Question

Alright, so I’m writing this program that essentially batch runs other java programs for me (multiple times, varying parameters, parallel executions, etc).

So far the running part works great. Using ProcessBuilder’s .start() method (equivalent to the Runtime.exec() I believe), it creates a separate java process and off it goes.

Problem is I would like to be able to pause/stop these processes once they’ve been started. With simple threads this is generally easy to do, however the external process doesn’t seem to have any inbuilt functionality for waiting/sleeping, at least not from an external point of view.

My question(s) is this: Is there a way to pause a java.lang.Process object? If not, does anyone know of any related exec libraries that do contain this ability? Barring all of that, is extending Process a more viable alternative?

Answer 1

You will need to create a system for sending messages between processes. You might do this by:

1. Sending signals, depending on OS. (As aioobe notes.)
2. Having one process occasionally check for presence/absence of a file that another process can create/delete. (If the file is being read/written, you will need to use file locking.)
3. Have your “main” process listen on a port, and when it launches the children it tells them (via a comamnd-line argument) how to “phone home” as they start up. Both programs alternate between doing work and checking for handling messages.

From what you have described (all Java programs in a complex batch environment) I would suggest #3, TCP/IP communication.

While it certainly involves extra work, it also gives you the flexibility to send commands or information of whatever kind you want between different processes.