Re: why "in_sighandler"?

[Jan Djärv]

YAMAMOTO Mitsuharu skrev:
> > > > > > 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?

What exactly do you mean by interrupted?  In the sense that they don't get to 
execute, yes they are interrupted.  When a signal handler is running, no 
threads can run (on a single CPU machine), hence they are all interrupted.


> 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.

That can't be it.  The mutex is recursive, so a thread is able to take it 
multiple times.

        Jan D.