Class DisposableThreadLocal<T>

Java's builtin ThreadLocal has a serious flaw: it can take an arbitrarily long amount of time to dereference the things you had stored in it, even once the ThreadLocal instance itself is no longer referenced. This is because there is single, master map stored for each thread, which all ThreadLocals share, and that master map only periodically purges "stale" entries.

While not technically a memory leak, because eventually the memory will be reclaimed, it can take a long time and you can easily hit because from the GC's standpoint the stale entries are not reclaimable.

This class works around that, by only enrolling WeakReference values into the ThreadLocal, and separately holding a hard reference to each stored value. When you call Dispose(), these hard references are cleared and then GC is freely able to reclaim space by objects stored in it.

You should not call Dispose() until all threads are done using the instance.

@lucene.internal