With change https://git.eclipse.org/r/c/jgit/jgit/+/186455 a thread
loading a bitmap index could hold two ref locks at the same time (one
for bitmap and one for either index or reverse index). So it is possible
that two threads loading bitmaps end up in a deadlock for ref locks e.g.
threadA has refLock[1] (for bitmap) and wants refLock[2] (for index or
revIndex) and threadB has refLock[2] (for bitmap) and wants refLock[1].
This change introduces separate pools of locks per pack extension
instead of a shared pool. So threads loading bitmap can hold two
locks but with different extensions and no overlap, e.g. threadA holds
refLock[BITMAP_INDEX][1] and refLock[INDEX][2] and threadB holds
refLock[BITMAP_INDEX][2] and refLock[INDEX][1].
More unit tests were added to cover various paralell loading scenarios.
Signed-off-by: Alina Djamankulova <adjama@google.com>
Change-Id: I89704b4721c21548929608d3798ef60925280755
49d243b13c