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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package sync
package func cas(val *int32, old, new int32) bool
export type Mutex struct {
key int32;
sema int32;
}
func xadd(val *int32, delta int32) (new int32) {
for {
v := *val;
if cas(val, v, v+delta) {
return v+delta;
}
}
panic("unreached")
}
func (m *Mutex) Lock() {
if xadd(&m.key, 1) == 1 {
// changed from 0 to 1; we hold lock
return;
}
sys.semacquire(&m.sema);
}
func (m *Mutex) Unlock() {
if xadd(&m.key, -1) == 0 {
// changed from 1 to 0; no contention
return;
}
sys.semrelease(&m.sema);
}
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