Let PoolThreadCache work even if allocation and deallocation Thread are different

Motivation:

PoolThreadCache did only cache allocations if the allocation and deallocation Thread were the same. This is not optimal as often people write from differen thread then the actual EventLoop thread.

Modification:

- Add MpscArrayQueue which was forked from jctools and lightly modified.
- Use MpscArrayQueue for caches and always add buffer back to the cache that belongs to the allocation thread.

Result:

ThreadPoolCache is now also usable and so gives performance improvements when allocation and deallocation thread are different.

Performance when using same thread for allocation and deallocation is noticable worse then before.

NOTICE.txt

@@ -98,6 +98,14 @@ a constant-size alphabet written by Yuta Mori. It can be obtained at:
   * HOMEPAGE:
     * https://code.google.com/p/libdivsufsort/
 
+This product contains a modified portion of Nitsan Wakart's 'JCTools', Java Concurrency Tools for the JVM,
+ which can be obtained at:
+
+  * LICENSE:
+    * license/LICENSE.jctools.txt (ASL2 License)
+  * HOMEPAGE:
+    * https://github.com/JCTools/JCTools
+
 This product optionally depends on 'JZlib', a re-implementation of zlib in
 pure Java, which can be obtained at:
 

buffer/src/main/java/io/netty/buffer/PoolArena.java

@@ -237,19 +237,17 @@ abstract class PoolArena<T> implements PoolArenaMetric {
         buf.initUnpooled(newUnpooledChunk(reqCapacity), reqCapacity);
     }
 
-    void free(PoolChunk<T> chunk, long handle, int normCapacity, boolean sameThreads) {
+    void free(PoolChunk<T> chunk, long handle, int normCapacity, PoolThreadCache cache) {
         if (chunk.unpooled) {
             allocationsHuge.decrement();
             destroyChunk(chunk);
         } else {
             SizeClass sizeClass = sizeClass(normCapacity);
-            if (sameThreads) {
+            if (cache != null && cache.add(this, chunk, handle, normCapacity, sizeClass)) {
-                PoolThreadCache cache = parent.threadCache();
+                // cached so not free it.
-                if (cache.add(this, chunk, handle, normCapacity, sizeClass)) {
+                return;
-                    // cached so not free it.
-                    return;
-                }
             }
+
             freeChunk(chunk, handle, sizeClass);
         }
     }
@@ -378,7 +376,7 @@ abstract class PoolArena<T> implements PoolArenaMetric {
         buf.setIndex(readerIndex, writerIndex);
 
         if (freeOldMemory) {
-            free(oldChunk, oldHandle, oldMaxLength, buf.initThread == Thread.currentThread());
+            free(oldChunk, oldHandle, oldMaxLength, buf.cache);
         }
     }
 

buffer/src/main/java/io/netty/buffer/PoolChunk.java

@@ -358,7 +358,8 @@ final class PoolChunk<T> implements PoolChunkMetric {
         if (bitmapIdx == 0) {
             byte val = value(memoryMapIdx);
             assert val == unusable : String.valueOf(val);
-            buf.init(this, handle, runOffset(memoryMapIdx), reqCapacity, runLength(memoryMapIdx));
+            buf.init(this, handle, runOffset(memoryMapIdx), reqCapacity, runLength(memoryMapIdx),
+                     arena.parent.threadCache());
         } else {
             initBufWithSubpage(buf, handle, bitmapIdx, reqCapacity);
         }
@@ -379,7 +380,8 @@ final class PoolChunk<T> implements PoolChunkMetric {
 
         buf.init(
             this, handle,
-            runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize);
+            runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize,
+            arena.parent.threadCache());
     }
 
     private byte value(int id) {

buffer/src/main/java/io/netty/buffer/PoolThreadCache.java

@@ -18,11 +18,15 @@ package io.netty.buffer;
 
 
 import io.netty.buffer.PoolArena.SizeClass;
+import io.netty.util.Recycler;
+import io.netty.util.Recycler.Handle;
 import io.netty.util.ThreadDeathWatcher;
+import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
 import java.nio.ByteBuffer;
+import java.util.Queue;
 
