1.7.0: question about signal delivery to pthreads

Mon Dec 7 15:46:00 GMT 2009

Hi everybody!
I have a question regarding the delivery of signals to pthreads in 
Cygwin (1.7 beta). As an example, please consider the following 
situation (see attached file for source code):
There are two threads, a main thread and another one created by the main 
thread.
The main registers a SIGALRM signal handler (sigaction), creates the 
other thread (pthread_create), blocks all signals (pthread_sigmask), 
then waits for a SIGHUP (sigwait) before joining the other thread 
(pthread_join).
The other thread unblocks all signals (pthread_sigmask), then schedules 
an alarm (alarm(1)) and goes to sleep (sleep(5)).
In this situation, I had expected the other thread to receive the 
SIGALRM, and to wake up from sleep consequently; at least it did in 
Linux (2.6.31). However, in Cygwin the signal never arrives, the thread 
sleeps the full turn.
It seems the signal gets delivered to the blocked main thread instead, 
but attempting to check (sigpending) results in a segmentation fault 
(SEGV) for some reason.
If I explictly remove the SIGALRM from the block mask, the signal 
handler gets called and sigpending works, but of course this interrupts 
sigwait (errno=EINTR), hence this is not a viable workaround for me.
So, is cygwin behaving correctly here (in a POSIX sense), or is this a 
bug? Please help me understand.
Thank you,
Karsten Otto
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