使用PostThreadMessage向工作线程发送消息

参考文章：http://blog.youkuaiyun.com/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
		{
			printf("post message failed,errno: %d/n",GetLastError());
			delete [] pInfo;
		}

		if(count >= 20)
		{
			break;
		}

		Sleep(1000);
	}

	CloseHandle(m_hThread);

	getchar();
	return 0;
}