From: Tim Uckun <timuckun@...>
Date: 2010-09-22T21:31:35+09:00
Subject: having problems with open4 and stuck forked processes

I am running a batch process which uses the wkhtmltoimage-i386 binary
to make screenshots of urls.  Unfortunately this is in beta and it
frequently hangs up and takes up 100% of one of the CPUs on the
machine.

I have the following code to try and detect the hung process and kill
it but it doesn't always work and I was wondering if anybody has a
better idea of how to do this.  When I run it by testing simple
commands like sleep it works perfectly. In production with this binary
it doesn't seem to always work.

def Util.shell_with_timeout(cmd, seconds = 3600)
    #the default timeout is an hour. That's probably way too long

    Timeout::timeout(seconds) {
      @pid, @stdin, @stdout, @stderr = Open4.popen4(cmd)
      ignored, @status = Process::waitpid2 @pid
      if @status.exitstatus != 0
        raise "Exit Status not zero"
      end
    }

    @stdout ? @stdout.read.strip : ''
  rescue Timeout::Error
    Process.detach @pid
    Process.kill 'SIGKILL', @pid
    raise "Process Timed out"
  rescue => e
    msg =  @stderr ?  @stderr.read.strip : ''
    msg +=   e.to_s
    raise "Error during execution of command #{cmd}\n #{msg}"
  end