使用PostThreadMessage向工作线程发送消息

参考文章：http://blog.csdn.net/liuliu20036/article/details/3879152 http://blog.chinaunix.net/uid-20596472-id-1918307.html
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 "stdafx.h"
#include <Windows.h>
#include <process.h>
#include <cstdio>

#define MY_MSG WM_USER + 100
const int MAX_INFO_SIZE = 20;

HANDLE g_hEvent;
HANDLE m_hThread;
unsigned int m_nThreadId;

unsigned _stdcall ThreadFunc(LPVOID lpParam)
{
printf("thread fun start/n");
MSG msg;
PeekMessage(&msg,NULL,WM_USER,WM_USER,PM_NOREMOVE);

if(!SetEvent(g_hEvent)) //set thread start event
{
printf("Set Event fail: %d",GetLastError());
return 0;
}

while(true)
{
if(GetMessage(&msg,NULL,0,0))//get msg from message queue
{
switch (msg.message)
{
case MY_MSG:
char* pInfo = (char*)msg.wParam;
printf("recv %s",pInfo);
printf("\n");

delete [] pInfo;
break;

}
}
}

return 0;
}

int _tmain(int argc, _TCHAR* argv[])
{
g_hEvent = CreateEvent(NULL,FALSE,FALSE,NULL);//create thread start event
if(g_hEvent == NULL)
{
printf("Create Event Fail: %d",GetLastError());
return 0;
}

//start thread
m_hThread =(HANDLE)_beginthreadex(NULL,0,ThreadFunc,NULL,0,&m_nThreadId);
if(m_hThread == NULL)
{
printf("Create New Thread fail :%d",GetLastError());
return 0;
}

//wait thread start event to avoid PostThreadMessage return errno:1444
WaitForSingleObject(g_hEvent,INFINITE);
CloseHandle(g_hEvent);

int count = 0;
while(true)
{
char* pInfo = new char[MAX_INFO_SIZE];//create dynamic msg
sprintf(pInfo,"msg_%d",++count);

if(!PostThreadMessage(m_nThreadId,MY_MSG,(WPARAM)pInfo,0))//post thread msg
{
p
4000
rintf("post message failed,errno: %d/n",GetLastError());
delete [] pInfo;
}

if(count >= 20)
{
break;
}

Sleep(1000);
}

CloseHandle(m_hThread);

getchar();
return 0;
}