Public Enemy No.1

Alex Miller aka Pure Danger Tech has a great entry on most common concurrency bugs.

the timing is perfect – this very thing bit me today. long story short, an old app, previously perceived to be multi-threaded, was recently converted to actually be multi-threaded, and then, once traffic ramped up a bit, exhibited peculiar behavior when perfectly good dates could not be parsed. thank god it blew up, as opposed to quietly corrupting the data.

so something as innocent-looking as private static final SimpleDateFormat declaration was the culprit: java.text.DateFormat is not thread-safe.

luckily, it is easy enough to spot and reproduce (threadPoolSize and invocationCount in TestNG simplify it even further).

a pessimist would heave a mighty sigh, once again swear on the copy of JCIP to find and root out every frivolous static out there with the help of FindBugs or a simple regex.

meanwhile, there is joda-time and a promise of jsr310

but of course this whole experience still leaves you feeling cheated and dirty – why, god, why?! something so function-like and stateless in nature insists on stowing things away.