text: import time, os, sys, logging
  from subprocess import Popen, PIPE, STDOUT
  
  TRACK_PROCESS_SPAWNS = True if (os.getenv('EM_BUILD_VERBOSE') and int(os.getenv('EM_BUILD_VERBOSE')) >= 3) else False
  
  def timeout_run(proc, timeout=None, note='unnamed process', full_output=False):
    start = time.time()
    if timeout is not None:
      while time.time() - start < timeout and proc.poll() is None:
        time.sleep(0.1)
      if proc.poll() is None:
        proc.kill() # XXX bug: killing emscripten.py does not kill it's child process!
        raise Exception("Timed out: " + note)
    out = proc.communicate()
    out = map(lambda o: '' if o is None else o, out)
    if TRACK_PROCESS_SPAWNS:
      logging.info('Process ' + str(proc.pid) + ' finished after ' + str(time.time() - start) + ' seconds. Exit code: ' + str(proc.returncode))
    return '\n'.join(out) if full_output else out[0]
  
  def make_command(filename, engine=None, args=[]):
    if type(engine) is not list:
      engine = [engine]
    # Emscripten supports multiple javascript runtimes.  The default is nodejs but
    # it can also use d8 (the v8 engine shell) or jsc (JavaScript Core aka
    # Safari).  Both d8 and jsc require a '--' to delimit arguments to be passed
    # to the executed script from d8/jsc options.  Node does not require a
    # delimeter--arguments after the filename are passed to the script.
    #
    # Check only the last part of the engine path to ensure we don't accidentally
    # label a path to nodejs containing a 'd8' as spidermonkey instead.
    jsengine = os.path.split(engine[0])[-1]
    # Use "'d8' in" because the name can vary, e.g. d8_g, d8, etc.
    return engine + [filename] + (['--'] if 'd8' in jsengine or 'jsc' in jsengine else []) + args
  
  def run_js(filename, engine=None, args=[], check_timeout=False, stdin=None, stdout=PIPE, stderr=None, cwd=None, full_output=False, assert_returncode=0, error_limit=-1):
    #  # code to serialize out the test suite files
    #  # XXX make sure to disable memory init files, and clear out the base_dir. you may also need to manually grab e.g. paper.pdf.js from a run of test_poppler
    #  import shutil, json
    #  base_dir = '/tmp/emscripten_suite'
    #  if not os.path.exists(base_dir):
    #    os.makedirs(base_dir)
    #  commands_file = os.path.join(base_dir, 'commands.txt')
    #  commands = ''
    #  if os.path.exists(commands_file):
    #    commands = open(commands_file).read()
    #  i = 0
    #  while True:
    #    curr = os.path.join(base_dir, str(i) + '.js')
    #    if not os.path.exists(curr): break
    #    i += 1
    #  shutil.copyfile(filename, curr)
    #  commands += os.path.basename(curr) + ',' + json.dumps(args) + '\n'
    #  open(commands_file, 'w').write(commands)
  
    command = make_command(filename, engine, args)
    try:
      if cwd is not None: os.environ['EMCC_BUILD_DIR'] = os.getcwd()
      proc = Popen(
          command,
          stdin=stdin,
          stdout=stdout,
          stderr=stderr,
          cwd=cwd)
    finally:
      if cwd is not None: del os.environ['EMCC_BUILD_DIR']
    timeout = 15*60 if check_timeout else None
    if TRACK_PROCESS_SPAWNS:
      logging.info('Blocking on process ' + str(proc.pid) + ': ' + str(command) + (' for ' + str(timeout) + ' seconds' if timeout else ' until it finishes.'))
    ret = timeout_run(
      proc,
      timeout,
      'Execution',
      full_output=full_output)
    if assert_returncode is not None and proc.returncode is not assert_returncode:
      raise Exception('Expected the command ' + str(command) + ' to finish with return code ' + str(assert_returncode) + ', but it returned with code ' + str(proc.returncode) + ' instead! Output: ' + str(ret)[:error_limit])
    return ret
  
  