Date:	Sun, 2 Jan 2000 11:23:36 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender:	eliz AT is
To:	Steve Ball <steve AT effectivejava DOT com>
cc:	djgpp AT delorie DOT com
Subject:	Re: system() hangs or returns incorrect value when child process killed
In-Reply-To:	<84m1ad$pbis$1@titan.xtra.co.nz>
Message-ID:	<Pine.SUN.3.91.1000102112005.1710e-100000@is>
MIME-Version:	1.0
Reply-To:	djgpp AT delorie DOT com
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On Sun, 2 Jan 2000, Steve Ball wrote:

> Does anyone know a workaround for this bug?

I didn't see any bugs in what you describe.  It's all expected
behavior.

> If the child process is killed using ^C or ^-Break, system() should return a
> value with SIGINT in bits 8-17.

Ideally, yes; but it doesn't always work.  DOS is very inconsistent in
this aspect, especially since many programs catch ^C and ^BREAK and do
custom things before they exit.

> 1. If the child process is a .COM file (such as CHOICE.COM), the return
> value is zero.

It depends on what the .COM program return when aborted.

> 2. More importantly, if it is a DJGPP-compiled program, the return value is
>    255 (as if the process had terminated by calling exit(255)).

This is expected behavior for a DJGPP program, assuming that it does
not install a handler for the signal SIGINT.  If it does install a
SIGINT handler, the result depends on what the handler returns (if it
exits to DOS).

> 3. If the command line is "DELTREE \SOMEDIR", killing the child process with
>    ^C hangs the DOS session (this works okay if entered from the shell).

I don't think it hangs, I think it waits for the keyboard input.  Try
typing "n [Enter]" at that point, and see if the program continues to
run.

In general, aborting a program that reads the keyboard sometimes
requires you to type some input before the program aborts, because
aborting the program from within a DOS call (the one which reads the
keyboard) is not always possible.

> errno is not set in any of these cases

`system' is only documented to set `errno' if it cannot run the child
program.  Aborting the child program is not documented, and is not
supposed, to set `errno'.

> I have posted this buf to the DJGPP bug list
> (http://www.delorie.com/djgpp/bugs/show.cgi?000311) but, right now, I'm keen
> to find a workaround...

Please do not submit bug reports to the bug-tracker unless you are
absolutely positive that you have found a bug in DJGPP.  In
particular, we cannot possibly repair any lossage that is caused
by the OS or by non-DJGPP programs running on that OS.

Please always post a bug report here before submitting it to the bug 
tracker.  I spend a lot of time closing bug reports which aren't bugs
at all, or aren't DJGPP bugs.

> How can I tell if a child process was terminated (so the parent can
> terminate too)?

Please post more details about what you are trying to accomplish.  It
is hard to give intelligent advice without knowing the details.

In general, pressing ^C while the child program runs delivers the
signal SIGINT to its parent(s) as well, so the parent doesn't need to
do anything to terminate: it will be aborted automatically once the
child exits.

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