62 lines
1.7 KiB
Go
62 lines
1.7 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// The sync package provides basic synchronization primitives
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// such as mutual exclusion locks. Other than the Once type,
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// most are intended for use by low-level library routines.
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// Higher-level synchronization is better done via channels
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// and communication.
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package sync
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import "runtime"
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func cas(val *uint32, old, new uint32) bool
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// A Mutex is a mutual exclusion lock.
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// Mutexes can be created as part of other structures;
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// the zero value for a Mutex is an unlocked mutex.
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type Mutex struct {
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key uint32
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sema uint32
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}
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// Add delta to *val, and return the new *val in a thread-safe way. If multiple
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// goroutines call xadd on the same val concurrently, the changes will be
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// serialized, and all the deltas will be added in an undefined order.
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func xadd(val *uint32, delta int32) (new uint32) {
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for {
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v := *val
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nv := v + uint32(delta)
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if cas(val, v, nv) {
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return nv
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}
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}
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panic("unreached")
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}
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// Lock locks m.
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// If the lock is already in use, the calling goroutine
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// blocks until the mutex is available.
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func (m *Mutex) Lock() {
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if xadd(&m.key, 1) == 1 {
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// changed from 0 to 1; we hold lock
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return
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}
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runtime.Semacquire(&m.sema)
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}
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// Unlock unlocks m.
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// It is a run-time error if m is not locked on entry to Unlock.
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//
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// A locked Mutex is not associated with a particular goroutine.
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// It is allowed for one goroutine to lock a Mutex and then
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// arrange for another goroutine to unlock it.
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func (m *Mutex) Unlock() {
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if xadd(&m.key, -1) == 0 {
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// changed from 1 to 0; no contention
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return
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}
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runtime.Semrelease(&m.sema)
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}
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