 /**
  * Acts a Thread cache for allocations. This implementation is moduled after
@@ -116,11 +120,11 @@ final class PoolThreadCache {
         ThreadDeathWatcher.watch(thread, freeTask);
     }
 
-    private static <T> SubPageMemoryRegionCache<T>[] createSubPageCaches(
+    private static <T> MemoryRegionCache<T>[] createSubPageCaches(
             int cacheSize, int numCaches, SizeClass sizeClass) {
         if (cacheSize > 0) {
             @SuppressWarnings("unchecked")
-            SubPageMemoryRegionCache<T>[] cache = new SubPageMemoryRegionCache[numCaches];
+            MemoryRegionCache<T>[] cache = new MemoryRegionCache[numCaches];
             for (int i = 0; i < cache.length; i++) {
                 // TODO: maybe use cacheSize / cache.length
                 cache[i] = new SubPageMemoryRegionCache<T>(cacheSize, sizeClass);
@@ -131,14 +135,14 @@ final class PoolThreadCache {
         }
     }
 
-    private static <T> NormalMemoryRegionCache<T>[] createNormalCaches(
+    private static <T> MemoryRegionCache<T>[] createNormalCaches(
             int cacheSize, int maxCachedBufferCapacity, PoolArena<T> area) {
         if (cacheSize > 0) {
             int max = Math.min(area.chunkSize, maxCachedBufferCapacity);
             int arraySize = Math.max(1, log2(max / area.pageSize) + 1);
 
             @SuppressWarnings("unchecked")
-            NormalMemoryRegionCache<T>[] cache = new NormalMemoryRegionCache[arraySize];
+            MemoryRegionCache<T>[] cache = new MemoryRegionCache[arraySize];
             for (int i = 0; i < cache.length; i++) {
                 cache[i] = new NormalMemoryRegionCache<T>(cacheSize);
             }
@@ -345,28 +349,15 @@ final class PoolThreadCache {
         }
     }
 
-    /**
-     * Cache of {@link PoolChunk} and handles which can be used to allocate a buffer without locking at all.
-     *
-     * The {@link MemoryRegionCache} uses a LIFO implementation as this way it is more likely that the
-     * cached memory is still in the loaded cache-line and so no new read must happen (compared to FIFO).
-     */
     private abstract static class MemoryRegionCache<T> {
-        private final Entry<T>[] entries;
+        private final int size;
+        private final Queue<Entry<T>> queue;
         private final SizeClass sizeClass;
-        private final int maxUnusedCached;
+        private int allocations;
-        private int head;
-        private int tail;
-        private int maxEntriesInUse;
-        private int entriesInUse;
 
-        @SuppressWarnings("unchecked")
         MemoryRegionCache(int size, SizeClass sizeClass) {
-            entries = new Entry[powerOfTwo(size)];
+            this.size = powerOfTwo(size);
-            for (int i = 0; i < entries.length; i++) {
+            queue = PlatformDependent.newFixedMpscQueue(this.size);
-                entries[i] = new Entry<T>();
-            }
-            maxUnusedCached = size / 2;
             this.sizeClass = sizeClass;
         }
 
@@ -393,115 +384,100 @@ final class PoolThreadCache {
         /**
          * Add to cache if not already full.
          */
-        public boolean add(PoolChunk<T> chunk, long handle) {
+        @SuppressWarnings("unchecked")
-            Entry<T> entry = entries[tail];
+        public final boolean add(PoolChunk<T> chunk, long handle) {
-            if (entry.chunk != null) {
+            return queue.offer(newEntry(chunk, handle));
-                // cache is full
-                return false;
-            }
-            entriesInUse --;
-
-            entry.chunk = chunk;
-            entry.handle = handle;
-            tail = nextIdx(tail);
-            return true;
         }
 
