Sending signals to a subprocess

Christopher Faylor
Wed Oct 20 21:10:00 GMT 2010

On Wed, Oct 20, 2010 at 08:25:37PM +0100, Andy Koppe wrote:
>On 20 October 2010 13:20, Andy Koppe wrote:
>>>Corinna made tcgetpgrp return 0 instead of -1 in some circumstances
>>>because she saw Linux doing that.  ??But when I run Corinna's test on
>>>my Linux system, I get -1 where she got 0.  ??So not all Linuxes agree
>>>on what tcgetpgrp should do.
>>Hmm, Corinna's test calls tcgetpgrp(master) in the parent only before
>>the child is forked and after it exited, so it's correct to report that
>>there's no foreground process.
>>I wonder which Linux it was that returned 0 in case of failure.  I've
>>tried it on a recent Opensuse, an old Redhat with a 2.6.9 kernel, and
>>also a Debian with a 2.4 kernel, and got -1 on all of those.
>Actually I'd only tried my test on all three systems, whereas I'd tried
>Corinna's only on the old Redhat, where it did print -1 for failure.
>On the 2.4 system it can't open /dev/ptmx, whereas on the Opensuse with
>2.6.34 I do get the results Corinna reported, including 0 on the master
>side of the pty when enquiring from the parent.  (Process 0 is the
>startup process, so I guess that makes some sense.)
>To bring my ramblings to some sort of conclusion, here's a slightly
>amended version of Corinna's test that checks the master side from the
>parent process before, *during* and after the child process:

FYI, I'm sticking with the test case that I first posted several days
ago and which has been cruelly ignored ever since.  I've been slowly
modifying it for the last several days.

I think I'm seeing some pattern to the way Linux handles this and I should
be able to make Cygwin work the same way.

Just in case it isn't clear, this all has nothing, AFAICT, to do with the
fact that Cygwin doesn't implement TIO[CS]PGRP but I have implemented those
two ioctl's nonetheless.


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