[Q] what to do when waitpid() returns ECHILD under signal(SIGCHLD, SIG_IGN)?

From: Junio C Hamano <junkio@cox.net>
Date: Jun 19, 2006, 23:49 UTC
Message-ID: <7vwtbc7ll6.fsf@assigned-by-dhcp.cox.net>

Somebody I met last week in Japan reported that the socks client he uses to cross the firewall to connect to git:// port from his company environment seems to do signal(SIGCHLD, SIG_IGN) before spawning git. When "git clone" is invoked this way, we get a mysterious failure.

I can reproduce the problem without using funny socks client like this:

        : gitster; trap '' SIGCHLD
        : gitster; git clone git://git.kernel.org/pub/scm/git/git.git/ foo.git
        error: waitpid failed (No child processes)
        fetch-pack from 'git://git.kernel.org/pub/scm/git/git.git/' failed.
        : gitster; ls foo.git
        ls: foo.git: No such file or directory

We could work this around by having signal(SIGCHLD, SIG_DFL) upfront in git.c::main(), but I am wondering what the standard practice for programs that use waitpid() call. Do they protect themselves from this in order to reliably obtain child exit status? Or do they simply consider it is a user error to run a program that use waitpid() with SIGCHLD ignored?

http://www.opengroup.org/onlinepubs/009695399/functions/waitpid.html

explicitly says this is an expected behaviour, so barfing upon ECHILD sounds like a bug on our part.