[Bug python/14382] gdb hangs after plotting with matplotlib

["dje at google dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=14382

dje at google dot com changed:

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                 CC|                            |dje at google dot com

--- Comment #22 from dje at google dot com ---
(In reply to Pedro Alves from comment #21)
> Hmm, I guess I'm confused on how blocking the signal on a thread can help. 
> AFAICS, the main issue is with libraries changing the SIGCHLD sigaction,
> which is process-wide, not per-thread.  So if something sets SA_NOCLDSTOP or
> SIG_IGN on SIGCHLD, that applies to the whole process.
> 
> I just confirmed now that with SIGCHLD set to SA_NOCLDSTOP or SIG_IGN,
> nothing comes out of the signalfd either.
> 
> So the workarounds seem to me to be:
> 
>  - move ptrace handling to a separate process (either always using
> gdbserver, 
>    or a thinner ptrace wrapper/helper)
> 
>  - or perhaps, an evil hack that reimplements sigaction+signal and 
>    ignores requests to ignore SIGCHLD.  References to those functions in   
>    libraries would resolve to gdb's versions, assuming gdb is not itself 
>    a library...

That this won't help with libraries changing SIGCHLD was left as a given, duh.

It was just offered for reference sake.

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