std.event.Loop: promote the fs thread to be available for all OS's

6 files changed, 137 insertions, 193 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 97aa2b6e97..df84a8bbcb 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -112,39 +112,43 @@ pub fn detectTTYConfig() TTY.Config {
 /// Tries to print the current stack trace to stderr, unbuffered, and ignores any error returned.
 /// TODO multithreaded awareness
 pub fn dumpCurrentStackTrace(start_addr: ?usize) void {
-    const stderr = getStderrStream();
-    if (builtin.strip_debug_info) {
-        noasync stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
-        return;
+    noasync {
+        const stderr = getStderrStream();
+        if (builtin.strip_debug_info) {
+            stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
+            return;
+        }
+        const debug_info = getSelfDebugInfo() catch |err| {
+            stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
+            return;
+        };
+        writeCurrentStackTrace(stderr, debug_info, detectTTYConfig(), start_addr) catch |err| {
+            stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
+            return;
+        };
     }
-    const debug_info = getSelfDebugInfo() catch |err| {
-        noasync stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
-        return;
-    };
-    writeCurrentStackTrace(stderr, debug_info, detectTTYConfig(), start_addr) catch |err| {
-        noasync stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
-        return;
-    };
 }
 
 /// Tries to print the stack trace starting from the supplied base pointer to stderr,
 /// unbuffered, and ignores any error returned.
 /// TODO multithreaded awareness
 pub fn dumpStackTraceFromBase(bp: usize, ip: usize) void {
-    const stderr = getStderrStream();
-    if (builtin.strip_debug_info) {
-        noasync stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
-        return;
-    }
-    const debug_info = getSelfDebugInfo() catch |err| {
-        noasync stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
-        return;
-    };
-    const tty_config = detectTTYConfig();
-    printSourceAtAddress(debug_info, stderr, ip, tty_config) catch return;
-    var it = StackIterator.init(null, bp);
-    while (it.next()) |return_address| {
-        printSourceAtAddress(debug_info, stderr, return_address - 1, tty_config) catch return;
+    noasync {
+        const stderr = getStderrStream();
+        if (builtin.strip_debug_info) {
+            stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
+            return;
+        }
+        const debug_info = getSelfDebugInfo() catch |err| {
+            stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
+            return;
+        };
+        const tty_config = detectTTYConfig();
+        printSourceAtAddress(debug_info, stderr, ip, tty_config) catch return;
+        var it = StackIterator.init(null, bp);
+        while (it.next()) |return_address| {
+            printSourceAtAddress(debug_info, stderr, return_address - 1, tty_config) catch return;
+        }
     }
 }
 
@@ -199,19 +203,21 @@ pub fn captureStackTrace(first_address: ?usize, stack_trace: *builtin.StackTrace
 /// Tries to print a stack trace to stderr, unbuffered, and ignores any error returned.
 /// TODO multithreaded awareness
 pub fn dumpStackTrace(stack_trace: builtin.StackTrace) void {
-    const stderr = getStderrStream();
-    if (builtin.strip_debug_info) {
-        noasync stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
-        return;
+    noasync {
+        const stderr = getStderrStream();
+        if (builtin.strip_debug_info) {
+            stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
+            return;
+        }
+        const debug_info = getSelfDebugInfo() catch |err| {
+            stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
+            return;
+        };
+        writeStackTrace(stack_trace, stderr, getDebugInfoAllocator(), debug_info, detectTTYConfig()) catch |err| {
+            stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
+            return;
+        };
     }
-    const debug_info = getSelfDebugInfo() catch |err| {
-        noasync stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
-        return;
-    };
-    writeStackTrace(stack_trace, stderr, getDebugInfoAllocator(), debug_info, detectTTYConfig()) catch |err| {
-        noasync stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
-        return;
-    };
 }
 
 /// This function invokes undefined behavior when `ok` is `false`.
@@ -255,7 +261,7 @@ pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, c
         resetSegfaultHandler();
     }
 
-    switch (panic_stage) {
+    noasync switch (panic_stage) {
         0 => {
             panic_stage = 1;
 
