zig

commit de949b72c791477c29155ee09a1c5c3d4ab56033 (tree)
parent 058bfb254c4c0e1cfb254791f771c88c74f299e8
Author: Andrew Kelley <superjoe30@gmail.com>
Date:   Tue, 31 Jul 2018 19:57:46 -0400

simpler std.event.Lock implementation

Diffstat:
M
std/event/lock.zig
 | 
27
++-------------------------

1 file changed, 2 insertions(+), 25 deletions(-)
diff --git a/std/event/lock.zig b/std/event/lock.zig
@@ -106,35 +106,12 @@ pub const Lock = struct {
             // will attempt to grab the lock.
             _ = @atomicRmw(u8, &self.queue_empty_bit, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst);
 
-            while (true) {
-                const old_bit = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
-                if (old_bit != 0) {
-                    // We did not obtain the lock. Trust that our queue entry will resume us, and allow
-                    // suspend to complete.
-                    break;
-                }
-                // We got the lock. However we might have already been resumed from the queue.
+            const old_bit = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
+            if (old_bit == 0) {
                 if (self.queue.get()) |node| {
                     // Whether this node is us or someone else, we tail resume it.
                     resume node.data;
-                    break;
-                } else {
-                    // We already got resumed, and there are none left in the queue, which means that
-                    // we aren't even supposed to hold the lock right now.
-                    _ = @atomicRmw(u8, &self.queue_empty_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
-                    _ = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst);
-
-                    // There might be a queue item. If we know the queue is empty, we can be done,
-                    // because the other actor will try to obtain the lock.
-                    // But if there's a queue item, we are the actor which must loop and attempt
-                    // to grab the lock again.
-                    if (@atomicLoad(u8, &self.queue_empty_bit, AtomicOrder.SeqCst) == 1) {
-                        break;
-                    } else {
-                        continue;
-                    }
                 }
-                unreachable;
             }
         }