Re: 'stop-server-and-clients!' can cause crash (was PATCH - Add cooperative REPL server module)

[Mark H Weaver <mhw@netris.org>]

David Thompson <dthompson2@worcester.edu> writes:

> Mark H Weaver <mhw@netris.org> writes:
>
>> Interesting.  Does it happen with unmodified stable-2.0?  If so, I think
>> we can treat this as an independent bug.
>
> Yes, exact same problem on stable-2.0.
>
>> Can you reproduce the segfault while running meta/gdb-uninstalled-guile
>> and get a backtrace?  Alternatively, if you provide enough detail to
>> reproduce the segfault, I can track it down.
>
> Here's the output from gdb:
>
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7ffff4ea2700 (LWP 13122)]
> get_codepoint (port=port@entry=0xe13ff0, codepoint=codepoint@entry=0x7ffff4ea1334, buf=buf@entry=0x7ffff4ea1330 "(%`", 
>     len=len@entry=0x7ffff4ea1338) at ports.c:1460
> 1460	      update_port_lf (*codepoint, port);

Ah yes, this makes sense.  Ports in stable-2.0 are not thread-safe even
for normal operations, and in this case 'stop-server-and-clients!' is
_closing_ a port that's currently in use by another thread.

In other words, 'stop-server-and-clients!' is fundamentally unsafe in
the way it works, and probably has been since it was introduced.

Thanks for the debugging.  I'll think about how best to fix this.

     Mark