Re: why "in_sighandler"?

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Tue, 22 Aug 2006 08:38:54 +0200, Jan Djärv <jan.h.d@swipnet.se> 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
				mituharu@math.s.chiba-u.ac.jp