Win32 線程池 QueueUserWorkItem

在windows中，系統提供了QueueUserWorkItem 函數實現異步調用，這個函數相當於在線程池中建立多個用戶工作項目，跟普通線程機制一樣，線程池也有線程的同步等機制。

 

【函數原型】

BOOL WINAPI QueueUserWorkItem(
  __in          LPTHREAD_START_ROUTINE Function,
  __in          PVOID Context,
  __in          ULONG Flags
);

【參數解析】

Function 就是用戶定義的函數；

context 是PVOID指針，也是Function的參數；

Flags 表示一組標誌值，作用可通過查MSDN看到

WT_EXECUTEDEFAULT  ：工作項目放入非I/O組件得線程中。

WT_EXECUTEINIOTHREAD ：工作項目放入I/O組件的線程中，這樣的線程在I/O請求沒有完成之前不會被終止運行，防止因爲線程被終止導致I/O請求丟失。

WT_EXECUTEINPERSISTENTTHREAD ：放入永久線程池。

WT_EXECUTELONGFUNCTION  ：工作項目需要長時間的工作，系統會據此安排更多的線程。

 

【示例代碼】

#include <assert.h>
#include <Windows.h>
#include <iostream>
#include <string>
using namespace std;


DWORD WINAPI Thread1(PVOID pContext);
DWORD WINAPI Thread2(PVOID pContext);
DWORD WINAPI Thread3(PVOID pContext);

CRITICAL_SECTION g_cs;

int main(int argc, char * argv[])
{
	HANDLE hCompleteEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
	
	InitializeCriticalSection(&g_cs);

	QueueUserWorkItem(Thread1, L"I'm thread 1", WT_EXECUTEINLONGTHREAD);
	QueueUserWorkItem(Thread2, L"I'm thread 2", WT_EXECUTEINLONGTHREAD);
	QueueUserWorkItem(Thread3, L"I'm thread 3", WT_EXECUTEINLONGTHREAD);

	WaitForSingleObject(hCompleteEvent, INFINITE);

	DeleteCriticalSection(&g_cs);

	CloseHandle(hCompleteEvent);
	//getchar();

	return 0;
}
//
DWORD WINAPI Thread1(PVOID pContext)
{
	EnterCriticalSection(&g_cs);
	wchar_t * wszVal = (wchar_t*)pContext;
	wcout << L"wszVal:" << wszVal << endl;
	LeaveCriticalSection(&g_cs);

	for(int i=0; i<=50; i++)
	{
		EnterCriticalSection(&g_cs);
		cout << "One Thread Output : " << i <<endl;
		LeaveCriticalSection(&g_cs);
	}

	return 0;
}
//
DWORD WINAPI Thread2(PVOID pContext)
{
	EnterCriticalSection(&g_cs);
	wchar_t * wszVal = (wchar_t*)pContext;
	wcout << L"wszVal:" << wszVal << endl;
	LeaveCriticalSection(&g_cs);

	for(int i=0; i<=50; i++)
	{
		EnterCriticalSection(&g_cs);
		cout << "Two Thread Output : " << i <<endl;
		LeaveCriticalSection(&g_cs);
	}
	return 0;
}
//
DWORD WINAPI Thread3(PVOID pContext)
{
	EnterCriticalSection(&g_cs);
	wchar_t * wszVal = (wchar_t*)pContext;
	wcout << L"wszVal:" << wszVal << endl;
	LeaveCriticalSection(&g_cs);

	for(int i=0; i<=50; i++)
	{
		EnterCriticalSection(&g_cs);
		cout << "Three Thread Output : " << i << endl;
		LeaveCriticalSection(&g_cs);
	}
	return 0;
}