Question

I have two processes which access to the same physical memory(GPIO data addr).
So how can I have synchronized between these apps?
I understand that we have some kind of locking mechanism such as mutex and semaphore, so which method is the fastest?

Thank for your help,

-nm

Answer 1

Mutexes and semaphores are generally considered to be concurrency solutions in the same address space — meaning that different parts of the same program will lock their access to a resource using one of these contraptions.

When you’re dealing with separate processes, the standard way to do this on Linux is to create something in /var/lock, like /var/lock/myapp.lock, and place your PID followed by a newline in it. Then other processes will check for its existence, and if you’re crafty check the PID to make sure it’s still alive, too.

If you need real-time access to the area, skip the filesystem and the processes will have to communicate via IPC (LET_ME_KNOW_WHEN_DONE, OKAY_IM_DONE, you get the idea), or — better — write a process whose sole purpose is to read and write to the GPIO memory, and your other programs communicate with it via IPC (probably the best approach).