SETEVENT的使用

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 = 0; 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
0,                 // default stack size
ThreadProc,        // name of the thread function
NULL,              // no thread parameters
0,                 // 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 1;
}

// Close the events to clean up

CloseEvents();

return 0;
}

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 0;
}

// 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 1;
}

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。