Muduo库源码分析（5）：互斥锁，条件变量类

1. 互斥锁（muduo库简单的封装）
   将muduo库的线程id的操作去除的简单版本

// 出错处理#define MCHECK(ret) ({ __typeof__ (ret) errnum = (ret); assert(errnum == 0); (void) errnum;})class MutexLock : noncopyable{ public:  MutexLock()  {  // 初始化互斥锁    MCHECK(pthread_mutex_init(&mutex_, NULL));  }  ~MutexLock()  {  // 销毁互斥锁    MCHECK(pthread_mutex_destroy(&mutex_));  }  void lock()  {  // 加锁    MCHECK(pthread_mutex_lock(&mutex_));  }  void unlock()  {  // 解锁    MCHECK(pthread_mutex_unlock(&mutex_));  }  pthread_mutex_t* getPthreadMutex()   {  // 获取锁    return &mutex_;  } private:  pthread_mutex_t mutex_;// 互斥锁};// 对加锁和解锁操作进行封装，采用的是C++的RAII机制，好处是不需要手动进行解锁操作，由MutexLockGuard类自动管理解锁操作（析构函数完成）。链接：[http://www.cnblogs.com/gnuhpc/archive/2012/12/04/2802307.html "C++ RAII机制"]class MutexLockGuard : noncopyable{ public:  explicit MutexLockGuard(MutexLock& mutex)    : mutex_(mutex)  {    mutex_.lock();  }  ~MutexLockGuard()  {    mutex_.unlock();  } private:  MutexLock& mutex_;// 采用的是引用，目的是该类只负责加锁和解锁，而互斥量的销毁由MutexLock类负责 };// 阻止匿名互斥量的操作#define MutexLockGuard(x) error "Missing guard object name"

1. 条件变量类封装

 class Condition : noncopyable{ public:  explicit Condition(MutexLock& mutex)    : mutex_(mutex)  {  // 条件变量初始化    MCHECK(pthread_cond_init(&pcond_, NULL));  }  ~Condition()  {  // 消除条件变量    MCHECK(pthread_cond_destroy(&pcond_));  }  void wait()  {MCHECK(pthread_cond_wait(&pcond_,mutex_.getPthreadMutex()));  } void notify()  {    MCHECK(pthread_cond_signal(&pcond_));  }  void notifyAll()  {    MCHECK(pthread_cond_broadcast(&pcond_));  } bool waitForSeconds(double seconds) { struct timespec abstime;  clock_gettime(CLOCK_REALTIME, &abstime);  const int64_t kNanoSecondsPerSecond = 1e9;  int64_t nanoseconds = static_cast<int64_t>(seconds * kNanoSecondsPerSecond);  abstime.tv_sec += static_cast<time_t>((abstime.tv_nsec + nanoseconds) / kNanoSecondsPerSecond);  abstime.tv_nsec = static_cast<long>((abstime.tv_nsec + nanoseconds) % kNanoSecondsPerSecond);  MutexLock::UnassignGuard ug(mutex_);  return ETIMEDOUT == pthread_cond_timedwait(&pcond_, mutex_.getPthreadMutex(), &abstime); } private:  MutexLock& mutex_;// 互斥量  pthread_cond_t pcond_;// 条件变量};

1. CountDownLatch类：
   可实现子进程等待主进程发起命令后竞争执行
   （主线程调用countDown,子线程调用wait）
   也可实现主线程等待子进程初始化完成后在执行
   （主线程调用wait,子线程调用countDown）

class CountDownLatch : noncopyable{ public:  explicit CountDownLatch(int count);  void wait()  {   MutexLockGuard lock(mutex_); // 加锁  while (count_ > 0)// 等待条件  {    condition_.wait();// 等待  }  }  void countDown()  {   MutexLockGuard lock(mutex_);  --count_;  if (count_ == 0)  {    condition_.notifyAll();  }  }  int getCount() const  {  MutexLockGuard lock(mutex_);  return count_;  } private:  mutable MutexLock mutex_;// 声明为mutable的目的是因为getCount函数声明为const函数而该函数会改变锁的状态  Condition condition_;  int count_;};