait(&self.broadcast, broadcast, null) catch unreachable;
-            }
-
-            const notified = self.notified.load(.Monotonic);
-            try testing.expectEqual(notified, self.threads.len);
-        }
-    }).run();
+    const notified = ctx.notified.load(.Monotonic);
+    try testing.expectEqual(notified, ctx.threads.len);
 }
 
 test "Futex - Chain" {
-    if (!single_threaded) {
-        return;
+    if (single_threaded) {
+        return error.SkipZigTest;
     }
 
-    try (struct {
-        completed: Signal = .{},
-        threads: [10]struct {
-            thread: *std.Thread,
-            signal: Signal,
-        } = undefined,
-
-        const Signal = struct {
-            state: Atomic(u32) = Atomic(u32).init(0),
-
-            fn wait(self: *Signal) void {
-                while (true) {
-                    const value = self.value.load(.Acquire);
-                    if (value == 1) break;
-                    assert(value == 0);
-                    Futex.wait(&self.value, 0, null) catch unreachable;
-                }
-            }
+    const Signal = struct {
+        value: Atomic(u32) = Atomic(u32).init(0),
 
-            fn notify(self: *Signal) void {
-                assert(self.value.load(.Unordered) == 0);
-                self.value.store(1, .Release);
-                Futex.wake(&self.value, 1);
+        fn wait(self: *@This()) void {
+            while (true) {
+                const value = self.value.load(.Acquire);
+                if (value == 1) break;
+                assert(value == 0);
+                Futex.wait(&self.value, 0, null) catch unreachable;
             }
-        };
+        }
 
-        const Self = @This();
-        const Chain = struct {
-            self: *Self,
-            index: usize,
+        fn notify(self: *@This()) void {
+            assert(self.value.load(.Unordered) == 0);
+            self.value.store(1, .Release);
+            Futex.wake(&self.value, 1);
+        }
+    };
 
-            fn run(chain: Chain) void {
-                const this_signal = &chain.self.threads[chain.index].signal;
+    const Context = struct {
+        completed: Signal = .{},
+        threads: [4]struct {
+            thread: std.Thread,
+            signal: Signal,
+        } = undefined,
 
-                var next_signal = &chain.self.completed;
-                if (chain.index + 1 < chain.self.threads.len) {
-                    next_signal = &chain.self.threads[chain.index + 1].signal;
-                }
+        fn run(self: *@This(), index: usize) void {
+            const this_signal = &self.threads[index].signal;
 
-                this_signal.wait();
-                next_signal.notify();
+            var next_signal = &self.completed;
+            if (index + 1 < self.threads.len) {
+                next_signal = &self.threads[index + 1].signal;
             }
-        };
 
-        fn run() !void {
-            var self = Self{};
+            this_signal.wait();
+            next_signal.notify();
+        }
+    };
 
-            for (self.threads) |*entry, index| {
-                entry.signal = .{};
-                entry.thread = try std.Thread.spawn(Chain.run, .{
-                    .self = &self,
-                    .index = index,
-                });
-            }
+    var ctx = Context{};
+    for (ctx.threads) |*entry, index| {
+        entry.signal = .{};
+        entry.thread = try std.Thread.spawn(.{}, Context.run, .{ &ctx, index });
+    }
 
-            self.threads[0].signal.notify();
-            self.completed.wait();
+    ctx.threads[0].signal.notify();
+    ctx.completed.wait();
 
-            for (self.threads) |entry| {
-                entry.thread.wait();
-            }
-        }
-    }).run();
+    for (ctx.threads) |entry| {
+        entry.thread.join();
+    }
 }
diff --git a/lib/std/Thread/Mutex.zig b/lib/std/Thread/Mutex.zig
index 49f138079d..35095b2a3c 100644
--- a/lib/std/Thread/Mutex.zig
+++ b/lib/std/Thread/Mutex.zig
@@ -297,12 +297,12 @@ test "basic usage" {
         try testing.expect(context.data == TestContext.incr_count);
     } else {
         const thread_count = 10;
-        var threads: [thread_count]*std.Thread = undefined;
+        var threads: [thread_count]std.Thread = undefined;
         for (threads) |*t| {
-            t.* = try std.Thread.spawn(worker, &context);
+            t.* = try std.Thread.spawn(.{}, worker, .{&context});
         }
         for (threads) |t|
-            t.wait();
+            t.join();
 
