Fix thread local fallback initialization (#515)

Author: ben-manes

caffeine/src/main/java/com/github/benmanes/caffeine/cache/StripedBuffer.java

@@ -340,7 +340,7 @@ static final class VarHandleProbe implements Probe {
 
   /** Uses a thread local to maintain a random probe value. */
   static final class ThreadLocalProbe implements Probe {
-    static final ThreadLocal<int[]> threadHashCode = new ThreadLocal<>();
+    static final ThreadLocal<int[]> threadHashCode = ThreadLocal.withInitial(() -> new int[1]);
 
     @Override public int get() {
       return threadHashCode.get()[0];
@@ -351,7 +351,7 @@ static final class ThreadLocalProbe implements Probe {
     @Override public void initialize() {
       // Avoid zero to allow xorShift rehash
       int hash = 1 | ThreadLocalRandom.current().nextInt();
-      threadHashCode.set(new int[] { hash });
+      threadHashCode.get()[0] = hash;
     }
   }
 }

caffeine/src/test/java/com/github/benmanes/caffeine/cache/StripedBufferTest.java

@@ -49,6 +49,7 @@ public void init(FakeBuffer<Integer> buffer) {
 
   @Test(dataProvider = "probes")
   public void probe(Probe probe) {
+    probe.get();
     probe.initialize();
     assertThat(probe.get(), is(not(0)));