Keep track of a static collection of all PackWriter instances

Stored in a weak concurrent hash map, which we clean up while iterating.
Usually the weak reference behavior should not be necessary because
PackWriters should be released with release(), but we still want to
avoid leaks when dealing with broken client code.

Change-Id: I337abb952ac6524f7f920fedf04065edf84d01d2
1 file changed