         try testing.expect(context.data == thread_count * TestContext.incr_count);
     }
diff --git a/lib/std/Thread/ResetEvent.zig b/lib/std/Thread/ResetEvent.zig
index f161b46aa0..356b8eb78d 100644
--- a/lib/std/Thread/ResetEvent.zig
+++ b/lib/std/Thread/ResetEvent.zig
@@ -281,8 +281,8 @@ test "basic usage" {
     var context: Context = undefined;
     try context.init();
     defer context.deinit();
-    const receiver = try std.Thread.spawn(Context.receiver, &context);
-    defer receiver.wait();
+    const receiver = try std.Thread.spawn(.{}, Context.receiver, .{&context});
+    defer receiver.join();
     try context.sender();
 
     if (false) {
@@ -290,8 +290,8 @@ test "basic usage" {
         // https://github.com/ziglang/zig/issues/7009
         var timed = Context.init();
         defer timed.deinit();
-        const sleeper = try std.Thread.spawn(Context.sleeper, &timed);
-        defer sleeper.wait();
+        const sleeper = try std.Thread.spawn(.{}, Context.sleeper, .{&timed});
+        defer sleeper.join();
         try timed.timedWaiter();
     }
 }
diff --git a/lib/std/Thread/StaticResetEvent.zig b/lib/std/Thread/StaticResetEvent.zig
index 6f869e0d89..40974938d0 100644
--- a/lib/std/Thread/StaticResetEvent.zig
+++ b/lib/std/Thread/StaticResetEvent.zig
@@ -384,8 +384,8 @@ test "basic usage" {
     };
 
     var context = Context{};
-    const receiver = try std.Thread.spawn(Context.receiver, &context);
-    defer receiver.wait();
+    const receiver = try std.Thread.spawn(.{}, Context.receiver, .{&context});
+    defer receiver.join();
     try context.sender();
 
     if (false) {
@@ -393,8 +393,8 @@ test "basic usage" {
         // https://github.com/ziglang/zig/issues/7009
         var timed = Context.init();
         defer timed.deinit();
-        const sleeper = try std.Thread.spawn(Context.sleeper, &timed);
-        defer sleeper.wait();
+        const sleeper = try std.Thread.spawn(.{}, Context.sleeper, .{&timed});
+        defer sleeper.join();
         try timed.timedWaiter();
     }
 }
diff --git a/lib/std/atomic/queue.zig b/lib/std/atomic/queue.zig
index cc5b20488b..cee431951c 100644
--- a/lib/std/atomic/queue.zig
+++ b/lib/std/atomic/queue.zig
@@ -214,20 +214,20 @@ test "std.atomic.Queue" {
     } else {
         try expect(context.queue.isEmpty());
 
-        var putters: [put_thread_count]*std.Thread = undefined;
+        var putters: [put_thread_count]std.Thread = undefined;
         for (putters) |*t| {
-            t.* = try std.Thread.spawn(startPuts, &context);
+            t.* = try std.Thread.spawn(.{}, startPuts, .{&context});
         }
-        var getters: [put_thread_count]*std.Thread = undefined;
+        var getters: [put_thread_count]std.Thread = undefined;
         for (getters) |*t| {
-            t.* = try std.Thread.spawn(startGets, &context);
+            t.* = try std.Thread.spawn(.{}, startGets, .{&context});
         }
 
         for (putters) |t|
-            t.wait();
+            t.join();
         @atomicStore(bool, &context.puts_done, true, .SeqCst);
         for (getters) |t|
-            t.wait();
+            t.join();
 
