Android中线程同步之MUTEX与Condtion的实现

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田海立
2013-08-10

Android封装的同步类主要有MUTEX（AutoMutex）与Condition。前文分析了它们的外部使用，本文看它们是如何通过对pthread Mutex和Condition的封装实现的。遇到pthread的用法，可结合《 pthread之MUTEX与Condition用法》一起看。
Keywords: Mutex, Condition Variable, AutoLock/AutoMutex, Android
关键字：互斥体、条件变量、自动锁/自动互斥体、Android

一、MUTEX的实现

MUTEX的实现是在frameworks/native/include/utils/Mutex.h中。

Mutex的实现利用了pthread Mutex的实现。

首先，Class Mutex内部定义一个pthread_mutex

    pthread_mutex_t mMutex;

然后，分别封装了pthread_mutex_xxx()而已：

inline Mutex::Mutex() {pthread_mutex_init(&mMutex, NULL);
}
inline Mutex::Mutex(const char* name) {pthread_mutex_init(&mMutex, NULL);
}
inline Mutex::Mutex(int type, const char* name) {if (type == SHARED) {pthread_mutexattr_t attr;pthread_mutexattr_init(&attr);pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);pthread_mutex_init(&mMutex, &attr);pthread_mutexattr_destroy(&attr);} else {pthread_mutex_init(&mMutex, NULL);}
}
inline Mutex::~Mutex() {pthread_mutex_destroy(&mMutex);
}
inline status_t Mutex::lock() {return -pthread_mutex_lock(&mMutex);
}
inline void Mutex::unlock() {pthread_mutex_unlock(&mMutex);
}
inline status_t Mutex::tryLock() {return -pthread_mutex_trylock(&mMutex);
}

具体pthread Mutex的用法，参见《pthread之MUTEX与Condition用法》

二、Autolock/AutoMutex的实现

Autolock/AutoMutex的实现同样是在frameworks/native/include/utils/Mutex.h中。

namespace android {class Mutex {//...class Autolock {public:inline Autolock(Mutex& mutex) : mLock(mutex)  { mLock.lock(); }inline Autolock(Mutex* mutex) : mLock(*mutex) { mLock.lock(); }inline ~Autolock() { mLock.unlock(); }private:Mutex& mLock;};}; // end of class Mutextypedef Mutex::Autolock AutoMutex;}; // namespace android

三、Condition的实现

Condition的实现是在frameworks/native/include/utils/Condition.h中

Condition的实现利用了pthread Condition的实现。

首先，Class Condition内定义一个pthread_cond

    pthread_cond_t mCond;

然后，分别封装了pthread_cond_xxx()而已：

inline Condition::Condition() {pthread_cond_init(&mCond, NULL);
}
inline Condition::Condition(int type) {if (type == SHARED) {pthread_condattr_t attr;pthread_condattr_init(&attr);pthread_condattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);pthread_cond_init(&mCond, &attr);pthread_condattr_destroy(&attr);} else {pthread_cond_init(&mCond, NULL);}
}
inline Condition::~Condition() {pthread_cond_destroy(&mCond);
}
inline status_t Condition::wait(Mutex& mutex) {return -pthread_cond_wait(&mCond, &mutex.mMutex);
}
inline void Condition::signal() {pthread_cond_signal(&mCond);
}
inline void Condition::broadcast() {pthread_cond_broadcast(&mCond);
}

具体pthread Condition的用法，参见《pthread之MUTEX与Condition用法》