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Re: why "in_sighandler"?

From: YAMAMOTO Mitsuharu
Subject: Re: why "in_sighandler"?
Date: Tue, 22 Aug 2006 16:39:53 +0900
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>>>>> On Tue, 22 Aug 2006 08:38:54 +0200, Jan Djärv <address@hidden> said:

> How can it be otherwise?  If you only have one program counter, that
> program counter must be changed to the signal handler no matter how
> many threads you have, i.e. any previous execution (regardless of
> thread) is interrupted.

Not-running threads have already been *interrupted* by context
switching.  Are they interrupted by a signal again?

> When I say interrupted I mean that the signal handling function
> starts to run.  You obviously mean something else.  But this is a
> side issue, it has more to do with reentrance of the function
> interrupted rather than which thread is currently running.

I don't understand why non-signalled threads are relevant as long as a
signal handler only executes thread-safe functions.  The problem of
async-signal-unsafe function is that a thread that took a lock in the
normal context may try to take the same lock in a signal handler
context.  The thread cannot go back to the normal context where the
lock will be released afterwards, but just waits for the lock in the
signal handler.  As a result, the thread gets stuck.  That's
irrelevant to the other threads.

                                     YAMAMOTO Mitsuharu

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