@@ -267,7 +273,7 @@ pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, c
                 defer held.release();
 
                 const stderr = getStderrStream();
-                noasync stderr.print(format ++ "\n", args) catch os.abort();
+                stderr.print(format ++ "\n", args) catch os.abort();
                 if (trace) |t| {
                     dumpStackTrace(t.*);
                 }
@@ -292,12 +298,12 @@ pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, c
             // we're still holding the mutex but that's fine as we're going to
             // call abort()
             const stderr = getStderrStream();
-            noasync stderr.print("Panicked during a panic. Aborting.\n", .{}) catch os.abort();
+            stderr.print("Panicked during a panic. Aborting.\n", .{}) catch os.abort();
         },
         else => {
             // Panicked while printing "Panicked during a panic."
         },
-    }
+    };
 
     os.abort();
 }
diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index f0ac85d4f0..6337911cb6 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -4,19 +4,27 @@ const root = @import("root");
 const assert = std.debug.assert;
 const testing = std.testing;
 const mem = std.mem;
-const AtomicRmwOp = builtin.AtomicRmwOp;
-const AtomicOrder = builtin.AtomicOrder;
 const os = std.os;
 const windows = os.windows;
 const maxInt = std.math.maxInt;
 const Thread = std.Thread;
 
+const is_windows = std.Target.current.os.tag == .windows;
+
 pub const Loop = struct {
     next_tick_queue: std.atomic.Queue(anyframe),
     os_data: OsData,
     final_resume_node: ResumeNode,
     pending_event_count: usize,
     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_queue: std.atomic.Queue(Request),
+    fs_end_request: Request.Node,
+    fs_thread_wakeup: std.ResetEvent,
 
     /// For resources that have the same lifetime as the `Loop`.
     /// This is only used by `Loop` for the thread pool and associated resources.
@@ -143,7 +151,12 @@ pub const Loop = struct {
                 .handle = undefined,
                 .overlapped = ResumeNode.overlapped_init,
             },
+            .fs_end_request = .{ .data = .{ .msg = .end, .finish = .NoAction } },
+            .fs_queue = std.atomic.Queue(Request).init(),
+            .fs_thread = undefined,
+            .fs_thread_wakeup = std.ResetEvent.init(),
         };
+        errdefer self.fs_thread_wakeup.deinit();
         errdefer self.arena.deinit();
 
         // We need at least one of these in case the fs thread wants to use onNextTick
@@ -158,10 +171,19 @@ pub const Loop = struct {
 
         try self.initOsData(extra_thread_count);
         errdefer self.deinitOsData();
+
+        if (!builtin.single_threaded) {
+            self.fs_thread = try Thread.spawn(self, posixFsRun);
+        }
+        errdefer if (!builtin.single_threaded) {
+            self.posixFsRequest(&self.fs_end_request);
+            self.fs_thread.wait();
+        };
     }
 
     pub fn deinit(self: *Loop) void {
         self.deinitOsData();
+        self.fs_thread_wakeup.deinit();
         self.arena.deinit();
         self.* = undefined;
     }
@@ -173,21 +195,10 @@ pub const Loop = struct {
     const wakeup_bytes = [_]u8{0x1} ** 8;
 
     fn initOsData(self: *Loop, extra_thread_count: usize) InitOsDataError!void {
-        switch (builtin.os.tag) {
+        noasync switch (builtin.os.tag) {
             .linux => {
-                self.os_data.fs_queue = std.atomic.Queue(Request).init();
-                self.os_data.fs_queue_item = 0;
-                // we need another thread for the file system because Linux does not have an async
-                // file system I/O API.
-                self.os_data.fs_end_request = Request.Node{
-                    .data = Request{
-                        .msg = .end,
-                        .finish = .NoAction,
-                    },
-                };
-
                 errdefer {
-                    while (self.available_eventfd_resume_nodes.pop()) |node| noasync os.close(node.data.eventfd);
+                    while (self.available_eventfd_resume_nodes.pop()) |node| os.close(node.data.eventfd);
                 }
                 for (self.eventfd_resume_nodes) |*eventfd_node| {
                     eventfd_node.* = std.atomic.Stack(ResumeNode.EventFd).Node{
@@ -206,10 +217,10 @@ pub const Loop = struct {
                 }
 
                 self.os_data.epollfd = try os.epoll_create1(os.EPOLL_CLOEXEC);
-                errdefer noasync os.close(self.os_data.epollfd);
+                errdefer os.close(self.os_data.epollfd);
 
                 self.os_data.final_eventfd = try os.eventfd(0, os.EFD_CLOEXEC | os.EFD_NONBLOCK);
-                errdefer noasync os.close(self.os_data.final_eventfd);
+                errdefer os.close(self.os_data.final_eventfd);
 
                 self.os_data.final_eventfd_event = os.epoll_event{
                     .events = os.EPOLLIN,
@@ -222,12 +233,6 @@ pub const Loop = struct {
                     &self.os_data.final_eventfd_event,
                 );
 
