Send message across threads

Today, my colleague asked a question, saying that the process of sending message is the same as that of calling directly, but thread tracking finds that the process is completed in the receiving message queue. When I go home, I can see some arguments in the blog garden. I will post them here to encourage them.

Http://bbs.csdn.net/topics/390715501? Page = 1

If the specified window was created by the calling thread, the window procedure is called immediately as a subroutine. if the specified window was created by a different thread, the system switches to that thread and callthe appropriate window procedure. messages sent between threads are processed only when the processing ing thread executes message retrieval code. the sending thread is blocked until the processing ing thread processes the message.