AutoMutex

Android里的C++代码经常会看到AutoMutex _l(mLock);

AutoMutex其实就是Thread的一种自动的互斥锁，定义在framework/base/include/utils/thread.h中；

/*
* 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;

Autolock是Mutex的内嵌类（Java叫内部类），

// Manages the mutex automatically. It'll be locked when Autolock is
// constructed and released when Autolock goes out of scope.
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;
};

看红色部分的注释就明白了，在函数代码中使用 AutoMutex 就可以锁定对象，而代码执行完AutoMutex所在的代码域之后，就自动释放锁，它的原理是充分的利用了c++的构造和析构函数~