title: How to send message (in C) from one thread to another?
body: <p>I'm trying to send a message from one thread to another. Each thread knows the thread ID of the other. How can I send a message between them?</p>
  
  <p>I've already seen some proposed solutions (message queue, anonymous pipe, etc.) but honestly I didn't get them to work. Obviously I didn't understand the previous descriptions enough, hence this topic.</p>
  
  <p>So to sum up, just the shortest possible way to send, let's say a message "Hello!" from thread to another thread, make the 2nd thread show it on stderr, and than send back to 1st thread message 'Hello back!'.</p>
  
  <p>It's probably very easy and I didn't do a good job of researching, but I've been stuck for some time now, and can't find decent way to do this.</p>