把window线程间传送消息仔细的看了一遍，觉得以前的理解很不深刻。说一说对PostThreadMessage的理解。
PostThreadMessage是一个线程体发送一个消息到指定的线程ID，其原型如下：
BOOL PostThreadMessage(DWORD idThread,UINT Msg,WPARAM wParam,LPARAM lParam);这个函数既可以发送消息给工作线程，也可以发送给UI线程。接受PostThreadMessage的线程必须已经有了一个message queue，否则调用PostThreadMessage会失败。因为此原因使用GetLastError会得到错误码为1444，这种情况经常出现，解决方法有如下两种：
1. 调用PostThreadMessage，如果失败，就Sleep一段时间再次调用PostThreadMessage直到调用成功；
2. 创建一个Event对象，让PostThreadMessage等待接受的线程创建一个message queue。可以通过调用PeekMessage强制系统创建一个message queue。示例代码如下：
假设mainAPP是发送线程ThreadA是接受线程
/*mainAPP.cpp*/……hStartEvent = ::CreateEvent(0,FALSE,FALSE,0); //create thread start eventif(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是接受线程
/* 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传递的消息如果要包含信息，要注意在结束的时候释放消息中的信息。在消息中附加信息方法如下
/*构造信息如下*/char* pInfo = new char[MAX_INFO_SIZE]; //create dynamic msgsprintf(pInfo,"msg_%d",++count);PostThreadMessage(nThreadID,MY_MSG,(WPARAM)pInfo,0)//post thread msg/*解释信息如下*/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; //这里释放了资源break;}}做了一个简单的消息通信实验，让主线程中等待用户输入，产生不同的消息，并把这些消息post给子线程，子线程根据产生的消息做出不同的反映。这些子线程可以是工作线程也可以是UI线程。
#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; } |
要把SETTING 改为多线程的
Project->Settings->click C/C tab,
在Category 中选Code Generation, 然后在Use run-time libray 中选一个
Multithread 配置
