This option disables the fat lock spin code in Java, allowing threads that block trying to acquire a fat lock go to sleep directly.
Objects in Java become a lock as soon as any thread enters a synchronized block on that object. All locks are held (that is, stayed locked) until released by the locking thread. If the lock is not going to be released very fast, it can be inflated to a “fat lock.” “Spinning” occurs when a thread that wants a specific lock continuously checks that lock to see if it is still taken, spinning in a tight loop as it makes the check. Spinning against a fat lock is generally beneficial although, in some instances, it can be expensive and might affect performance.
-XXdisableFatSpin allows you to turn off spinning against a fat lock and eliminate the potential performance hit.