[adrusi]

The surprising behavior was that the child process received the configured signal not when the process that created it exited, but rather when the specific thread that called fork(2) exited.

The parent process was an event loop based python program whose main function was to manage the creation and deletion of these child processes, and the simplest way to spawn child processes without blocking the event loop is to call fork(2) on a thread pool. My thread pool was triaging the number of worker threads based on demand, so occasionally it would decide a worker was no longer needed, and all the child processes that happened to have been created on that thread would get SIGKILL'd — something you rarely want when using a thread pool!

I didn't want the child processes to die unless the parent process's business logic decided they were no longer needed, or if the parent was itself killed (this latter reason being the motivation for setting PDEATHSIG).

Once I understood why my processes were dying, the solution was simple: make sure the worker threads never exit.

[gwright]

Well that certainly seems unexpected.

[ykonstant]

Jesus Christ.