Signal handling tune up.

Pierre A. Humblet
Sun Aug 31 20:13:00 GMT 2003

At 02:39 PM 8/31/2003 -0400, you wrote:
>On Sun, Aug 31, 2003 at 11:23:52AM -0400, Pierre A. Humblet wrote:
>>thanks for your quick response to the ftp crash.
>It would have been much quicker if I'd clued into the fact that an
>address like a0dc018 != a0dc01c.  It took my 127 attempts at running ftp
>to finally see what was going on.
>I can't believe that this hasn't caused problems for other programs.
>It's a pretty serious problem.  Every time I think I've got this fixed
>another corner case occurs to me which has to be dealt with.

I had the feeling I had seen mails on gethostbyname before.
So I suspected it wasn't trivial and I spent the evening on 
other kind of activities !

>>writev (const int fd, const struct iovec *const iov, const int iovcnt)
>>  sig_dispatch_pending ();
>>  sigframe thisframe (mainthread);
>>The call to sig_dispatch_pending is meant for the case where
>>there is a pending signal. Assume there indeed is one.
>>The call to sig_dispatch_pending will setup an interrupt in sigsave. 
>>The return address on the stack will be the first interruptible return 
>>address above sig_dispatch_pending, i.e. the return address of writev.
>>The handler will not be entered until writev returns.
>Ok.  I see what you mean but the old code was not actually right either.
>I wrote a test case (enclosed) which sent a signal to a process running
>a modified version of cygwin1.dll after the call to sigframe
>("guaranteed" with the judicious use of Sleep) in sig_dispatch_pending.
>The 'ouch' wasn't triggered by the either the old or new cygwin code.
>So, I've checked in new code in sig_dispatch_pending.

Why would the ouch be triggered? The parent is long dead when
the child kills its ppid, which by that time is 1.

                                nanosleep: 0 = nanosleep (200, 0)
  428 1593118 [main] a 75308827 kill: kill (1, 1)   <=== dad is gone
  413 1593531 [main] a 75308827 sig_dispatch_pending: pending_signals 0
 1088 1594619 [main] a 75308827 sig_dispatch_pending: no need to wake
anything up
  576 1595195 [main] a 75308827 __set_errno: int kill_worker(int, int):181
val 3


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