Use postthreadmessage to send messages to the working thread

I read the messages sent between the window threads carefully and felt that the previous understanding was not profound. Let's talk about postthreadmessage.

Postthreadmessage is a thread body that sends a message to the specified Thread ID. Its prototype is as follows: bool postthreadmessage (DWORD idthread, uint MSG, wparam, lparam ); this function can send messages to the worker thread or the UI thread. The thread that accepts postthreadmessage must already have a message queue; otherwise, calling postthreadmessage will fail. If getlasterror is used for this reason, the error code 1444 is returned. In this case, there are two solutions:

1. Call postthreadmessage. If the call fails, sleep will call postthreadmessage again for a period of time until the call is successful;

2. Create an event object so that a message queue can be created for a thread whose postthreadmessage is waiting for acceptance. You can call peekmessage to force the system to create a message queue. ExampleCodeAs follows:

Assume that mainapp is the sending thread and threada is the receiving thread/* 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 is the acceptance thread/* threada */

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 )){

Switch (msg. Message ){

Case wm_message_a:

......

Break;

}}}}

// If the message passed by postthreadmessage needs to contain information, you must release the information in the message at the end. The method for attaching information to a message is as follows/* The construction information is as follows */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

/* The explanation is as follows */

If (getmessage (& MSG, 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; // The resource Break is released here;

}}

 

A simple message communication experiment was conducted to let the main thread wait for user input, generate different messages, and post these messages to the sub-thread, the subthread generates different responses based on the messages generated. These subthreads can be working threads or UI threads.

# Include

# Include

# Include

# 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;

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) // 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;

}