Platform SDK: DLLs, Processes, and Threads

Waiting for Multiple Objects

The following example uses the CreateEvent function to create two event objects. It then uses the WaitForMultipleObjects function to wait for the state of one of the objects to be set to signaled.

HANDLE hEvents[2]; 
DWORD i, dwEvent; 

// Create two event objects.

for (i = 0; i < 2; i++) 
{ 
    hEvents[i] = CreateEvent( 
        NULL,   // no security attributes
        FALSE,  // auto-reset event object
        FALSE,  // initial state is nonsignaled
        NULL);  // unnamed object
    if (hEvents[i] == NULL) { 
        printf("CreateEvent error: %d\n", GetLastError() ); 
        ExitProcess(0); 
    } 
} 

// The creating thread waits for other threads or processes
// to signal the event objects.

dwEvent = WaitForMultipleObjects( 
    2,           // number of objects in array
    hEvents,     // array of objects
    FALSE,       // wait for any
    INFINITE);   // indefinite wait

// Return value indicates which event is signaled.

switch (dwEvent) { 

    // hEvent[0] was signaled.
    case WAIT_OBJECT_0 + 0: 
        // Perform tasks required by this event.
        break; 

    // hEvent[1] was signaled.
    case WAIT_OBJECT_0 + 1: 
        // Perform tasks required by this event.
        break; 

    // Return value is invalid.
    default: 
        printf("Wait error: %d\n", GetLastError()); 
        ExitProcess(0); 
}