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Re: Sending signals to a subprocess

On 10/20/2010 4:32 PM, Christopher Faylor wrote:
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.

This seems to be fixed in the latest snapshot, as far as emacs is concerned. I no longer see any difference between Cygwin and Linux there. I also get the expected results when I run the test cases that Andy posted. But when I run the original test case that you posted in

I'm getting strange behavior. I ran it with no argument, getting

0 = tcgetpgrp(4)
0 = ioctl(fd, TIOCGPGRP, &pid), pid = 0

but then the terminal seemed to hang, and I didn't get a new prompt. I tried this both in mintty and xterm.


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