Merge changes Ibb3467f7,I2af99903

* changes:
  Always use try/finally around DfsBlockCache.clockLock
  DfsBlockCache: Fix NPE when evicting empty cell

org.eclipse.jgit/src/org/eclipse/jgit/storage/dfs/DfsBlockCache.java

@@ -206,7 +206,7 @@ public final class DfsBlockCache {
 		blockSizeShift = Integer.numberOfTrailingZeros(blockSize);
 
 		clockLock = new ReentrantLock(true /* fair */);
-		clockHand = new Ref<Object>(null, -1, 0, null);
+		clockHand = new Ref<Object>(new DfsPackKey(), -1, 0, null);
 		clockHand.next = clockHand;
 
 		readAheadLimit = cfg.getReadAheadLimit();
@@ -389,6 +389,7 @@ public final class DfsBlockCache {
 	@SuppressWarnings("unchecked")
 	private void reserveSpace(int reserve) {
 		clockLock.lock();
+		try {
 			long live = liveBytes + reserve;
 			if (maxBytes < live) {
 				Ref prev = clockHand;
@@ -418,8 +419,10 @@ public final class DfsBlockCache {
 				clockHand = prev;
 			}
 			liveBytes = live;
+		} finally {
 			clockLock.unlock();
 		}
+	}
 
 	private void creditSpace(int credit) {
 		clockLock.lock();
@@ -429,14 +432,17 @@ public final class DfsBlockCache {
 
 	private void addToClock(Ref ref, int credit) {
 		clockLock.lock();
+		try {
 			if (credit != 0)
 				liveBytes -= credit;
 			Ref ptr = clockHand;
 			ref.next = ptr.next;
 			ptr.next = ref;
 			clockHand = ref;
+		} finally {
 			clockLock.unlock();
 		}
+	}
 
 	void put(DfsBlock v) {
 		put(v.pack, v.start, v.size(), v);