retry.py

retry.py

#! /usr/bin/env python3

import sys, os, argparse, subprocess, time


class UserError(Exception):
	def __init__(self, msg, *args):
		super().__init__(msg.format(*args))


def log(msg, *args):
	print('{}: {}'.format(os.path.basename(sys.argv[0]), msg.format(*args)), file = sys.stderr)


def parse_args():
	parser = argparse.ArgumentParser()
	
	parser.add_argument('command', nargs = argparse.REMAINDER, help = 'Command to execute.')
	parser.add_argument('-i', '--min-interval', type = float, default = 10, help = 'Minimum time in seconds since the command has been started the last time before it is started again. Defaults to 10 seconds.')
	parser.add_argument('-w', '--min-wait', type = float, default = 0, help = 'Minimum time in seconds after the command has terminated before it is started again. Defaults to no wait time.')
	parser.add_argument('-r', '--restart-always', action = 'store_const', dest = 'restart', const = 'always', help = 'Restart the command whether it completes successfully or with a failure. By default, the command is only restarted until it succeeds.')
	parser.add_argument('-R', '--restart-on-success', action = 'store_const', dest = 'restart', const = 'success', help = 'Restart the command as long as it succeeds.')
	
	return parser.parse_args()


def main():
	args = parse_args()
	
	start_time = 0
	min_wait = 0
	
	while True:
		current_time = time.time()
		start_time = max(start_time + args.min_interval, current_time + min_wait)
		wait_time = start_time - current_time 
		
		if wait_time > 0:
			log('Waiting {:.1f} seconds before restarting the command.', wait_time)
			
			time.sleep(wait_time)
		else:
			start_time = current_time
		
		process = subprocess.Popen(args.command)
		process.wait()
		
		if process.returncode:		
			log('Process exited with status {}.', process.returncode)
			
			if args.restart == 'success':
				raise UserError('Command failed with exit code {}.', process.returncode)
		else:
			if not args.restart:
				break
		
		min_wait = args.min_wait


try:
	main()
except UserError as e:
	log('Error: {}', e)
	sys.exit(1)
except KeyboardInterrupt:
	log('Operation interrupted.')
	sys.exit(2)