std.Mutex: implement blocking mutexes on linux

closes #1463

Thanks to Shawn Landden for the original pull request.
This commit is based on that code.

1 files changed, 32 insertions, 0 deletions

diff --git a/std/spinlock.zig b/std/spinlock.zig
new file mode 100644
index 0000000000..75fdf9f6e1
--- /dev/null
+++ b/std/spinlock.zig
@@ -0,0 +1,32 @@
+const std = @import("index.zig");
+const builtin = @import("builtin");
+const AtomicOrder = builtin.AtomicOrder;
+const AtomicRmwOp = builtin.AtomicRmwOp;
+const assert = std.debug.assert;
+
+pub const SpinLock = struct {
+    lock: u8, // TODO use a bool or enum
+
+    pub const Held = struct {
+        spinlock: *SpinLock,
+
+        pub fn release(self: Held) void {
+            assert(@atomicRmw(u8, &self.spinlock.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
+        }
+    };
+
+    pub fn init() SpinLock {
+        return SpinLock{ .lock = 0 };
+    }
+
+    pub fn acquire(self: *SpinLock) Held {
+        while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
+        return Held{ .spinlock = self };
+    }
+};
+
+test "spinlock" {
+    var lock = SpinLock.init();
+    const held = lock.acquire();
+    defer held.release();
+}