windows平台发消息到非UI线程.

下面的代码是介绍如何在windows平台发消息到非UI线程. 
主要是'PeekMessage || GetMessage' 这两个API的应用. 当他们被调用的时候，如果当前线程还没有消息循环，就会创建一个.
利用这个特性比自己手动的去创建一个消息循环要方便得多. 
发消息主要是使用线程PostThreadMessage

#include <iostream>
#include <string>
#include "cassert"
#include "windows.h"
#include "process.h"

enum { MSG_TEST = WM_USER+100,MSG_EXIT };

unsigned __stdcall fun(void *param)
{
    MSG msg;

    while(true)
    {
        if(GetMessage(&msg,0,0,0)) //get msg from message queue
        {
            char * info = reinterpret_cast<char*>(msg.wParam);
            bool keep_in_loop = true;
            switch(msg.message)
            {
            case MSG_TEST:
                std::cout << info << std::endl;
                break;
            case MSG_EXIT:keep_in_loop=false;
                std::cout << info << std::endl;
                break;
            default: break;
            }


            if ( ! keep_in_loop )
            {
                break;
            }
        }
    }
    std::cout << "out of loop" << std::endl;
    return 0;
}


void main()
{
    HANDLE hThread;
    unsigned nThreadID;

    //start thread
    hThread = (HANDLE)_beginthreadex( NULL, 0, &fun, NULL, 0, &nThreadID );

    while(true)
    {
        UINT Msg = MSG_TEST;
        const char * p = "MSG_TEST";

        std::string commond;
        std::cin >> commond;
        if ( commond == "exit" )
        {
            Msg = MSG_EXIT;
        }

        BOOL bPostOK = PostThreadMessage(nThreadID,Msg,(WPARAM)p,0);
        if ( ! bPostOK )
        {
            assert( false );
            // the post event is to too early, please build msg loop first
            // 'PeekMessage || GetMessage' will forced to build the msg loop, if it does not exist.
        }
    }
}