-                self.os_data.fs_thread = try Thread.spawn(self, posixFsRun);
-                errdefer {
-                    self.posixFsRequest(&self.os_data.fs_end_request);
-                    self.os_data.fs_thread.wait();
-                }
-
                 if (builtin.single_threaded) {
                     assert(extra_thread_count == 0);
                     return;
@@ -236,7 +241,7 @@ pub const Loop = struct {
                 var extra_thread_index: usize = 0;
                 errdefer {
                     // writing 8 bytes to an eventfd cannot fail
-                    const amt = noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    const amt = os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
                     assert(amt == wakeup_bytes.len);
                     while (extra_thread_index != 0) {
                         extra_thread_index -= 1;
@@ -249,22 +254,7 @@ pub const Loop = struct {
             },
             .macosx, .freebsd, .netbsd, .dragonfly => {
                 self.os_data.kqfd = try os.kqueue();
-                errdefer noasync os.close(self.os_data.kqfd);
-
-                self.os_data.fs_kqfd = try os.kqueue();
-                errdefer noasync os.close(self.os_data.fs_kqfd);
-
-                self.os_data.fs_queue = std.atomic.Queue(Request).init();
-                // we need another thread for the file system because Darwin does not have an async
-                // file system I/O API.
-                self.os_data.fs_end_request = Request.Node{
-                    .prev = undefined,
-                    .next = undefined,
-                    .data = Request{
-                        .msg = .end,
-                        .finish = .NoAction,
-                    },
-                };
+                errdefer os.close(self.os_data.kqfd);
 
                 const empty_kevs = &[0]os.Kevent{};
 
@@ -310,30 +300,6 @@ pub const Loop = struct {
                 self.os_data.final_kevent.flags = os.EV_ENABLE;
                 self.os_data.final_kevent.fflags = os.NOTE_TRIGGER;
 
-                self.os_data.fs_kevent_wake = os.Kevent{
-                    .ident = 0,
-                    .filter = os.EVFILT_USER,
-                    .flags = os.EV_ADD | os.EV_ENABLE,
-                    .fflags = os.NOTE_TRIGGER,
-                    .data = 0,
-                    .udata = undefined,
-                };
-
-                self.os_data.fs_kevent_wait = os.Kevent{
-                    .ident = 0,
-                    .filter = os.EVFILT_USER,
-                    .flags = os.EV_ADD | os.EV_CLEAR,
-                    .fflags = 0,
-                    .data = 0,
-                    .udata = undefined,
-                };
-
-                self.os_data.fs_thread = try Thread.spawn(self, posixFsRun);
-                errdefer {
-                    self.posixFsRequest(&self.os_data.fs_end_request);
-                    self.os_data.fs_thread.wait();
-                }
-
                 if (builtin.single_threaded) {
                     assert(extra_thread_count == 0);
                     return;
@@ -401,25 +367,24 @@ pub const Loop = struct {
                 }
             },
             else => {},
-        }
+        };
     }
 
     fn deinitOsData(self: *Loop) void {
-        switch (builtin.os.tag) {
+        noasync switch (builtin.os.tag) {
             .linux => {
-                noasync os.close(self.os_data.final_eventfd);
-                while (self.available_eventfd_resume_nodes.pop()) |node| noasync os.close(node.data.eventfd);
-                noasync os.close(self.os_data.epollfd);
+                os.close(self.os_data.final_eventfd);
+                while (self.available_eventfd_resume_nodes.pop()) |node| os.close(node.data.eventfd);
+                os.close(self.os_data.epollfd);
             },
             .macosx, .freebsd, .netbsd, .dragonfly => {
-                noasync os.close(self.os_data.kqfd);
-                noasync os.close(self.os_data.fs_kqfd);
+                os.close(self.os_data.kqfd);
             },
             .windows => {
                 windows.CloseHandle(self.os_data.io_port);
             },
             else => {},
-        }
+        };
     }
 
     /// resume_node must live longer than the anyframe that it holds a reference to.
@@ -635,7 +600,7 @@ pub const Loop = struct {
             .freebsd,
             .netbsd,
             .dragonfly,
-            => self.os_data.fs_thread.wait(),
+            => self.fs_thread.wait(),
             else => {},
         }
 
