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* Copyright 2013 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkMutex_pthread_DEFINED
#define SkMutex_pthread_DEFINED
/** Posix pthread_mutex based mutex. */
#include <errno.h>
#include <pthread.h>
// We use error-checking mutexes in Debug builds or normal fast mutexes in Release builds.
// Debug builds get these checks for free:
// - a double acquire() from the same thread fails immediately instead of deadlocking;
// - release() checks that the mutex is being unlocked by its owner thread.
// I don't see a built-in way to implement assertHeld(), so we track that with an fOwner field.
// This isn't technically portable, but on Linux and Android pthread_t is some sort of int, and
// on Darwin it's a pointer. So assuming pthread_self() never returns 0, it works as a sentinel.
SkDEBUGCODE(static const pthread_t kNoOwner = 0;)
// An SkBaseMutex is a POD structure that can be directly initialized at declaration time with
// SK_DECLARE_STATIC_MUTEX. This avoids the generation of a static initializer in the final
// machine code (and a corresponding static finalizer).
struct SkBaseMutex {
void acquire() {
SkDEBUGCODE(int rc = ) pthread_mutex_lock(&fMutex);
SkASSERT(0 == rc);
SkDEBUGCODE(fOwner = pthread_self();)
void release() {
this->assertHeld(); // Usually redundant, but not for static mutexes on Macs (see below).
SkDEBUGCODE(fOwner = kNoOwner;)
SkDEBUGCODE(int rc = ) pthread_mutex_unlock(&fMutex);
SkASSERT(0 == rc);
void assertHeld() {
SkASSERT(0 != pthread_equal(fOwner, pthread_self()));
pthread_mutex_t fMutex;
SkDEBUGCODE(pthread_t fOwner;) // Read and write only when holding fMutex.
// A normal mutex that's required to be initialized through normal C++ construction,
// i.e. when it's a member of another class, or allocated on the heap.
class SkMutex : public SkBaseMutex {
SkMutex() {
#ifdef SK_DEBUG
pthread_mutexattr_t attr;
SkASSERT(0 == pthread_mutexattr_init(&attr));
SkASSERT(0 == pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK));
SkASSERT(0 == pthread_mutex_init(&fMutex, &attr));
SkASSERT(0 == pthread_mutexattr_destroy(&attr));
fOwner = kNoOwner;
(void)pthread_mutex_init(&fMutex, NULL);
~SkMutex() {
SkDEBUGCODE(int rc = )pthread_mutex_destroy(&fMutex);
SkASSERT(0 == rc);
SkMutex(const SkMutex&);
SkMutex& operator=(const SkMutex&);
// When possible we want to use error-check mutexes in Debug builds. See the note at the top.
#elif defined(SK_DEBUG)
// Macs don't support PTHREAD_ERRORCHECK_MUTEX_INITIALIZER when targeting <10.7. We target 10.6.
// Using POD-style initialization prevents the generation of a static initializer.
// Without magic statics there are no thread safety guarantees on initialization
// of local statics (even POD). As a result, it is illegal to use
// SK_DECLARE_STATIC_MUTEX in a function.
// Because SkBaseMutex is not a primitive, a static SkBaseMutex cannot be
// initialized in a class with this macro.
#define SK_DECLARE_STATIC_MUTEX(name) namespace {} static SkBaseMutex name = SK_BASE_MUTEX_INIT