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// Copyright 2019 The gVisor Authors.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build go1.13
// +build !go1.17
// When updating the build constraint (above), check that syncMutex matches the
// standard library sync.Mutex definition.
package sync
import (
"sync"
"sync/atomic"
"unsafe"
)
// CrossGoroutineMutex is equivalent to Mutex, but it need not be unlocked by a
// the same goroutine that locked the mutex.
type CrossGoroutineMutex struct {
sync.Mutex
}
type syncMutex struct {
state int32
sema uint32
}
func (m *CrossGoroutineMutex) state() *int32 {
return &(*syncMutex)(unsafe.Pointer(&m.Mutex)).state
}
const (
mutexUnlocked = 0
mutexLocked = 1
)
// TryLock tries to acquire the mutex. It returns true if it succeeds and false
// otherwise. TryLock does not block.
func (m *CrossGoroutineMutex) TryLock() bool {
if atomic.CompareAndSwapInt32(m.state(), mutexUnlocked, mutexLocked) {
if RaceEnabled {
RaceAcquire(unsafe.Pointer(&m.Mutex))
}
return true
}
return false
}
// Mutex is a mutual exclusion lock. The zero value for a Mutex is an unlocked
// mutex.
//
// A Mutex must not be copied after first use.
//
// A Mutex must be unlocked by the same goroutine that locked it. This
// invariant is enforced with the 'checklocks' build tag.
type Mutex struct {
m CrossGoroutineMutex
}
// Lock locks m. If the lock is already in use, the calling goroutine blocks
// until the mutex is available.
func (m *Mutex) Lock() {
noteLock(unsafe.Pointer(m))
m.m.Lock()
}
// Unlock unlocks m.
//
// Preconditions:
// * m is locked.
// * m was locked by this goroutine.
func (m *Mutex) Unlock() {
noteUnlock(unsafe.Pointer(m))
m.m.Unlock()
}
// TryLock tries to acquire the mutex. It returns true if it succeeds and false
// otherwise. TryLock does not block.
func (m *Mutex) TryLock() bool {
// Note lock first to enforce proper locking even if unsuccessful.
noteLock(unsafe.Pointer(m))
locked := m.m.TryLock()
if !locked {
noteUnlock(unsafe.Pointer(m))
}
return locked
}
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