I have process which forks a lot. Child processes do lot of stuff and another system calls.
When ANY child process gets error from system call, it prints error description to stderr and send SIGUSR1 to group leader (main parent process).
SIGUSR1 tells parent to kill all child processes, free resources and exit program execution (to avoid zombie processes).
I need to kill all children at once. Atomically. So when any error happens in ANY child process, all child processes stops with their work immediately.
Currently parent process kills all child processes with SIGUSR2 - It sends this signal to all process group members (killpg) - all of them have signal handler installed which kills them (exit) - group leader won't get killed though (it still needs to free resources).
The problem is that before all child processes get killed, they still can execute about 1-2 rows of code, which is not what I want. I need to stop them immediately.
How can I achieve this?
Signals are delivered in a async fashion, since both parent and child processes are running, you cannot expect the child process will handle the signal immediately when parent send the signal.
The problem is that before all child processes get killed, they still can execute about 1-2 rows of code, which is not what I want. I need to stop them immediately.
Your problem is more of a coordination and synchronization between processes, rather than signal handles. There are two ways I can think of:
Use synchronized signals. That is when each child send SIGUSR1 to the parent, they stop working, and wait on SIGUSR2 signal by the waiting functions, like sigtimedwait, or sigwait, in this way, they will not run any additional code before exiting.
Use pipe or socketpair to create communication channels between parent and children, that is, parent send kill instruction to children, and each child will free necessary resources and kill themselves. This requires children to listen on the channel while doing work.