On 10/26/2013 10:54 AM, Victor Polischuk wrote:
There is a quite old problem within ThreadLocal semantic which causes memory leak in case an object put in ThreadLocal has hard reference (direct or indirect) to ThreadLocal itself.
This could be considered a leak in that the spec/javadoc doesn't sufficiently emphasize that if a ThreadLocal includes a cyclic reference chain, then, in general, for a long-lived thread, you must call ThreadLocal.remove to clear it. (That is why method ThreadLocal.remove was introduced.) As you (and Andrew) point out, this is a long-standing known issue. There is also a known solution, in fact only one form of solution known to work in general: Ephemerons, basically a new, special kind of WeakReference. (Try searching "java ephemeron" for discussion on various lists and forums). It would be swell if we had them. Maybe someone could open up a JDK9 JEP for them. But short of that, as Andrew implies, nothing is known to be better than what's there. -Doug