         /**
          * Allocate something out of the cache if possible and remove the entry from the cache.
          */
-        public boolean allocate(PooledByteBuf<T> buf, int reqCapacity) {
+        public final boolean allocate(PooledByteBuf<T> buf, int reqCapacity) {
-            int index = prevIdx(tail);
+            Entry<T> entry = queue.poll();
-            Entry<T> entry = entries[index];
+            if (entry == null) {
-            if (entry.chunk == null) {
                 return false;
             }
-
-            entriesInUse ++;
-            if (maxEntriesInUse < entriesInUse) {
-                maxEntriesInUse = entriesInUse;
-            }
             initBuf(entry.chunk, entry.handle, buf, reqCapacity);
-            // only null out the chunk as we only use the chunk to check if the buffer is full or not.
+
-            entry.chunk = null;
+            // allocations is not thread-safe which is fine as this is only called from the same thread all time.
-            tail = index;
+            ++ allocations;
             return true;
         }
 
         /**
          * Clear out this cache and free up all previous cached {@link PoolChunk}s and {@code handle}s.
          */
-        public int free() {
+        public final int free() {
+            return free(Integer.MAX_VALUE);
+        }
+
+        private int free(int max) {
             int numFreed = 0;
-            entriesInUse = 0;
+            for (; numFreed < max; numFreed++) {
-            maxEntriesInUse = 0;
+                Entry<T> entry = queue.poll();
-            for (int i = head;; i = nextIdx(i)) {
+                if (entry != null) {
-                if (freeEntry(entries[i])) {
+                    freeEntry(entry);
-                    numFreed++;
                 } else {
                     // all cleared
                     return numFreed;
                 }
             }
+            return numFreed;
         }
 
         /**
          * Free up cached {@link PoolChunk}s if not allocated frequently enough.
          */
-        private void trim() {
+        public final void trim() {
-            int free = size() - maxEntriesInUse;
+            int free = size - allocations;
-            entriesInUse = 0;
+            allocations = 0;
-            maxEntriesInUse = 0;
 
-            if (free <= maxUnusedCached) {
+            // We not even allocated all the number that are
-                return;
+            if (free > 0) {
+                free(free);
             }
-
-            int i = head;
-            for (; free > 0; free--) {
-                if (!freeEntry(entries[i])) {
-                    // all freed
-                    break;
-                }
-                i = nextIdx(i);
-            }
-
-            // Update head to point to te correct entry
-            // See https://github.com/netty/netty/issues/2924
-            head = i;
         }
 
         @SuppressWarnings({ "unchecked", "rawtypes" })
-        private boolean freeEntry(Entry entry) {
+        private  void freeEntry(Entry entry) {
             PoolChunk chunk = entry.chunk;
-            if (chunk == null) {
+
-                return false;
+            // recycle now so PoolChunk can be GC'ed.
-            }
+            entry.recycle();
+
             chunk.arena.freeChunk(chunk, entry.handle, sizeClass);
-            entry.chunk = null;
-            return true;
         }
 
-        /**
+        static final class Entry<T> {
-         * Return the number of cached entries.
+            final Handle recyclerHandle;
-         */
-        private int size()  {
-            return tail - head & entries.length - 1;
-        }
-
-        private int nextIdx(int index) {
-            // use bitwise operation as this is faster as using modulo.
-            return index + 1 & entries.length - 1;
-        }
-
-        private int prevIdx(int index) {
-            // use bitwise operation as this is faster as using modulo.
-            return index - 1 & entries.length - 1;
-        }
-
-        private static final class Entry<T> {
             PoolChunk<T> chunk;
-            long handle;
+            long handle = -1;
+
+            Entry(Handle recyclerHandle) {
+                this.recyclerHandle = recyclerHandle;
+            }
+
+            void recycle() {
+                chunk = null;
+                handle = -1;
+                RECYCLER.recycle(this, recyclerHandle);
+            }
         }
+
+        @SuppressWarnings("rawtypes")
+        private static Entry newEntry(PoolChunk<?> chunk, long handle) {
+            Entry entry = RECYCLER.get();
+            entry.chunk = chunk;
+            entry.handle = handle;
+            return entry;
+        }
+
+        @SuppressWarnings("rawtypes")
+        private static final Recycler<Entry> RECYCLER = new Recycler<Entry>() {
+            @Override
+            protected Entry newObject(Handle handle) {
+                return new Entry(handle);
+            }
+        };
     }
 }

