| ... | ... | @@ -106,35 +106,12 @@ pub const Lock = struct { |
| 106 | 106 | // will attempt to grab the lock. |
| 107 | 107 | _ = @atomicRmw(u8, &self.queue_empty_bit, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst); |
| 108 | 108 | |
| 109 | | while (true) { |
| 110 | | const old_bit = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst); |
| 111 | | if (old_bit != 0) { |
| 112 | | // We did not obtain the lock. Trust that our queue entry will resume us, and allow |
| 113 | | // suspend to complete. |
| 114 | | break; |
| 115 | | } |
| 116 | | // We got the lock. However we might have already been resumed from the queue. |
| 109 | const old_bit = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst); |
| 110 | if (old_bit == 0) { |
| 117 | 111 | if (self.queue.get()) |node| { |
| 118 | 112 | // Whether this node is us or someone else, we tail resume it. |
| 119 | 113 | resume node.data; |
| 120 | | break; |
| 121 | | } else { |
| 122 | | // We already got resumed, and there are none left in the queue, which means that |
| 123 | | // we aren't even supposed to hold the lock right now. |
| 124 | | _ = @atomicRmw(u8, &self.queue_empty_bit, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst); |
| 125 | | _ = @atomicRmw(u8, &self.shared_bit, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst); |
| 126 | | |
| 127 | | // There might be a queue item. If we know the queue is empty, we can be done, |
| 128 | | // because the other actor will try to obtain the lock. |
| 129 | | // But if there's a queue item, we are the actor which must loop and attempt |
| 130 | | // to grab the lock again. |
| 131 | | if (@atomicLoad(u8, &self.queue_empty_bit, AtomicOrder.SeqCst) == 1) { |
| 132 | | break; |
| 133 | | } else { |
| 134 | | continue; |
| 135 | | } |
| 136 | 114 | } |
| 137 | | unreachable; |
| 138 | 115 | } |
| 139 | 116 | } |
| 140 | 117 | |
Andrew Kelley <andrew@ziglang.org> 2018-07-31 19:57:46-04:00
std