Module: ShellTest::ShellMethods::Utils

Included in:
Session
Defined in:
lib/shell_test/shell_methods/utils.rb

Class Method Summary collapse

Class Method Details

.spawn(cmd, log = []) ⇒ Object

Spawns a PTY session and returns the Process::Status for the session upon completion. The PTY process is killed upon an unhandled error (but the error is re-raised for further handling).

Note that $? is set by spawn but is not reliable until 1.9.2 (ish). Prior to that PTY used a cleanup thread that would wait on a spawned process and raise a PTY::ChildExited error in some cases. As a result manual calls to Process.wait (which would set $?) cause a race condition. Rely on the output of spawn instead.



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# File 'lib/shell_test/shell_methods/utils.rb', line 17

def spawn(cmd, log=[])
  # The race condition described above actually applies to both kill and
  # wait which raise Errno::ESRCH or Errno::ECHILD if they lose the
  # race.  This code is designed to capture those errors if they occur
  # and then give the cleanup thread a chance to take over; eventually
  # it will raise a ChildExited error.  This is a sketchy use of
  # exceptions for flow control but there is little option - a
  # consequence of PTY using threads with side effects.
  PTY.spawn(cmd) do |slave, master, pid|
    begin
      yield(master, slave)

      begin
        Process.wait(pid)
      rescue Errno::ECHILD
        Thread.pass
        raise
      end

    rescue PTY::ChildExited
      # This is the 'normal' exit route on 1.8.6 and 1.8.7.
      return $!.status

    rescue Exception => error
      begin

        # Manually cleanup the pid on error.  This code no longer cares
        # what exactly happens to $? - the point is to make sure the
        # child doesn't become a zombie and then re-raise the error.
        begin
          Process.kill(9, pid)
        rescue Errno::ESRCH
          Thread.pass
          raise
        end

        # Clearing the slave allows quicker exits on OS X.
        while IO.select([slave],nil,nil,0.1)
          begin
            break unless slave.read(1)
          rescue Errno::EIO
            # On some linux (ex ubuntu) read can return an eof or fail with
            # an EIO error when a terminal disconnect occurs and an EIO
            # condition occurs - the exact behavior is unspecified but the
            # meaning is the same... no more data is available, so break.
            break
          end
        end

        begin
          Process.wait(pid)
        rescue Errno::ECHILD
          Thread.pass
          raise
        end

      rescue PTY::ChildExited
        # The cleanup thread could finish at any point in the rescue
        # handling so account for that here.
      ensure
        raise error
      end
    end
  end

  $?
end