如何从ruby执行和管理ruby脚本？

Question

I have a script named program.rb and would like to write a script named main.rb that would do the following:

system("ruby", "program.rb")

constantly check if program.rb is running until it is done
if program.rb has reached completion
    exit main.rb
end
otherwise keep doing this until program.rb reaches completion{
if program.rb is not running and stopped before completing
    restart program.rb from where it left off
end}

I've looked into Pidify but could not find a way to apply it to fit this exactly the right way... Any help in how to approach this script would be greatly appreciated!

Update: I could figure out how to resume running the script from where it left off in program.rb if there's no way to do it in main.rb

Answer 1

It's impossible to "restart script from where it left off" without full cooperation from the program.rb . That is, it should be able to advertise its progress (by writing current state to a file, maybe?) and be able to start correctly from a step specified in ARGV. There's no external ruby magic that can replace this functionality.

Also, if a program terminated abnormally, it means one of two things:

• the error is (semi-)permanent (disk is full, no appropriate access rights to a file, etc). In this case, simply restarting the program would cause it to fail again. And again. Infinite fail loop.
• the error is temporary (shaky internet connection). In this case, program should do better job with exception handling and retry on its own (instead of terminating).

In either case, there's no need for restarting, IMHO.

Answer 2

Well, here is one way.

Modify program.rb to take an optional flag argument --restart or something.

When program.rb starts up without this argument it will initialize a file to record its current state. Periodically, it will write whatever it needs into this file to record some kind of checkpoint.

When program.rb starts up with the restart flag, it will read its checkpoint file and start processing at that point. For this to work, it must either checkpoint all state changes or arrange for all processing between checkpoints to be idempotent so it can be repeated without ill effect.

There are lots of ways to monitor the health of program.rb . The best way is with some sort of ping, perhaps something like GET /health_check or a dummy message via a socket or pipe. You could just have a locked file to detect if the lock is still held, or you could record the PID on startup and check that it still exists.