@@ -672,23 +637,25 @@ pub const Loop = struct {
 
     /// call finishOneEvent when done
     pub fn beginOneEvent(self: *Loop) void {
-        _ = @atomicRmw(usize, &self.pending_event_count, AtomicRmwOp.Add, 1, AtomicOrder.SeqCst);
+        _ = @atomicRmw(usize, &self.pending_event_count, .Add, 1, .SeqCst);
     }
 
     pub fn finishOneEvent(self: *Loop) void {
-        const prev = @atomicRmw(usize, &self.pending_event_count, AtomicRmwOp.Sub, 1, AtomicOrder.SeqCst);
-        if (prev == 1) {
+        noasync {
+            const prev = @atomicRmw(usize, &self.pending_event_count, .Sub, 1, .SeqCst);
+            if (prev != 1) return;
+
             // cause all the threads to stop
+            self.posixFsRequest(&self.fs_end_request);
+
             switch (builtin.os.tag) {
                 .linux => {
-                    self.posixFsRequest(&self.os_data.fs_end_request);
                     // writing 8 bytes to an eventfd cannot fail
-                    const amt = noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    const amt = os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
                     assert(amt == wakeup_bytes.len);
                     return;
                 },
                 .macosx, .freebsd, .netbsd, .dragonfly => {
-                    self.posixFsRequest(&self.os_data.fs_end_request);
                     const final_kevent = @as(*const [1]os.Kevent, &self.os_data.final_kevent);
                     const empty_kevs = &[0]os.Kevent{};
                     // cannot fail because we already added it and this just enables it
@@ -1041,73 +1008,55 @@ pub const Loop = struct {
 
     fn posixFsRequest(self: *Loop, request_node: *Request.Node) void {
         self.beginOneEvent(); // finished in posixFsRun after processing the msg
-        self.os_data.fs_queue.put(request_node);
-        switch (builtin.os.tag) {
-            .macosx, .freebsd, .netbsd, .dragonfly => {
-                const fs_kevs = @as(*const [1]os.Kevent, &self.os_data.fs_kevent_wake);
-                const empty_kevs = &[0]os.Kevent{};
-                _ = os.kevent(self.os_data.fs_kqfd, fs_kevs, empty_kevs, null) catch unreachable;
-            },
-            .linux => {
-                @atomicStore(i32, &self.os_data.fs_queue_item, 1, AtomicOrder.SeqCst);
-                const rc = os.linux.futex_wake(&self.os_data.fs_queue_item, os.linux.FUTEX_WAKE, 1);
-                switch (os.linux.getErrno(rc)) {
-                    0 => {},
-                    os.EINVAL => unreachable,
-                    else => unreachable,
-                }
-            },
-            else => @compileError("Unsupported OS"),
-        }
+        self.fs_queue.put(request_node);
+        self.fs_thread_wakeup.set();
     }
 
     fn posixFsCancel(self: *Loop, request_node: *Request.Node) void {
-        if (self.os_data.fs_queue.remove(request_node)) {
+        if (self.fs_queue.remove(request_node)) {
             self.finishOneEvent();
         }
     }
 
