windows 下 信号量使用示例 

  1 #include <stdio.h>
  2 #include <Windows.h> 
  3 
  4 #define MAX_SEM_COUNT 10
  5 #define THREADCOUNT 12
  6 
  7 HANDLE ghSemaphore;
  8 DWORD WINAPI ThreadProc( LPVOID );
  9 
 10 void main(int argc, char* argv[])
 11 {
 12     HANDLE aThread[THREADCOUNT];
 13     DWORD ThreadID;
 14     int i;
 15 
 16     // Create a semaphore with initial and max counts of MAX_SEM_COUNT
 17     ghSemaphore = CreateSemaphore( 
 18         NULL,           // default security attributes - lpSemaphoreAttributes是信号量的安全属性
 19         MAX_SEM_COUNT,  // initial count - lInitialCount是初始化的信号量
 20         MAX_SEM_COUNT,  // maximum count - lMaximumCount是允许信号量增加到最大值
 21         NULL);          // unnamed semaphore - lpName是信号量的名称
 22 
 23     if (ghSemaphore == NULL) 
 24     {
 25         printf("CreateSemaphore error: %d\n", GetLastError());
 26         return;
 27     }
 28 
 29     // Create worker threads
 30     for( i=0; i <THREADCOUNT; i++ )
 31     {
 32         aThread[i] = CreateThread( 
 33             NULL,       // default security attributes
 34             0,          // default stack size
 35             (LPTHREAD_START_ROUTINE) ThreadProc, 
 36             NULL,       // no thread function arguments
 37             0,          // default creation flags
 38             &ThreadID); // receive thread identifier
 39 
 40         if( aThread[i] == NULL )
 41         {
 42             printf("CreateThread error: %d\n", GetLastError());
 43             return;
 44         }
 45     }
 46 
 47     // Wait for all threads to terminate
 48     WaitForMultipleObjects(THREADCOUNT, aThread, TRUE, INFINITE);
 49 
 50     // Close thread and semaphore handles
 51     for( i=0; i <THREADCOUNT; i++ )
 52         CloseHandle(aThread[i]);
 53 
 54     CloseHandle(ghSemaphore); 
 55 }
 56 
 57 DWORD WINAPI ThreadProc( LPVOID lpParam )
 58 {
 59     DWORD dwWaitResult;
 60     BOOL bContinue=TRUE;
 61 
 62     while(bContinue)
 63     {
 64         // Try to enter the semaphore gate.
 65         dwWaitResult = WaitForSingleObject( 
 66             ghSemaphore,   // handle to semaphore
 67             0L);           // zero-second time-out interval
 68 
 69         switch (dwWaitResult) 
 70         { 
 71             // The semaphore object was signaled.
 72         case WAIT_OBJECT_0: 
 73             // TODO: Perform task
 74             printf("Thread %d: wait succeeded\n", GetCurrentThreadId());
 75             
 76             // Ensure a thread performs only once
 77             bContinue=FALSE;
 78 
 79             // Simulate thread spending time on task
 80             Sleep(5);
 81 
 82             // Release the semaphore when task is finished
 83 
 84             if (!ReleaseSemaphore( 
 85                 ghSemaphore,  // handle to semaphore - hSemaphore是要增加的信号量句柄
 86                 1,            // increase count by one - lReleaseCount是增加的计数
 87                 NULL) )       // not interested in previous count - lpPreviousCount是增加前的数值返回
 88             {
 89                 printf("ReleaseSemaphore error: %d\n", GetLastError());
 90             }
 91             break;
 92 
 93             // The semaphore was nonsignaled, so a time-out occurred.
 94         case WAIT_TIMEOUT: 
 95             printf("Thread %d: wait timed out\n", GetCurrentThreadId());
 96             break; 
 97         }
 98     }
 99     return TRUE;
100 }

posted @ 2011-04-26 15:24  fanopi  阅读(1859)  评论(0)    收藏  举报