         try expect(context.queue.isEmpty());
     }
diff --git a/lib/std/atomic/stack.zig b/lib/std/atomic/stack.zig
index 9472df7347..cfdf40fa60 100644
--- a/lib/std/atomic/stack.zig
+++ b/lib/std/atomic/stack.zig
@@ -121,20 +121,20 @@ test "std.atomic.stack" {
             }
         }
     } else {
-        var putters: [put_thread_count]*std.Thread = undefined;
+        var putters: [put_thread_count]std.Thread = undefined;
         for (putters) |*t| {
-            t.* = try std.Thread.spawn(startPuts, &context);
+            t.* = try std.Thread.spawn(.{}, startPuts, .{&context});
         }
-        var getters: [put_thread_count]*std.Thread = undefined;
+        var getters: [put_thread_count]std.Thread = undefined;
         for (getters) |*t| {
-            t.* = try std.Thread.spawn(startGets, &context);
+            t.* = try std.Thread.spawn(.{}, startGets, .{&context});
         }
 
         for (putters) |t|
-            t.wait();
+            t.join();
         @atomicStore(bool, &context.puts_done, true, .SeqCst);
         for (getters) |t|
-            t.wait();
+            t.join();
     }
 
     if (context.put_sum != context.get_sum) {
diff --git a/lib/std/c.zig b/lib/std/c.zig
index 2a8915bd1b..a3fe814a71 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -277,6 +277,7 @@ pub extern "c" fn pthread_attr_setguardsize(attr: *pthread_attr_t, guardsize: us
 pub extern "c" fn pthread_attr_destroy(attr: *pthread_attr_t) c_int;
 pub extern "c" fn pthread_self() pthread_t;
 pub extern "c" fn pthread_join(thread: pthread_t, arg_return: ?*?*c_void) c_int;
+pub extern "c" fn pthread_detach(thread: pthread_t) c_int;
 pub extern "c" fn pthread_atfork(
     prepare: ?fn () callconv(.C) void,
     parent: ?fn () callconv(.C) void,
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index fa87e5898c..57445d3cb1 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -273,8 +273,8 @@ pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, c
                 if (builtin.single_threaded) {
                     stderr.print("panic: ", .{}) catch os.abort();
                 } else {
-                    const current_thread_id = std.Thread.getCurrentThreadId();
-                    stderr.print("thread {d} panic: ", .{current_thread_id}) catch os.abort();
+                    const current_thread_id = std.Thread.getCurrentId();
+                    stderr.print("thread {} panic: ", .{current_thread_id}) catch os.abort();
                 }
                 stderr.print(format ++ "\n", args) catch os.abort();
                 if (trace) |t| {
diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index 5353341363..9c8550d459 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -21,12 +21,12 @@ pub const Loop = struct {
     os_data: OsData,
     final_resume_node: ResumeNode,
     pending_event_count: usize,
-    extra_threads: []*Thread,
+    extra_threads: []Thread,
     /// TODO change this to a pool of configurable number of threads
     /// and rename it to be not file-system-specific. it will become
     /// a thread pool for turning non-CPU-bound blocking things into
     /// async things. A fallback for any missing OS-specific API.
-    fs_thread: *Thread,
+    fs_thread: Thread,
     fs_queue: std.atomic.Queue(Request),
     fs_end_request: Request.Node,
     fs_thread_wakeup: std.Thread.ResetEvent,
@@ -137,7 +137,7 @@ pub const Loop = struct {
     }
 
     /// After initialization, call run().
-    /// This is the same as `initThreadPool` using `Thread.cpuCount` to determine the thread
+    /// This is the same as `initThreadPool` using `Thread.getCpuCount` to determine the thread
     /// pool size.
     /// TODO copy elision / named return values so that the threads referencing *Loop
     /// have the correct pointer value.
@@ -145,7 +145,7 @@ pub const Loop = struct {
     pub fn initMultiThreaded(self: *Loop) !void {
         if (builtin.single_threaded)
             @compileError("initMultiThreaded unavailable when building in single-threaded mode");
-        const core_count = try Thread.cpuCount();
+        const core_count = try Thread.getCpuCount();
         return self.initThreadPool(core_count);
     }
 
@@ -183,17 +183,17 @@ pub const Loop = struct {
             resume_node_count,
         );
 
