Sleep Interrupted

I’m currently using optimistic locking to implement a bulk-upload use-case with low concurrency requirements. The uploaded “numbers” simply need to be matched, one-to-one, with any unused “aliases” already present in the database. The optimistic locking is in the form of a “version” field on the “alias” that gets incremented when the “alias” is assigned to a “number”. The easiest way that springs to mind to handle the potential optimistic locking version conflict of concurrent access is to retry n times, sleeping a tiny bit in between. As a side note, if there’s a better way to approach optimistic locking recovery in this rare case where no user input is required, and the system can rationally try something different on every retry, I’d like to know about it.

In the meantime, I’m befriending Thread.sleep(), and I’m reminded of the importance of handling the InterruptedException properly. By far the most common approach is to simply ignore the exception and carry on immediately from where it was caught. The problem with this is that the most likely reason your thread might be getting interrupted is if the application is trying to shut down. Imagine your optimistic locking retry loop is set to retry 10 times, waiting 100ms each time (since it’s low concurrency, and highly unlikely it will have to retry ever, let alone more than once), and ignoring interruptions. On application shutdown, if this loop has only just begun, its first sleep will be interrupted, but that leaves it with 900ms of sleep left to go before it will shut down. That’s likely to cause some issues regarding unclean shutdown of that thread.

So if you get interrupted in a loop while waiting for something, your best bet is to respond by throwing an exception. The way I see it, your options are to “throws” the InterruptedException and don’t bother catching it, requiring callers of your method to catch it and hope they deal with it nicely (this is probably the right approach for library code), or choose an application-specific runtime exception which is obviously terminal so that no other part of the application will attempt to catch it and handle it. Roll back your transactions and walk away.