-    // TODO make this whole function noasync
-    // https://github.com/ziglang/zig/issues/3157
     fn posixFsRun(self: *Loop) void {
-        while (true) {
-            if (builtin.os.tag == .linux) {
-                @atomicStore(i32, &self.os_data.fs_queue_item, 0, .SeqCst);
-            }
-            while (self.os_data.fs_queue.get()) |node| {
+        noasync while (true) {
+            self.fs_thread_wakeup.reset();
+            while (self.fs_queue.get()) |node| {
                 switch (node.data.msg) {
                     .end => return,
                     .read => |*msg| {
-                        msg.result = noasync os.read(msg.fd, msg.buf);
+                        msg.result = os.read(msg.fd, msg.buf);
                     },
                     .readv => |*msg| {
-                        msg.result = noasync os.readv(msg.fd, msg.iov);
+                        msg.result = os.readv(msg.fd, msg.iov);
                     },
                     .write => |*msg| {
-                        msg.result = noasync os.write(msg.fd, msg.bytes);
+                        msg.result = os.write(msg.fd, msg.bytes);
                     },
                     .writev => |*msg| {
-                        msg.result = noasync os.writev(msg.fd, msg.iov);
+                        msg.result = os.writev(msg.fd, msg.iov);
                     },
                     .pwritev => |*msg| {
-                        msg.result = noasync os.pwritev(msg.fd, msg.iov, msg.offset);
+                        msg.result = os.pwritev(msg.fd, msg.iov, msg.offset);
                     },
                     .pread => |*msg| {
-                        msg.result = noasync os.pread(msg.fd, msg.buf, msg.offset);
+                        msg.result = os.pread(msg.fd, msg.buf, msg.offset);
                     },
                     .preadv => |*msg| {
-                        msg.result = noasync os.preadv(msg.fd, msg.iov, msg.offset);
+                        msg.result = os.preadv(msg.fd, msg.iov, msg.offset);
                     },
                     .open => |*msg| {
-                        msg.result = noasync os.openZ(msg.path, msg.flags, msg.mode);
+                        if (is_windows) unreachable; // TODO
+                        msg.result = os.openZ(msg.path, msg.flags, msg.mode);
                     },
                     .openat => |*msg| {
-                        msg.result = noasync os.openatZ(msg.fd, msg.path, msg.flags, msg.mode);
+                        if (is_windows) unreachable; // TODO
+                        msg.result = os.openatZ(msg.fd, msg.path, msg.flags, msg.mode);
                     },
                     .faccessat => |*msg| {
-                        msg.result = noasync os.faccessatZ(msg.dirfd, msg.path, msg.mode, msg.flags);
+                        msg.result = os.faccessatZ(msg.dirfd, msg.path, msg.mode, msg.flags);
                     },
-                    .close => |*msg| noasync os.close(msg.fd),
+                    .close => |*msg| os.close(msg.fd),
                 }
                 switch (node.data.finish) {
                     .TickNode => |*tick_node| self.onNextTick(tick_node),
@@ -1115,22 +1064,8 @@ pub const Loop = struct {
                 }
                 self.finishOneEvent();
             }
-            switch (builtin.os.tag) {
-                .linux => {
-                    const rc = os.linux.futex_wait(&self.os_data.fs_queue_item, os.linux.FUTEX_WAIT, 0, null);
-                    switch (os.linux.getErrno(rc)) {
-                        0, os.EINTR, os.EAGAIN => continue,
-                        else => unreachable,
-                    }
-                },
-                .macosx, .freebsd, .netbsd, .dragonfly => {
-                    const fs_kevs = @as(*const [1]os.Kevent, &self.os_data.fs_kevent_wait);
-                    var out_kevs: [1]os.Kevent = undefined;
-                    _ = os.kevent(self.os_data.fs_kqfd, fs_kevs, out_kevs[0..], null) catch unreachable;
-                },
-                else => @compileError("Unsupported OS"),
-            }
-        }
+            self.fs_thread_wakeup.wait();
+        };
     }
 
     const OsData = switch (builtin.os.tag) {
@@ -1146,22 +1081,12 @@ pub const Loop = struct {
     const KEventData = struct {
         kqfd: i32,
         final_kevent: os.Kevent,
-        fs_kevent_wake: os.Kevent,
-        fs_kevent_wait: os.Kevent,
-        fs_thread: *Thread,
-        fs_kqfd: i32,
-        fs_queue: std.atomic.Queue(Request),
-        fs_end_request: Request.Node,
     };
 
     const LinuxOsData = struct {
         epollfd: i32,
         final_eventfd: i32,
         final_eventfd_event: os.linux.epoll_event,
-        fs_thread: *Thread,
-        fs_queue_item: i32,
-        fs_queue: std.atomic.Queue(Request),
-        fs_end_request: Request.Node,
     };
 
     pub const Request = struct {
@@ -1302,11 +1227,11 @@ test "std.event.Loop - basic" {
     loop.run();
 }
 
-async fn testEventLoop() i32 {
+fn testEventLoop() i32 {
     return 1234;
 }
 
-async fn testEventLoop2(h: anyframe->i32, did_it: *bool) void {
+fn testEventLoop2(h: anyframe->i32, did_it: *bool) void {
     const value = await h;
     testing.expect(value == 1234);
     did_it.* = true;
diff --git a/lib/std/fs.zig b/lib/std/fs.zig
index 99b43a66e3..7dcfc9261c 100644
--- a/lib/std/fs.zig
+++ b/lib/std/fs.zig
@@ -734,7 +734,7 @@ pub const Dir = struct {
                 .dir = self.fd,
                 .access_mask = w.SYNCHRONIZE | w.GENERIC_WRITE | read_flag,
                 .share_access = switch (flags.lock) {
-                    .None => @as(?w.ULONG, null),
+                    .None => w.FILE_SHARE_WRITE | w.FILE_SHARE_READ | w.FILE_SHARE_DELETE,
                     .Shared => w.FILE_SHARE_READ | w.FILE_SHARE_DELETE,
                     .Exclusive => w.FILE_SHARE_DELETE,
                 },
diff --git a/lib/std/os.zig b/lib/std/os.zig
index 05d8b60a2d..39f5d36ddf 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -854,8 +854,11 @@ pub const OpenError = error{
 
