* A question on sigchld_handler
@ 2007-12-27 6:46 Herbert Euler
2007-12-27 9:41 ` Andreas Schwab
0 siblings, 1 reply; 3+ messages in thread
From: Herbert Euler @ 2007-12-27 6:46 UTC (permalink / raw)
To: emacs-devel@gnu.org
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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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: A question on sigchld_handler
2007-12-27 6:46 A question on sigchld_handler Herbert Euler
@ 2007-12-27 9:41 ` Andreas Schwab
2007-12-27 10:10 ` Herbert Euler
0 siblings, 1 reply; 3+ messages in thread
From: Andreas Schwab @ 2007-12-27 9:41 UTC (permalink / raw)
To: Herbert Euler; +Cc: emacs-devel@gnu.org
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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^ permalink raw reply [flat|nested] 3+ messages in thread
* RE: A question on sigchld_handler
2007-12-27 9:41 ` Andreas Schwab
@ 2007-12-27 10:10 ` Herbert Euler
0 siblings, 0 replies; 3+ messages in thread
From: Herbert Euler @ 2007-12-27 10:10 UTC (permalink / raw)
To: Andreas Schwab; +Cc: emacs-devel@gnu.org
>> 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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2007-12-27 6:46 A question on sigchld_handler Herbert Euler
2007-12-27 9:41 ` Andreas Schwab
2007-12-27 10:10 ` Herbert Euler
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