Rails Ruby on Rails → 3.x

The following code should print one line and exit. Instead, it runs forever.

#!/usr/bin/ruby

require 'active_record'

ActiveRecord::Base.establish_connection(
    :adapter  => "mysql",
    :database => "your-db",
    :username => "your-user",
    :password => "your-password",
    :host     => "your-server"
    )

ActiveRecord::Base.connection # connect to the server

# Uncomment the following line to work around bug.
# Rather than using SIG_IGN, set a do-nothing signal handler.
# SIG_IGN is inherited by children (e.g. via system),
# which we don't necessarily want.
# The a specific handler like this will cause children to use SIG_DFL.
# Signal.trap("SIGPIPE") {}

# The following "od" command will print random bits forever,
# but it should be stopped by SIGPIPE from head after just one line.
# Unfortunately ActiveRecord will set SIGPIPE to SIG_DFL,
# causing od not to receive SIGPIPE and therefore to run forever.
system("od /dev/urandom | head -1") # should print one line and return

If your system doesn't have "od" or "/dev/urandom" you can instead use the following trivial C program (which if run by itself will terminate immediately):

#include <signal.h>

int main()
{
    for(;;)
        raise(SIGPIPE);
    return 0;
}

Then replace the string passed to "system" with the path to your compiled C program.

You can make the script work correctly by either commenting out the call to "connection" (or completely removing the ActiveRecord code), or by uncommenting the call to Signal.trap. This latter workaround is probably what ActiveRecord should be doing on its own: setting a do-nothing signal handler for SIGPIPE, rather than using SIG_IGN. This is because SIG_IGN is inherited by the child process in "system", which causes surprising behavior, whereas any custom signal handler is reset to SIG_DFL upon exec.

Running the program under "strace -f" (on Linux; try "truss" on Solaris) shows the culprit call:

sigaction(SIGPIPE, {SIG_IGN}, {0x..., [], SA_RESTORER, 0x...}, 8)

Edited by Rohit Arondekar for formating.