把window線程間傳送消息仔細的看了一遍，覺得以前的理解很不深刻。說一說對PostThreadMessage的理解。
PostThreadMessage是一個線程體發送一個消息到指定的線程ID，其原型如下：
BOOL PostThreadMessage(
DWORD idThread,
UINT Msg,
WPARAM wParam,
LPARAM lParam
);
這個函數既可以發送消息給工作線程，也可以發送給UI線程。接受PostThreadMessage的線程必須已經有了一個message queue，否則調用PostThreadMessage會失敗。因爲此原因使用GetLastError會得到錯誤碼爲1444，這種情況經常出現，解決方法有如下兩種：
1. 調用PostThreadMessage，如果失敗，就Sleep一段時間再次調用PostThreadMessage直到調用成功；
2. 創建一個Event對象，讓PostThreadMessage等待接受的線程創建一個message queue。可以通過調用PeekMessage強制系統創建一個message queue。示例代碼如下：
假設mainAPP是發送線程ThreadA是接受線程
/*mainAPP.cpp*/
……
hStartEvent = ::CreateEvent(0,FALSE,FALSE,0); //create thread start event
if(hStartEvent == 0)
{
printf("create start event failed,errno:%d\n",::GetLastError());
return 1;
}
::WaitForSingleObject(hStartEvent,INFINITE);
CloseHandle(hStartEvent);
if(!PostThreadMessage(threadaID, WM_MESSAGE_A,0,0))
{
_tprintf(_T("post error! %d\n"), GetLastError());
return 1;
}
……
ThreadA是接受線程
/* ThreadA */
MSG msg;
PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE);
if(!SetEvent(hStartEvent))
{
printf("set event error,%d\n",GetLastError());
return 1;
}
while(true){
if(GetMessage(&msg, 0,0,0)) {
switch(msg.message){
case WM_MESSAGE_A:
……
break;
}
}
}
}
PostThreadMessage傳遞的消息如果要包含信息，要注意在結束的時候釋放消息中的信息。在消息中附加信息方法如下
/*構造信息如下*/
char* pInfo = new char[MAX_INFO_SIZE]; //create dynamic msg
sprintf(pInfo,"msg_%d",++count);
PostThreadMessage(nThreadID,MY_MSG,(WPARAM)pInfo,0)//post thread msg
/*解釋信息如下*/
if(GetMessage(&msg,0,0,0)) //get msg from message queue
{
switch(msg.message)
{
case MY_MSG:
char * pInfo = (char *)msg.wParam;
printf("recv %s\n",pInfo);
delete[] pInfo; //這裏釋放了資源
break;
}
}
做了一個簡單的消息通信實驗，讓主線程中等待用戶輸入，產生不同的消息，並把這些消息post給子線程，子線程根據產生的消息做出不同的反映。這些子線程可以是工作線程也可以是UI線程。
| #include <windows.h> #include <cstdio> #include <process.h> #define MY_MSG WM_USER+100 const int MAX_INFO_SIZE = 20; HANDLE hStartEvent; // thread start event // thread function unsigned __stdcall fun(void *param) { printf("thread fun start  \n");MSG msg; PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE); if(!SetEvent(hStartEvent)) //set thread start event { printf("set start event failed,errno:%d\n",::GetLastError()); return 1; } while(true) { if(GetMessage(&msg,0,0,0)) //get msg from message queue { switch(msg.message) { case MY_MSG: char * pInfo = (char *)msg.wParam; printf("recv %s\n",pInfo); delete[] pInfo; break; } } }; return 0; } int main() { HANDLE hThread; unsigned nThreadID; hStartEvent = ::CreateEvent(0,FALSE,FALSE,0); //create thread start event if(hStartEvent == 0) { printf("create start event failed,errno:%d\n",::GetLastError()); return 1; } //start thread hThread = (HANDLE)_beginthreadex( NULL, 0, &fun, NULL, 0, &nThreadID ); if(hThread == 0) { printf("start thread failed,errno:%d\n",::GetLastError()); CloseHandle(hStartEvent); return 1; } //wait thread start event to avoid PostThreadMessage return errno:1444 ::WaitForSingleObject(hStartEvent,INFINITE); CloseHandle(hStartEvent); int count = 0; while(true) { char* pInfo = new char[MAX_INFO_SIZE]; //create dynamic msg sprintf(pInfo,"msg_%d",++count); if(!PostThreadMessage(nThreadID,MY_MSG,(WPARAM)pInfo,0))//post thread msg { printf("post message failed,errno:%d\n",::GetLastError()); delete[] pInfo; } ::Sleep(1000); } CloseHandle(hThread); return 0; } |
