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SETEVENT的使用
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来源：https://msdn.microsoft.com/en-us/library/windows/desktop/ms686915(v=vs.85).aspx
昨天看到这个SetEvent的方法，感觉很新鲜。今天记录一下
The following example uses event objects to prevent several threads from reading from a shared memory buffer while a master thread is writing to that buffer. First, the master thread uses the CreateEvent function to create a manual-reset event object whose initial state is nonsignaled. Then it creates several reader threads. The master thread performs a write operation and then sets the event object to the signaled state when it has finished writing.
Before starting a read operation, each reader thread uses WaitForSingleObject to wait for the manual-reset event object to be signaled. When WaitForSingleObject returns, this indicates that the main thread is ready for it to begin its read operation.
#include <windows.h>
#include <stdio.h> #define THREADCOUNT 4 HANDLE ghWriteEvent;
HANDLE ghThreads[THREADCOUNT]; DWORD WINAPI ThreadProc(LPVOID); void CreateEventsAndThreads(void)
{
int i;
DWORD dwThreadID; // Create a manual-reset event object. The write thread sets this
// object to the signaled state when it finishes writing to a
// shared buffer. ghWriteEvent = CreateEvent(
NULL, // default security attributes
TRUE, // manual-reset event
FALSE, // initial state is nonsignaled
TEXT("WriteEvent") // object name
); if (ghWriteEvent == NULL)
{
printf("CreateEvent failed (%d)\n", GetLastError());
return;
} // Create multiple threads to read from the buffer. for(i = ; i < THREADCOUNT; i++)
{
// TODO: More complex scenarios may require use of a parameter
// to the thread procedure, such as an event per thread to
// be used for synchronization.
ghThreads[i] = CreateThread(
NULL, // default security
, // default stack size
ThreadProc, // name of the thread function
NULL, // no thread parameters
, // default startup flags
&dwThreadID); if (ghThreads[i] == NULL)
{
printf("CreateThread failed (%d)\n", GetLastError());
return;
}
}
} void WriteToBuffer(VOID)
{
// TODO: Write to the shared buffer. printf("Main thread writing to the shared buffer...\n"); // Set ghWriteEvent to signaled if (! SetEvent(ghWriteEvent) )
{
printf("SetEvent failed (%d)\n", GetLastError());
return;
}
} void CloseEvents()
{
// Close all event handles (currently, only one global handle). CloseHandle(ghWriteEvent);
} int main( void )
{
DWORD dwWaitResult; // TODO: Create the shared buffer // Create events and THREADCOUNT threads to read from the buffer CreateEventsAndThreads(); // At this point, the reader threads have started and are most
// likely waiting for the global event to be signaled. However,
// it is safe to write to the buffer because the event is a
// manual-reset event. WriteToBuffer(); printf("Main thread waiting for threads to exit...\n"); // The handle for each thread is signaled when the thread is
// terminated.
dwWaitResult = WaitForMultipleObjects(
THREADCOUNT, // number of handles in array
ghThreads, // array of thread handles
TRUE, // wait until all are signaled
INFINITE); switch (dwWaitResult)
{
// All thread objects were signaled
case WAIT_OBJECT_0:
printf("All threads ended, cleaning up for application exit...\n");
break; // An error occurred
default:
printf("WaitForMultipleObjects failed (%d)\n", GetLastError());
return ;
} // Close the events to clean up CloseEvents(); return ;
} DWORD WINAPI ThreadProc(LPVOID lpParam)
{
// lpParam not used in this example.
UNREFERENCED_PARAMETER(lpParam); DWORD dwWaitResult; printf("Thread %d waiting for write event...\n", GetCurrentThreadId()); dwWaitResult = WaitForSingleObject(
ghWriteEvent, // event handle
INFINITE); // indefinite wait switch (dwWaitResult)
{
// Event object was signaled
case WAIT_OBJECT_0:
//
// TODO: Read from the shared buffer
//
printf("Thread %d reading from buffer\n",
GetCurrentThreadId());
break; // An error occurred
default:
printf("Wait error (%d)\n", GetLastError());
return ;
} // Now that we are done reading the buffer, we could use another
// event to signal that this thread is no longer reading. This
// example simply uses the thread handle for synchronization (the
// handle is signaled when the thread terminates.) printf("Thread %d exiting\n", GetCurrentThreadId());
return ;
}
CreateEvent，SetEvent，ResetEvent这三个方法主要是用于线程同步，和通信。
是否需要使用ResetEvent是根据CreateEvent的第二个参数而定的
TRUE, // manual-reset event。
