How to terminate correctly program?

[Christian Helmuth]

Hi Alexander,

On Mon, Jan 06, 2020 at 13:19:15 CET, Alexander Tormasov via users wrote:
> I try to finish a program with a lot of threads (eg 6). In
> particular, it call libc exit(0) from one of them.
> 
> Then seems that it start to free memory , and one of threads
> accidentally receive timer event, and try to access its own memory -
> and fail because it already became inaccessible.
> 
> Unfortunately I do not have normal control over it (this is just a
> behavior of golang “hello world” program!)
> 
> Can I forcible cancel all timers/signals inside program threads and
> stop all activities to avoid such problems? Better without races ;)

Unfortunately, you're stumbling over an unfinished feature of our
current libc runtime - complete support for multithreading. In your
case, I expect the first thread calling exit() just executes all
destructors and atexit handlers, which leaves the component in an
almost terminated state.

If you like to improve this by force-stopping all other threads before
finalizing the component, you could look into the libc implementation
and implement a kind of termination broadcast and signal handler for
this purpose. This mechanism should pthread_join all other threads and
therefore be implemented in the main entrypoint. Sounds complex? It
really is! For example, the FreeBSD libc has support for thread-local
dtors (which is a very good idea because of __thread/_Thread_local/thread_local
in C/C++) that must be executed if a pthread terminates.

Greets
-- 
Christian Helmuth
Genode Labs

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