[Muduo网络库源码分析] (6) base/Mutex.h_互斥锁操作

互斥锁操作

功能：封装对互斥锁的操作

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知识点：

• MCHECK()宏的实现

#define MCHECK(ret) ({ __typeof__ (ret) errnum = (ret);         \                       if (__builtin_expect(errnum != 0, 0))    \                         __assert_perror_fail (errnum, __FILE__, __LINE__, __func__);})

• 线程与锁的对应关系

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用途：

可用于多线程互斥锁的操作

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亮点程序：

//对锁进行解锁，加锁操作class MutexLockGuard : boost::noncopyable{ public:  explicit MutexLockGuard(MutexLock& mutex)    : mutex_(mutex)  {    mutex_.lock();  }  ~MutexLockGuard()  {    mutex_.unlock();  } private:  MutexLock& mutex_;};

上述代码在使用过程中非常方便，其可以对作用域内的内容上锁，并实现自动解锁

{    MutexLockGuard mu = MutexLockGuard(mutex_)    ...}

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代码及分析：

Mutex.h

// Use of this source code is governed by a BSD-style license// that can be found in the License file.//// Author: Shuo Chen (chenshuo at chenshuo dot com)#ifndef MUDUO_BASE_MUTEX_H#define MUDUO_BASE_MUTEX_H#include <muduo/base/CurrentThread.h>#include <boost/noncopyable.hpp>#include <assert.h>#include <pthread.h>#ifdef CHECK_PTHREAD_RETURN_VALUE#ifdef NDEBUG//用C++编译器统一处理__BEGIN_DECLSextern void __assert_perror_fail (int errnum,                                  const char *file,                                  unsigned int line,                                  const char *function)    //无返回值    __THROW __attribute__ ((__noreturn__));__END_DECLS#endif//检查是否出错 ，__typeof__定义与ret类型相同的errnum，大多数情况下不执行if语句#define MCHECK(ret) ({ __typeof__ (ret) errnum = (ret);         \                       if (__builtin_expect(errnum != 0, 0))    \                         __assert_perror_fail (errnum, __FILE__, __LINE__, __func__);})#else  // CHECK_PTHREAD_RETURN_VALUE#define MCHECK(ret) ({ __typeof__ (ret) errnum = (ret);         \                       assert(errnum == 0); (void) errnum;})#endif // CHECK_PTHREAD_RETURN_VALUEnamespace muduo{// Use as data member of a class, eg.//// class Foo// {//  public://   int size() const;////  private://   mutable MutexLock mutex_;//   std::vector<int> data_; // GUARDED BY mutex_// };class MutexLock : boost::noncopyable{ public:  //构造函数，初始化线程ID,初始化锁  MutexLock()    : holder_(0)  {    MCHECK(pthread_mutex_init(&mutex_, NULL));  }  //析构函数，销毁锁  ~MutexLock()  {    assert(holder_ == 0);    MCHECK(pthread_mutex_destroy(&mutex_));  }  //互斥锁是否作用于当前线程  // must be called when locked, i.e. for assertion  bool isLockedByThisThread() const  {    return holder_ == CurrentThread::tid();  }  //如果不是作用于当前线程，则退出  void assertLocked() const  {    assert(isLockedByThisThread());  }  // internal usage  //上锁，并存储上锁的线程ID  void lock()  {    MCHECK(pthread_mutex_lock(&mutex_));    assignHolder();  }  //解锁，并置当前线程ID标记为0  void unlock()  {    unassignHolder();    MCHECK(pthread_mutex_unlock(&mutex_));  }  //返回锁地址  pthread_mutex_t* getPthreadMutex() /* non-const */  {    return &mutex_;  } private:  friend class Condition;  //对加锁的线程进行线程ID的改变  class UnassignGuard : boost::noncopyable  {   public:    UnassignGuard(MutexLock& owner)      : owner_(owner)    {      owner_.unassignHolder();    }    ~UnassignGuard()    {      owner_.assignHolder();    }   private:    MutexLock& owner_;  };  //对holder_置零  void unassignHolder()  {    holder_ = 0;  }  //给holder_赋值为当前线程ID  void assignHolder()  {    holder_ = CurrentThread::tid();  }  pthread_mutex_t mutex_;//互斥锁  pid_t holder_;//线程ID};// Use as a stack variable, eg.// int Foo::size() const// {//   MutexLockGuard lock(mutex_);//   return data_.size();// }//对锁进行解锁，加锁操作class MutexLockGuard : boost::noncopyable{ public:  explicit MutexLockGuard(MutexLock& mutex)    : mutex_(mutex)  {    mutex_.lock();  }  ~MutexLockGuard()  {    mutex_.unlock();  } private:  MutexLock& mutex_;};}// Prevent misuse like:// MutexLockGuard(mutex_);// A tempory object doesn't hold the lock for long!#define MutexLockGuard(x) error "Missing guard object name"#endif  // MUDUO_BASE_MUTEX_H