Java while loop and Threads! [duplicate]

Question

I have a program that continually polls the database for change in value of some field. It runs in the background and currently uses a while(true) and a sleep() method to set the interval. I am wondering if this is a good practice? And, what could be a more efficient way to implement this? The program is meant to run at all times.

Consequently, the only way to stop the program is by issuing a kill on the process ID. The program could be in the middle of a JDBC call. How could I go about terminating it more gracefully? I understand that the best option would be to devise some kind of exit strategy by using a flag that will be periodically checked by the thread. But, I am unable to think of a way/condition of changing the value of this flag. Any ideas?

Answer 1

I am wondering if this is a good practice?

No. It's not good. Sometimes, it's all you've got, but it's not good.

And, what could be a more efficient way to implement this?

How do things get into the database in the first place?

The best change is to fix programs that insert/update the database to make requests which go to the database and to your program. A JMS topic is good for this kind of thing.

The next best change is to add a trigger to the database to enqueue each insert/update event into a queue. The queue could feed a JMS topic (or queue) for processing by your program.

The fall-back plan is your polling loop.

Your polling loop, however, should not trivially do work. It should drop a message into a queue for some other JDBC process to work on. A termination request is another message that can be dropped into the JMS queue. When your program gets the termination message, it absolutely must be finished with the prior JDBC request and can stop gracefully.

Before doing any of this, look at ESB solutions. Sun's JCAPS or TIBCO already have this. An open source ESB like Mulesource or Jitterbit may already have this functionality already built and tested.

Answer 2

This is really too big an issue to answer completely in this format. Do yourself a favour and go buy Java Concurrency in Practice. There is no better resource for concurrency on the Java 5+ platform out there. There are whole chapters devoted to this subject.

On the subject of killing your process during a JDBC call, that should be fine. I believe there are issues with interrupting a JDBC call (in that you can't?) but that's a different issue.