function onClose( child ) {
		return listener;

		/**
		* Callback invoked upon child process close.
		*
		* @private
		* @param {(number|null)} code - exit code
		* @param {(string|null)} signal - termination signal
		*/
		function listener( code, signal ) {
			debug( 'Child process closed. Code: %d. Signal: %s. pid: %d.', code, signal, child.pid );
			processExit( code, signal );
			childClosed();
		}
	}
Returns a callback to be invoked upon child process close.

@private
@param {Object} child - child process
@returns {Callback} callback