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 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 msg
sprintf(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