A question on sigchld_handler

A question on sigchld_handler

[Herbert Euler]

Hello,

Here is a question on the SIGCHLD handler, `sigchld_handler' in
process.c.

Could SIGCHLD possibly be delivered more than once to Emacs, so that
`sigchld_handler' is invoked more than once?  For example, SIGCHLD
arrives first, hence `sigchld_handler' gets called.  Before it
finishes, SIGINT arrives, so `sigchld_handler' is suspended and
`interrupt_signal' gets called.  Before `interrupt_signal' finishes,
another SIGCHLD arrives and so `sigchld_handler' gets called again.
Is that possible?

Regards,
Guanpeng Xu
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Re: A question on sigchld_handler

[Andreas Schwab]

Herbert Euler <herberteuler@hotmail.com> writes:

> Could SIGCHLD possibly be delivered more than once to Emacs, so that
> `sigchld_handler' is invoked more than once?

A signal is blocked as long as its handler hasn't returned.  Thus that
can only happen when the signal is explicitly unblocked, or the function
is called manually.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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RE: A question on sigchld_handler

[Herbert Euler]

>> Could SIGCHLD possibly be delivered more than once to Emacs, so that
>> `sigchld_handler' is invoked more than once?
>
> A signal is blocked as long as its handler hasn't returned. Thus that
> can only happen when the signal is explicitly unblocked, or the function
> is called manually.

Thank you very much!  :D

So I misunderstood the GNU Libc manual.

There are Lisp_Objects used in `sigio_handler', and other structs used
in other signal handlers.  These data structures seem not atomic to
signals.  How are non-atomic problems avoided here?

Regards,
Guanpeng Xu
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