59 lines
1.6 KiB
Go
59 lines
1.6 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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// Package sync provides basic synchronization primitives such as mutual
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// exclusion locks. Other than the Once and WaitGroup types, most are intended
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// for use by low-level library routines. Higher-level synchronization is
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// better done via channels and communication.
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package sync
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import (
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"runtime"
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"sync/atomic"
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)
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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 int32
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sema uint32
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}
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// A Locker represents an object that can be locked and unlocked.
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type Locker interface {
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Lock()
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Unlock()
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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 atomic.AddInt32(&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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switch v := atomic.AddInt32(&m.key, -1); {
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case v == 0:
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// changed from 1 to 0; no contention
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return
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case v == -1:
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// changed from 0 to -1: wasn't locked
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// (or there are 4 billion goroutines waiting)
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panic("sync: unlock of unlocked mutex")
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}
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runtime.Semrelease(&m.sema)
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}
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