Add FastFlow-based buffer strategy

caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/BufferType.java

@@ -24,6 +24,7 @@
  */
 public enum BufferType {
   Ticket(TicketBuffer::new),
+  FastFlow(FastFlowBuffer::new),
   ManyToOne(ManyToOneBuffer::new),
   MpscArray(MpscArrayBuffer::new),
   MpmcArray(MpmcArrayBuffer::new),

caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/FastFlowBuffer.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2015 Ben Manes. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.github.benmanes.caffeine.cache.buffer;
+
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.Lock;
+
+import javax.annotation.concurrent.GuardedBy;
+
+import org.jctools.queues.MpscArrayQueue;
+
+import com.github.benmanes.caffeine.locks.NonReentrantLock;
+
+/**
+ * A ring buffer implemented using the FastFlow technique.
+ * <p>
+ * This is an adaption of the {@link MpscArrayQueue} where the padding has been stripped off. The
+ * lower throughput is offset by the reduced memory overhead.
+ *
+ * @author [email protected] (Ben Manes)
+ */
+final class FastFlowBuffer implements Buffer {
+  final Lock evictionLock;
+
+  final AtomicLong readCache;
+  final AtomicLong readCounter;
+  final AtomicLong writeCounter;
+  final AtomicReference<Object>[] buffer;
+
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  FastFlowBuffer() {
+    readCache = new AtomicLong();
+    readCounter = new AtomicLong();
+    writeCounter = new AtomicLong();
+    evictionLock = new NonReentrantLock();
+    buffer = new AtomicReference[MAX_SIZE];
+    for (int i = 0; i < MAX_SIZE; i++) {
+      buffer[i] = new AtomicReference<>();
+    }
+  }
+
+  @Override
+  public boolean record() {
+    long tail = writeCounter.get();
+    long headCache = readCache.get();
+    long wrap = tail - MAX_SIZE;
+
+    if (headCache <= wrap) {
+      long head = readCounter.get();
+      if (head <= wrap) {
+        return true;
+      }
+      readCache.lazySet(head);
+    }
+
+    if (writeCounter.compareAndSet(tail, tail + 1)) {
+      int index = (int) (tail & MAX_SIZE_MASK);
+      buffer[index].lazySet(Boolean.TRUE);
+    }
+    return false;
+  }
+
+  @Override
+  public void drain() {
+    if (evictionLock.tryLock()) {
+      drainUnderLock();
+      evictionLock.unlock();
+    }
+  }
+
+  @GuardedBy("evictionLock")
+  private void drainUnderLock() {
+    long head = readCounter.get();
+
+    for (;;) {
+      int index = (int) (head & MAX_SIZE_MASK);
+      if (buffer[index].get() == null) {
+        // empty or not published yet
+        break;
+      }
+      buffer[index].lazySet(null);
+      head++;
+    }
+    readCounter.lazySet(head);
+  }
+
+  @Override
+  public long recorded() {
+    return writeCounter.get();
+  }
+
+  @Override
+  public long drained() {
+    evictionLock.lock();
+    drainUnderLock();
+    evictionLock.unlock();
+    return readCounter.get();
+  }
+}