-        self.extra_threads = try self.arena.allocator.alloc(*Thread, extra_thread_count);
+        self.extra_threads = try self.arena.allocator.alloc(Thread, extra_thread_count);
 
         try self.initOsData(extra_thread_count);
         errdefer self.deinitOsData();
 
         if (!builtin.single_threaded) {
-            self.fs_thread = try Thread.spawn(posixFsRun, self);
+            self.fs_thread = try Thread.spawn(.{}, posixFsRun, .{self});
         }
         errdefer if (!builtin.single_threaded) {
             self.posixFsRequest(&self.fs_end_request);
-            self.fs_thread.wait();
+            self.fs_thread.join();
         };
 
         if (!std.builtin.single_threaded)
@@ -264,11 +264,11 @@ pub const Loop = struct {
                     assert(amt == wakeup_bytes.len);
                     while (extra_thread_index != 0) {
                         extra_thread_index -= 1;
-                        self.extra_threads[extra_thread_index].wait();
+                        self.extra_threads[extra_thread_index].join();
                     }
                 }
                 while (extra_thread_index < extra_thread_count) : (extra_thread_index += 1) {
-                    self.extra_threads[extra_thread_index] = try Thread.spawn(workerRun, self);
+                    self.extra_threads[extra_thread_index] = try Thread.spawn(.{}, workerRun, .{self});
                 }
             },
             .macos, .freebsd, .netbsd, .dragonfly, .openbsd => {
@@ -329,11 +329,11 @@ pub const Loop = struct {
                     _ = os.kevent(self.os_data.kqfd, final_kev_arr, empty_kevs, null) catch unreachable;
                     while (extra_thread_index != 0) {
                         extra_thread_index -= 1;
-                        self.extra_threads[extra_thread_index].wait();
+                        self.extra_threads[extra_thread_index].join();
                     }
                 }
                 while (extra_thread_index < extra_thread_count) : (extra_thread_index += 1) {
-                    self.extra_threads[extra_thread_index] = try Thread.spawn(workerRun, self);
+                    self.extra_threads[extra_thread_index] = try Thread.spawn(.{}, workerRun, .{self});
                 }
             },
             .windows => {
@@ -378,11 +378,11 @@ pub const Loop = struct {
                     }
                     while (extra_thread_index != 0) {
                         extra_thread_index -= 1;
-                        self.extra_threads[extra_thread_index].wait();
+                        self.extra_threads[extra_thread_index].join();
                     }
                 }
                 while (extra_thread_index < extra_thread_count) : (extra_thread_index += 1) {
-                    self.extra_threads[extra_thread_index] = try Thread.spawn(workerRun, self);
+                    self.extra_threads[extra_thread_index] = try Thread.spawn(.{}, workerRun, .{self});
                 }
             },
             else => {},
@@ -651,18 +651,18 @@ pub const Loop = struct {
                 .netbsd,
                 .dragonfly,
                 .openbsd,
-                => self.fs_thread.wait(),
+                => self.fs_thread.join(),
                 else => {},
             }
         }
 
         for (self.extra_threads) |extra_thread| {
-            extra_thread.wait();
+            extra_thread.join();
         }
 
         @atomicStore(bool, &self.delay_queue.is_running, false, .SeqCst);
         self.delay_queue.event.set();
-        self.delay_queue.thread.wait();
+        self.delay_queue.thread.join();
     }
 
     /// Runs the provided function asynchronously. The function's frame is allocated
@@ -787,7 +787,7 @@ pub const Loop = struct {
     const DelayQueue = struct {
         timer: std.time.Timer,
         waiters: Waiters,
-        thread: *std.Thread,
+        thread: std.Thread,
         event: std.Thread.AutoResetEvent,
         is_running: bool,
 
@@ -802,7 +802,7 @@ pub const Loop = struct {
                 .event = std.Thread.AutoResetEvent{},
                 .is_running = true,
                 // Must be last so that it can read the other state, such as `is_running`.
-                .thread = try std.Thread.spawn(DelayQueue.run, self),
+                .thread = try std.Thread.spawn(.{}, DelayQueue.run, .{self}),
             };
         }
 
diff --git a/lib/std/fs/test.zig b/lib/std/fs/test.zig
index 3c7a95432c..9464959cdb 100644
--- a/lib/std/fs/test.zig
+++ b/lib/std/fs/test.zig
@@ -862,11 +862,10 @@ test "open file with exclusive lock twice, make sure it waits" {
     errdefer file.close();
 
     const S = struct {
-        const C = struct { dir: *fs.Dir, evt: *std.Thread.ResetEvent };
-        fn checkFn(ctx: C) !void {
-            const file1 = try ctx.dir.createFile(filename, .{ .lock = .Exclusive });
+        fn checkFn(dir: *fs.Dir, evt: *std.Thread.ResetEvent) !void {
+            const file1 = try dir.createFile(filename, .{ .lock = .Exclusive });
             defer file1.close();
-            ctx.evt.set();
+            evt.set();
         }
     };
 
