Comments on: Java Concurrency Bugs #1 – mutable statics

By: Chris Dennis

Chris Dennis — Tue, 27 Jan 2009 23:12:08 +0000

Another small tool that can be useful here is Bill Pugh's checked-uncontended-lock. It allows you to 'assert' that a lock is uncontended. Of course just because you don't see any contention doesn't mean there won't be any in the future.

By: Peter Veentjer

Peter Veentjer — Tue, 27 Jan 2009 21:52:11 +0000

In essence all solution are based on one of the 3 following:
- immutability
- isolation (confinement)
- synchronisation

Last year I created a small tool that used bytecode instrumentation to do runtime analysis of concurrent access on objects, just to figure out where to start looking:
http://concurrency-detector.googlecode.com/

By: Alex

Alex — Tue, 27 Jan 2009 20:43:54 +0000

Yep, ThreadLocal is a special case of thread confinement and a good way to solve the particular case of Calendar/SimpleDateFormat since they have no state that actually should be shared across threads.

By: Matthew Hall

Matthew Hall — Tue, 27 Jan 2009 20:25:55 +0000

Another option is to use a static ThreadLocal so that each thread gets their own instance.

private static final ThreadLocal calendar = new ThreadLocal() { public Calendar initialValue() { return Calendar.getInstance(); } }; public static Calendar getCalendar() { return calendar.get(); }