CODEWITHSUNDEEP
clinuxmultithreadingpthreads
Giuseppe Pes
Giuseppe Pes

Reputation: 7912

Group together two or more threads

I have a multi-thread application where each thread has a helper thread that helps the first one to accomplish a task. I would like that when a thread is terminated (likely calling exit) the helper thread is terminated as well.

I know that there is the possibility to use exit_group, but this system call kills all threads in the same group of the calling thread. For example, if my application has 10 threads (and therefore 10 additional helper threads) I would like that only the thread and the helper thread associated is terminated, while the other threads keep on running.

My application works exclusively on Linux.

How can I have this behavior?

Reading around about multithreading I got a bit confused about the concept of thread group and process group in Linux. Are these terms referring to the same thing? Precisely, the process group (and perhaps the thread group) is the pid retrieved by one of the following calls :

   pid_t getpgid(pid_t pid);
   pid_t getpgrp(void);                 /* POSIX.1 version */
   pid_t getpgrp(pid_t pid);            /* BSD version */

Upvotes: 1

Views: 441

Answers (1)

Duck
Duck

Reputation: 27542

You are a bit adrift here. Forget exit_group, which these days is the same as exit on linux is not what you are looking for. Similarly the various get-pid calls aren't really what you want either.

The simplest (and usually best) way to handle this is have each primary thread signal its helper thread to shut down and then pthread_join it - or not if it is detached.

So something like:

(a) primary work thread knows - however it knows - its work is done.

(b) signals helper thread via a shared switch or similar mechanism

(c) helper thread periodically checks flag, cleans up and calls pthread_exit

(d) primary worker thread calls pthread_join (or not) on dead helper thread

(e) primary worker cleans up and calls pthread_exit on itself.

There are a lot of variations on that but that's the basic idea. Beyond that you get into things like pthread_cancel and areas you may want to avoid if you don't absolutely require them (and the potential headaches).

Upvotes: 1

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