ruby timeouts and system commands

Question

I have a ruby timeout that calls a system (bash) command like this..

Timeout::timeout(10) {
  `my_bash_command -c12 -o text.txt`
}

but I think that even if the ruby thread is interrupted, the actual command keeps running in the background.. is it normal? How can I kill it?

Answer 1

I think you have to kill it manually:

require 'timeout'

puts 'starting process'
pid = Process.spawn('sleep 20')
begin
  Timeout.timeout(5) do
    puts 'waiting for the process to end'
    Process.wait(pid)
    puts 'process finished in time'
  end
rescue Timeout::Error
  puts 'process not finished in time, killing it'
  Process.kill('TERM', pid)
end

Answer 2

in order to properly stop spawned process tree (not just the parent process) one should consider something like this:

def exec_with_timeout(cmd, timeout)
  pid = Process.spawn(cmd, {[:err,:out] => :close, :pgroup => true})
  begin
    Timeout.timeout(timeout) do
      Process.waitpid(pid, 0)
      $?.exitstatus == 0
    end
  rescue Timeout::Error
    Process.kill(15, -Process.getpgid(pid))
    false
  end
end

this also allows you to track process status

Answer 3

Perhaps this will help someone else looking to achieve similar timeout functionality, but needs to collect the output from the shell command.

I've adapted @shurikk's method to work with Ruby 2.0 and some code from Fork child process with timeout and capture output to collect the output.

def exec_with_timeout(cmd, timeout)
  begin
    # stdout, stderr pipes
    rout, wout = IO.pipe
    rerr, werr = IO.pipe
    stdout, stderr = nil

    pid = Process.spawn(cmd, pgroup: true, :out => wout, :err => werr)

    Timeout.timeout(timeout) do
      Process.waitpid(pid)

      # close write ends so we can read from them
      wout.close
      werr.close

      stdout = rout.readlines.join
      stderr = rerr.readlines.join
    end

  rescue Timeout::Error
    Process.kill(-9, pid)
    Process.detach(pid)
  ensure
    wout.close unless wout.closed?
    werr.close unless werr.closed?
    # dispose the read ends of the pipes
    rout.close
    rerr.close
  end
  stdout
 end

Answer 4

Handling processes, signals and timers is not very easy. That's why you might consider delegating this task: Use the command timeout on new versions of Linux:

timeout --kill-after 5s 10s my_bash_command -c12 -o text.txt