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Re: busyloop in sigchld_handler

From: Andreas Schwab
Subject: Re: busyloop in sigchld_handler
Date: Mon, 12 Mar 2007 19:45:03 +0100
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/22.0.91 (gnu/linux)

Sam Steingold <address@hidden> writes:

> Andreas Schwab wrote:
>> Sam Steingold <address@hidden> writes:
>>> wait3 is a system call, which, when invoked in a loop, prevents the
>>> kernel from doing anything else (in this case, sending SIGCHLD to
>>> emacs). sleep allows the kernel some time to pass the signal.
>> I don't find this explanation convincing at all.  Since the system call is
>> made _inside_ the signal handler, the signal is actually blocked here, so
>> it cannot be delivered anyway.
> yes, you are right.
> what I should have said was that by making a system call in a busyloop,
> emacs prevents the kernel from doing what it needs to do to the the child
> so that wait3 will succeed.

What does the kernel have to do?  The EINTR error will only happen when
the system call was interrupted _and_ a signal handler was called.


Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

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