@@ -874,8 +873,8 @@ test "open file with exclusive lock twice, make sure it waits" {
     try evt.init();
     defer evt.deinit();
 
-    const t = try std.Thread.spawn(S.checkFn, S.C{ .dir = &tmp.dir, .evt = &evt });
-    defer t.wait();
+    const t = try std.Thread.spawn(.{}, S.checkFn, .{ &tmp.dir, &evt });
+    defer t.join();
 
     const SLEEP_TIMEOUT_NS = 10 * std.time.ns_per_ms;
     // Make sure we've slept enough.
diff --git a/lib/std/net/test.zig b/lib/std/net/test.zig
index c2596b733c..08722c9e31 100644
--- a/lib/std/net/test.zig
+++ b/lib/std/net/test.zig
@@ -161,8 +161,8 @@ test "listen on a port, send bytes, receive bytes" {
         }
     };
 
-    const t = try std.Thread.spawn(S.clientFn, server.listen_address);
-    defer t.wait();
+    const t = try std.Thread.spawn(.{}, S.clientFn, .{server.listen_address});
+    defer t.join();
 
     var client = try server.accept();
     defer client.stream.close();
@@ -277,7 +277,7 @@ test "listen on a unix socket, send bytes, receive bytes" {
     try server.listen(socket_addr);
 
     const S = struct {
-        fn clientFn(_: void) !void {
+        fn clientFn() !void {
             const socket = try net.connectUnixSocket(socket_path);
             defer socket.close();
 
@@ -285,8 +285,8 @@ test "listen on a unix socket, send bytes, receive bytes" {
         }
     };
 
-    const t = try std.Thread.spawn(S.clientFn, {});
-    defer t.wait();
+    const t = try std.Thread.spawn(.{}, S.clientFn, .{});
+    defer t.join();
 
     var client = try server.accept();
     defer client.stream.close();
diff --git a/lib/std/once.zig b/lib/std/once.zig
index 05f003c796..a557f4aac9 100644
--- a/lib/std/once.zig
+++ b/lib/std/once.zig
@@ -55,16 +55,16 @@ test "Once executes its function just once" {
         global_once.call();
         global_once.call();
     } else {
-        var threads: [10]*std.Thread = undefined;
-        defer for (threads) |handle| handle.wait();
+        var threads: [10]std.Thread = undefined;
+        defer for (threads) |handle| handle.join();
 
         for (threads) |*handle| {
-            handle.* = try std.Thread.spawn(struct {
+            handle.* = try std.Thread.spawn(.{}, struct {
                 fn thread_fn(x: u8) void {
                     _ = x;
                     global_once.call();
                 }
-            }.thread_fn, 0);
+            }.thread_fn, .{0});
         }
     }
 
diff --git a/lib/std/os/test.zig b/lib/std/os/test.zig
index 7a88ecd7ca..6184c97706 100644
--- a/lib/std/os/test.zig
+++ b/lib/std/os/test.zig
@@ -320,18 +320,9 @@ test "std.Thread.getCurrentId" {
     if (builtin.single_threaded) return error.SkipZigTest;
 
     var thread_current_id: Thread.Id = undefined;
-    const thread = try Thread.spawn(testThreadIdFn, &thread_current_id);
-    const thread_id = thread.handle();
-    thread.wait();
-    if (Thread.use_pthreads) {
-        try expect(thread_current_id == thread_id);
-    } else if (native_os == .windows) {
-        try expect(Thread.getCurrentId() != thread_current_id);
-    } else {
-        // If the thread completes very quickly, then thread_id can be 0. See the
-        // documentation comments for `std.Thread.handle`.
-        try expect(thread_id == 0 or thread_current_id == thread_id);
-    }
+    const thread = try Thread.spawn(.{}, testThreadIdFn, .{&thread_current_id});
+    thread.join();
+    try expect(Thread.getCurrentId() != thread_current_id);
 }
 
 test "spawn threads" {
@@ -339,21 +330,20 @@ test "spawn threads" {
 
     var shared_ctx: i32 = 1;
 
