ACE_Condition使用

       不知道ACE怎么才能学好，感觉好复杂好抽象,，也不懂设计模式。。

       ACE_Condition是针对OS条件变量原语的包装类。条件变量不是被用作互斥原语，而是用作特定条件已经满足的指示器。

       ACE_Condition<ACE_Thread_Mutex> cond(ACE_Thread_Mutex);

       需要特别注意的是，在阻塞在wait调用中之前，条件变量机制（ACE_Cond）负责释放全局资源的互斥体（使用ACE_Thread::join()调用可以使主线程等待其他的线程结束，条件变量也可以实现）。

       条件变量不是用于互斥，而是用于我们所描述的发送信号功能。（除了ACE_Condition类，ACE还包括ACE_Condition_Thread_Mutex类，它使用ACE_Thread_Mutex作为全局资源的底层锁定机制），比如将下面work线程中的锁（acquire，release）机制去掉，就会打印出多个线程都认为自己是最后一个线程。如果信号signal去掉，wait就会一直阻塞下去。网上部分人理解是错的，ACE明确指出条件变量不是用于互斥。

#include "ace/Thread.h"#include "ace/Synch.h"#include <QtCore/QCoreApplication>static int number = 0;static int seed = 0;class Args{public:Args(ACE_Condition<ACE_Thread_Mutex> *cond,int threads):  cond_(cond),threads_(threads) {}  ACE_Condition<ACE_Thread_Mutex> *cond_;  int threads_;};static void *worker(void *arguments){Args *arg = (Args*)arguments;ACE_DEBUG((LM_DEBUG,"Thread (%t) Created to do some work\n"));arg->cond_->mutex().acquire();::number++;//workACE_OS::sleep(ACE_OS::rand() % 2);//exiting nowACE_DEBUG((LM_DEBUG,"Thread (%t) Done ! The Number is now: %d\n",number));//if all threads are done signal main thread that program can now exitif(number == arg->threads_){ACE_DEBUG((LM_DEBUG,"Last Thread ! All threads have done their job. Signal main thread.\n"));arg->cond_->signal();}arg->cond_->mutex().release();return 0;}int main(int argc, char *argv[]){int n_threads = 4;//Setup the random number generatorACE_OS::srand(::seed);//setup arguments for threadsACE_Thread_Mutex mutex;ACE_Condition<ACE_Thread_Mutex> cond(mutex);Args arg(&cond,n_threads);//spawn off n_threads number of threadsfor(int i = 0; i < n_threads; i ++){if(ACE_Thread::spawn((ACE_THR_FUNC)worker,(void*)&arg,THR_DETACHED | THR_NEW_LWP) == -1){ACE_DEBUG((LM_DEBUG,"Error in spawning thread.\n"));}}//wait for signal indicating that all threads are done and program//can exit. the global resource here is "number" and the condition//that the condition variable is waiting for is number == n_threads.mutex.acquire();while(number != n_threads){cond.wait();}mutex.release();ACE_DEBUG((LM_DEBUG,"(%t) Main thread got signal. Program exiting...\n"));ACE_OS::exit(0);return 0;}