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android分析之mutex
Android的锁是对Linux锁的一种包装:
// ---------------------------------------------------------------------------namespace android {// ---------------------------------------------------------------------------class Condition;/* * Simple mutex class. The implementation is system-dependent. * * The mutex must be unlocked by the thread that locked it. They are not * recursive, i.e. the same thread can‘t lock it multiple times. */class Mutex {public: enum { PRIVATE = 0,//该锁为本进程内使用 SHARED = 1//该锁跨进程使用 }; Mutex(); Mutex(const char* name); Mutex(int type, const char* name = NULL); ~Mutex(); // lock or unlock the mutex status_t lock(); void unlock(); // lock if possible; returns 0 on success, error otherwise status_t tryLock(); // Manages the mutex automatically. It‘ll be locked when Autolock is // constructed and released when Autolock goes out of scope. class Autolock {//内部类,用来管理mutex的--相当于“智能指针” public: inline Autolock(Mutex& mutex) : mLock(mutex) { mLock.lock(); } inline Autolock(Mutex* mutex) : mLock(*mutex) { mLock.lock(); } inline ~Autolock() { mLock.unlock(); } private: Mutex& mLock;//持有mutex的引用 };private: friend class Condition;//友元类,Condition是在mutex的基础上使用的 // A mutex cannot be copied Mutex(const Mutex&);//设为私有,无法调用“拷贝构造函数” Mutex& operator = (const Mutex&); #if defined(HAVE_PTHREADS) pthread_mutex_t mMutex;//使用linux的pthread_mutex_t这个互斥锁#else void _init(); void* mState;#endif};// ---------------------------------------------------------------------------#if defined(HAVE_PTHREADS)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) {//if分支:根据传进来的值,决定是否构造“跨进程”的锁 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);//if分支:本进程内的锁 }}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);}#endif // HAVE_PTHREADS// ---------------------------------------------------------------------------/* * Automatic mutex. Declare one of these at the top of a function. * When the function returns, it will go out of scope, and release the * mutex. */ typedef Mutex::Autolock AutoMutex;// ---------------------------------------------------------------------------}; // namespace android
android分析之mutex
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