-    const thread1 = try Thread.spawn(start1, {});
-    const thread2 = try Thread.spawn(start2, &shared_ctx);
-    const thread3 = try Thread.spawn(start2, &shared_ctx);
-    const thread4 = try Thread.spawn(start2, &shared_ctx);
+    const thread1 = try Thread.spawn(.{}, start1, .{});
+    const thread2 = try Thread.spawn(.{}, start2, .{&shared_ctx});
+    const thread3 = try Thread.spawn(.{}, start2, .{&shared_ctx});
+    const thread4 = try Thread.spawn(.{}, start2, .{&shared_ctx});
 
-    thread1.wait();
-    thread2.wait();
-    thread3.wait();
-    thread4.wait();
+    thread1.join();
+    thread2.join();
+    thread3.join();
+    thread4.join();
 
     try expect(shared_ctx == 4);
 }
 
-fn start1(ctx: void) u8 {
-    _ = ctx;
+fn start1() u8 {
     return 0;
 }
 
@@ -365,22 +355,21 @@ fn start2(ctx: *i32) u8 {
 test "cpu count" {
     if (native_os == .wasi) return error.SkipZigTest;
 
-    const cpu_count = try Thread.cpuCount();
+    const cpu_count = try Thread.getCpuCount();
     try expect(cpu_count >= 1);
 }
 
 test "thread local storage" {
     if (builtin.single_threaded) return error.SkipZigTest;
-    const thread1 = try Thread.spawn(testTls, {});
-    const thread2 = try Thread.spawn(testTls, {});
-    try testTls({});
-    thread1.wait();
-    thread2.wait();
+    const thread1 = try Thread.spawn(.{}, testTls, .{});
+    const thread2 = try Thread.spawn(.{}, testTls, .{});
+    try testTls();
+    thread1.join();
+    thread2.join();
 }
 
 threadlocal var x: i32 = 1234;
-fn testTls(context: void) !void {
-    _ = context;
+fn testTls() !void {
     if (x != 1234) return error.TlsBadStartValue;
     x += 1;
     if (x != 1235) return error.TlsBadEndValue;
diff --git a/lib/std/target.zig b/lib/std/target.zig
index 02ce44d477..507f30c2e0 100644
--- a/lib/std/target.zig
+++ b/lib/std/target.zig
@@ -69,6 +69,13 @@ pub const Target = struct {
                 };
             }
 
+            pub fn isBSD(tag: Tag) bool {
+                return tag.isDarwin() or switch (tag) {
+                    .kfreebsd, .freebsd, .openbsd, .netbsd, .dragonfly => true,
+                    else => false,
+                };
+            }
+
             pub fn dynamicLibSuffix(tag: Tag) [:0]const u8 {
                 if (tag.isDarwin()) {
                     return ".dylib";
@@ -787,6 +794,13 @@ pub const Target = struct {
                 };
             }
 
+            pub fn isAARCH64(arch: Arch) bool {
+                return switch (arch) {
+                    .aarch64, .aarch64_be, .aarch64_32 => true,
+                    else => false,
+                };
+            }
+
             pub fn isThumb(arch: Arch) bool {
                 return switch (arch) {
                     .thumb, .thumbeb => true,
@@ -1365,10 +1379,7 @@ pub const Target = struct {
     }
 
     pub fn isAndroid(self: Target) bool {
-        return switch (self.abi) {
-            .android => true,
-            else => false,
-        };
+        return self.abi == .android;
     }
 
     pub fn isWasm(self: Target) bool {
@@ -1379,6 +1390,10 @@ pub const Target = struct {
         return self.os.tag.isDarwin();
     }
 
+    pub fn isBSD(self: Target) bool {
+        return self.os.tag.isBSD();
+    }
+
     pub fn isGnuLibC_os_tag_abi(os_tag: Os.Tag, abi: Abi) bool {
         return os_tag == .linux and abi.isGnu();
     }