 /// Open and possibly create a file. Keeps trying if it gets interrupted.
 /// See also `openC`.
-/// TODO support windows
 pub fn open(file_path: []const u8, flags: u32, perm: usize) OpenError!fd_t {
+    if (std.Target.current.os.tag == .windows) {
+        const file_path_w = try windows.sliceToPrefixedFileW(file_path);
+        return openW(&file_path_w, flags, perm);
+    }
     const file_path_c = try toPosixPath(file_path);
     return openZ(&file_path_c, flags, perm);
 }
@@ -864,8 +867,11 @@ pub const openC = @compileError("deprecated: renamed to openZ");
 
 /// Open and possibly create a file. Keeps trying if it gets interrupted.
 /// See also `open`.
-/// TODO support windows
 pub fn openZ(file_path: [*:0]const u8, flags: u32, perm: usize) OpenError!fd_t {
+    if (std.Target.current.os.tag == .windows) {
+        const file_path_w = try windows.cStrToPrefixedFileW(file_path);
+        return openW(&file_path_w, flags, perm);
+    }
     while (true) {
         const rc = system.open(file_path, flags, perm);
         switch (errno(rc)) {
@@ -895,6 +901,13 @@ pub fn openZ(file_path: [*:0]const u8, flags: u32, perm: usize) OpenError!fd_t {
     }
 }
 
+/// Windows-only. The path parameter is
+/// [WTF-16](https://simonsapin.github.io/wtf-8/#potentially-ill-formed-utf-16) encoded.
+/// Translates the POSIX open API call to a Windows API call.
+pub fn openW(file_path_w: []const u16, flags: u32, perm: usize) OpenError!fd_t {
+    @compileError("TODO implement openW for windows");
+}
+
 /// Open and possibly create a file. Keeps trying if it gets interrupted.
 /// `file_path` is relative to the open directory handle `dir_fd`.
 /// See also `openatC`.
@@ -1683,7 +1696,7 @@ pub fn renameatW(
         .dir = old_dir_fd,
         .access_mask = windows.SYNCHRONIZE | windows.GENERIC_WRITE | windows.DELETE,
         .creation = windows.FILE_OPEN,
-        .enable_async_io = false,
+        .io_mode = .blocking,
     }) catch |err| switch (err) {
         error.WouldBlock => unreachable, // Not possible without `.share_access_nonblocking = true`.
         else => |e| return e,
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index 3e55a825de..3ef3b63086 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -116,10 +116,10 @@ pub const OpenFileOptions = struct {
 /// TODO when share_access_nonblocking is false, this implementation uses
 /// untinterruptible sleep() to block. This is not the final iteration of the API.
 pub fn OpenFile(sub_path_w: []const u16, options: OpenFileOptions) OpenError!HANDLE {
-    if (sub_path_w[0] == '.' and sub_path_w[1] == 0) {
+    if (mem.eql(u16, sub_path_w, ".")) {
         return error.IsDir;
     }
-    if (sub_path_w[0] == '.' and sub_path_w[1] == '.' and sub_path_w[2] == 0) {
+    if (mem.eql(u16, sub_path_w, "..")) {
         return error.IsDir;
     }
 
diff --git a/lib/std/reset_event.zig b/lib/std/reset_event.zig
index c28db809ca..860f494f3f 100644
--- a/lib/std/reset_event.zig
+++ b/lib/std/reset_event.zig
@@ -52,7 +52,7 @@ pub const ResetEvent = struct {
 
     /// Wait for the event to be set by blocking the current thread.
     /// A timeout in nanoseconds can be provided as a hint for how
-    /// long the thread should block on the unset event before throwind error.TimedOut.
+    /// long the thread should block on the unset event before throwing error.TimedOut.
     pub fn timedWait(self: *ResetEvent, timeout_ns: u64) !void {
         return self.os_event.wait(timeout_ns);
     }