class Subexec

# Subexec

by Peter Kieltyka
github/nulayer/subexec

## Description

Subexec is a simple library that spawns an external command with an optional timeout parameter. It relies on Ruby 1.9's Process.spawn method. Also, it works with synchronous and asynchronous code.

Useful for libraries that are Ruby wrappers for CLI's. For example, resizing images with ImageMagick's mogrify command sometimes stalls and never returns control back to the original process. Subexec executes mogrify and preempts if it gets lost.

## Usage

# Print hello sub = Subexec.run “echo 'hello' && sleep 3”, :timeout => 5 puts sub.output # returns: hello puts sub.exitstatus # returns: 0

# Timeout process after a second sub = Subexec.run “echo 'hello' && sleep 3”, :timeout => 1 puts sub.output # returns: puts sub.exitstatus # returns:

Constants

VERSION

Attributes

command[RW]

exitstatus[RW]

lang[RW]

log_file[RW]

output[RW]

pid[RW]

timeout[RW]

Public Class Methods

new(command, options={}) click to toggle source

# File lib/subexec.rb, line 45
def initialize(command, options={})
  self.command    = command
  self.lang       = options[:lang]      || "C"
  self.timeout    = options[:timeout]   || -1     # default is to never timeout
  self.log_file   = options[:log_file]
  self.exitstatus = 0
end

run(command, options={}) click to toggle source

# File lib/subexec.rb, line 39
def self.run(command, options={})
  sub = new(command, options)
  sub.run!
  sub
end

Public Instance Methods

run!() click to toggle source

# File lib/subexec.rb, line 53
def run!
  if RUBY_VERSION >= '1.9' && RUBY_ENGINE != 'jruby'
    spawn
  else
    exec
  end
end

Private Instance Methods

exec() click to toggle source

# File lib/subexec.rb, line 116
def exec
  if !(RUBY_PLATFORM =~ /win32|mswin|mingw/).nil?
    self.output = `set LANG=#{lang} && #{command} 2>&1`
  else
    self.output = `LANG=#{lang} && export LANG && #{command} 2>&1`
  end
  self.exitstatus = $?.exitstatus
end

spawn() click to toggle source

# File lib/subexec.rb, line 64
def spawn
  # TODO: weak implementation for log_file support.
  # Ideally, the data would be piped through to both descriptors
  r, w = IO.pipe

  log_to_file = !log_file.nil?
  log_opts = log_to_file ? {[:out, :err] => [log_file, 'a']} : {STDERR=>w, STDOUT=>w}
  self.pid = Process.spawn({'LANG' => self.lang}, command, log_opts)
  w.close

  @timer = Time.now + timeout
  timed_out = false

  self.output = ''

  append_to_output = Proc.new do
    self.output << r.readlines.join('')  unless log_to_file
  end

  loop do
    ret = begin
      Process.waitpid(pid, Process::WUNTRACED|Process::WNOHANG)
    rescue Errno::ECHILD
      break
    end

    break if ret == pid

    append_to_output.call

    if timeout > 0 && Time.now > @timer
      timed_out = true
      break
    end

    sleep 0.01
  end

  if timed_out
    # The subprocess timed out -- kill it
    Process.kill(9, pid) rescue Errno::ESRCH
    self.exitstatus = nil
  else
    # The subprocess exited on its own
    self.exitstatus = $?.exitstatus
    append_to_output.call
  end
  r.close

  self
end