Implementation of mutex and condtion for Thread Synchronization in Android

Tian haili
2013-08-10

Android-encapsulated synchronization classes mainly include mutex (automutex) and condition. The previous article analyzes their external use. This article describes how they are implemented through encapsulation of pthread mutex and condition. The usage of pthread can be viewed in conjunction with the usage of mutex and condition of pthread.
Keywords: mutex, condition variable, autolock/automutex, Android
Keywords: mutex, condition variable, automatic lock/automatic mutex, Android

1. Implementation of mutex

The implementation of mutex is in frameworks/native/include/utils/mutex. h.

The implementation of mutex utilizes the implementation of pthread mutex.

First, class mutex internally defines a pthread_mutex

    pthread_mutex_t mMutex;

Then, pthread_mutex_xxx () is encapsulated respectively:

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);}

For more information about pthread mutex usage, see pthread mutex and condition usage.

II. Implementation of autolock/automutex

The implementation of autolock/automutex is also in frameworks/native/include/utils/mutex. h.

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

Iii. Implementation of Condition

Condition is implemented in frameworks/native/include/utils/condition. h.

The implementation of condition utilizes the implementation of pthread condition.

First, class condition defines a pthread_cond

    pthread_cond_t mCond;

Then, pthread_cond_xxx () is encapsulated respectively:

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);}

For more information about pthread condition usage, see pthread mutex and condition usage.

Iv. Summary

This article briefly introduces the internal implementation of the commonly used synchronization mechanism mutex (automutex) and condition in Android, that is, the simple encapsulation of pthread mutex and condition. The usage of mutex and condition in pthread is described in usage of mutex and condition in pthread.