Message passing tutorial

I’ve got two programs, one which does background processing , and one which handles the display of data created by the background processing, in this case a PhImage_t created in a memory context thingy (thanks cdm). I’m trying to set up a message passing setup so that the background process can say ‘that PhImage_t you wanted is done’, and then the display process can say ‘ok, I’m finished with it now’ so the background process can resume messing with the PhImage_t. The PhImage_t is in shared memory and that works fine.

I used to have this in threads in the same process, and it worked well except that I had to do PtEnter() and PtLeave() in the processing thread, or it would segfault, and this meant it slowed down the display thread too much.

So, any pointers to message passing tutorials, or tips on some other way of controlling the above will be much appreciated.