線程池函數允許我們做：
1.以異步方式調用函數??//工作項
2.每隔一段時間調用一個函數?//計時項
3.在內核對象觸發時調用一個函數?//等待項
4.在異步I/O請求完成時調用一個函數 //I/O項

2.每隔一段時間調用一個函數
如果兩個：周期的每隔5-7秒執行一段代碼，周期的每隔6-8秒執行一段代碼。
不用線程池將有兩個線程執行，上下文切換不好，如用線程池，系統可能選擇6秒間隔只喚醒一個線程執行這兩段代碼。

3.在內核對象觸發時調用一個函數
同上類似，各個線程WaitForSingleObject各自的內核對象，如用線程池用一個線程WaitForMultipleObjects 最多MAXIMUM_WAIT_OBJECTS個內核對象
一旦回調函數被調用過，必須SetThreadpoolWait再注冊下，否則 等待項 是不活躍狀態不會再調用回調函數

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#include <Windows.h>// C RunTime Header Files #include <string>PTP_WORK g_pWorkItem = NULL; volatile LONG g_nCurrentTask = 0;void NTAPI TaskHandler(PTP_CALLBACK_INSTANCE Instance, PVOID Context, PTP_WORK Work) {LONG currentTask = InterlockedIncrement(&g_nCurrentTask);wprintf(L"[%u] Task #%u is starting.\n", GetCurrentThreadId(), currentTask);// Simulate a lot of workSleep(currentTask * 1000);wprintf(L"[%u] Task #%u is done.\n", GetCurrentThreadId(), currentTask);InterlockedDecrement(&g_nCurrentTask); }void Work(void) {// Create the work item that will be used by all tasks//(1)create 線程池工作項g_pWorkItem = CreateThreadpoolWork(TaskHandler, NULL, NULL);if (g_pWorkItem == NULL) {wprintf(L"Impossible to create the work item for tasks.\n");return;}wprintf(L"----Start a new batch----\n");for(int i = 4; i > 0; --i){//(2)submit workSubmitThreadpoolWork(g_pWorkItem);}wprintf(L"4 tasks are submitted.\n");//Waits for outstanding work callbacks to complete and optionally cancels pending callbacks that have not yet started to execute.//(3)wait for work overWaitForThreadpoolWorkCallbacks(g_pWorkItem,FALSE);// Don't forget to delete the work item//(4)delete work itemCloseThreadpoolWork(g_pWorkItem); }PTP_TIMER g_timer = NULL; volatile LONG g_nSecLeft = 10; VOID CALLBACK TimeoutCallback(PTP_CALLBACK_INSTANCE pInst, PVOID pvContext, PTP_TIMER pTimer) {LONG current = InterlockedDecrement(&g_nSecLeft);if(current == 0){SetThreadpoolTimer(g_timer,NULL,0,0); //pftDueTime為NULL時，將停止調用定時器函數wprintf(L"time out----\n");}else{wprintf(L"[%u] call timer callback function #%u is left.\n", GetCurrentThreadId(), current);} }void Timer(void) {g_timer = CreateThreadpoolTimer(TimeoutCallback,NULL,NULL);// Start the timer in one second to trigger every 1 secondULARGE_INTEGER ulRelativeStartTime;ulRelativeStartTime.QuadPart = (LONGLONG) -1; // start nowFILETIME ftRelativeStartTime;ftRelativeStartTime.dwHighDateTime = ulRelativeStartTime.HighPart;ftRelativeStartTime.dwLowDateTime = ulRelativeStartTime.LowPart;SetThreadpoolTimer(g_timer, &ftRelativeStartTime, 1000, // Triggers every 1000 millisecondsINFINITE//0);//WaitForThreadpoolTimerCallbacks(g_timer,FALSE); //Why this will fail？getchar();CloseThreadpoolTimer(g_timer); }VOID NTAPI pttwaitcallback(_Inout_ PTP_CALLBACK_INSTANCE Instance,_Inout_opt_ PVOID Context,_Inout_ PTP_WAIT Wait,_In_ TP_WAIT_RESULT WaitResult) {wprintf(L"waitResult is WAIT_OBJECT_0 + %d.\n",WaitResult); }void WaitKernelObject() {PTP_WAIT pwait = CreateThreadpoolWait(pttwaitcallback,NULL,NULL);HANDLE hEvent1 = CreateEventW(NULL,FALSE,FALSE,L"event1");HANDLE hEvent2 = CreateEventW(NULL,FALSE,FALSE,L"event2");SetThreadpoolWait(pwait,hEvent1,NULL);SetEvent(hEvent1); //here will make pwait 不活躍狀態， 此狀態不會再去調回調函數。getchar();SetThreadpoolWait(pwait,hEvent2,NULL); //不活躍狀態后需要重新設置SetEvent(hEvent2);//WaitForThreadpoolWaitCallbacks(pwait,FALSE);getchar();CloseThreadpoolWait(pwait); } int wmain() {//Work();Timer();//WaitKernelObject();wprintf(L"it is over\n");getchar();return(0); }

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