caffeine: Deadlock in NonReentrantLock

Under heavy load of JVM, we are experiencing deadlocks in caffeine version 2.5.6.

Here is the threaddump of the two threads in deadlock:

"ajp-0.0.0.0-8109-59 (P6V7aMaZbbXkfaYzYzXxID0tvHylFQJumanAAABmA)":
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000032a600bb8> (a com.github.benmanes.caffeine.cache.NonReentrantLock$Sync)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
        at com.github.benmanes.caffeine.cache.NonReentrantLock$Sync.lock(NonReentrantLock.java:315)
        at com.github.benmanes.caffeine.cache.NonReentrantLock.lock(NonReentrantLock.java:78)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.performCleanUp(BoundedLocalCache.java:1096)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.afterWrite(BoundedLocalCache.java:1017)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.put(BoundedLocalCache.java:1655)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.put(BoundedLocalCache.java:1602)
        at com.github.benmanes.caffeine.cache.LocalManualCache.put(LocalManualCache.java:64)

and

"ajp-0.0.0.0-8109-78 (-jIkyghhBePEsLll9i5dnGr65Dx8PfahGe2gAABxE)":
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000032a600bb8> (a com.github.benmanes.caffeine.cache.NonReentrantLock$Sync)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
        at com.github.benmanes.caffeine.cache.NonReentrantLock$Sync.lock(NonReentrantLock.java:315)
        at com.github.benmanes.caffeine.cache.NonReentrantLock.lock(NonReentrantLock.java:78)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.performCleanUp(BoundedLocalCache.java:1096)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.afterWrite(BoundedLocalCache.java:1017)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.put(BoundedLocalCache.java:1655)
        at com.github.benmanes.caffeine.cache.BoundedLocalCache.put(BoundedLocalCache.java:1602)
        at com.github.benmanes.caffeine.cache.LocalManualCache.put(LocalManualCache.java:64)

Looking at the code, I can’t imagine a scenario this could occur, but it does occur under heavy load of our JVMs.

Any ideas what we could do? For now, as a workaround, I’ve added a synchronized() block around the cache.put() methods to make sure only 1 thread is adding new values to the cache at a time.