buffer/src/main/java/io/netty/buffer/PooledByteBuf.java

@@ -32,7 +32,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
     protected int offset;
     protected int length;
     int maxLength;
-    Thread initThread;
+    PoolThreadCache cache;
     private ByteBuffer tmpNioBuf;
 
     @SuppressWarnings("unchecked")
@@ -41,7 +41,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
         this.recyclerHandle = (Handle<PooledByteBuf<T>>) recyclerHandle;
     }
 
-    void init(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength) {
+    void init(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength, PoolThreadCache cache) {
         assert handle >= 0;
         assert chunk != null;
 
@@ -54,7 +54,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
         setIndex(0, 0);
         discardMarks();
         tmpNioBuf = null;
-        initThread = Thread.currentThread();
+        this.cache = cache;
     }
 
     void initUnpooled(PoolChunk<T> chunk, int length) {
@@ -67,7 +67,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
         this.length = maxLength = length;
         setIndex(0, 0);
         tmpNioBuf = null;
-        initThread = Thread.currentThread();
+        cache = null;
     }
 
     @Override
@@ -155,9 +155,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
             final long handle = this.handle;
             this.handle = -1;
             memory = null;
-            boolean sameThread = initThread == Thread.currentThread();
+            chunk.arena.free(chunk, handle, maxLength, cache);
-            initThread = null;
-            chunk.arena.free(chunk, handle, maxLength, sameThread);
             recycle();
         }
     }

buffer/src/main/java/io/netty/buffer/PooledUnsafeDirectByteBuf.java

@@ -16,6 +16,7 @@
 
 package io.netty.buffer;
 
+import io.netty.buffer.PooledByteBufAllocator.PoolThreadLocalCache;
 import io.netty.util.Recycler;
 import io.netty.util.internal.PlatformDependent;
 
@@ -53,8 +54,9 @@ final class PooledUnsafeDirectByteBuf extends PooledByteBuf<ByteBuffer> {
     }
 
     @Override
-    void init(PoolChunk<ByteBuffer> chunk, long handle, int offset, int length, int maxLength) {
+    void init(PoolChunk<ByteBuffer> chunk, long handle, int offset, int length, int maxLength,
-        super.init(chunk, handle, offset, length, maxLength);
+              PoolThreadCache cache) {
+        super.init(chunk, handle, offset, length, maxLength, cache);
         initMemoryAddress();
     }
 

common/src/main/java/io/netty/util/internal/ConcurrentCircularArrayQueue.java

@@ -0,0 +1,207 @@
+/*
+ * Copyright 2015 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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.
+ */
+/*
+ * 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 io.netty.util.internal;
+
+
+import java.util.AbstractQueue;
+import java.util.Iterator;
+
+/**
+ * Forked from <a href="https://github.com/JCTools/JCTools">JCTools</a>.
+ *
+ * A concurrent access enabling class used by circular array based queues this class exposes an offset computation
+ * method along with differently memory fenced load/store methods into the underlying array. The class is pre-padded and
+ * the array is padded on either side to help with False sharing prvention. It is expected theat subclasses handle post
+ * padding.
+ * <p>
+ * Offset calculation is separate from access to enable the reuse of a give compute offset.
+ * <p>
+ * Load/Store methods using a <i>buffer</i> parameter are provided to allow the prevention of final field reload after a
+ * LoadLoad barrier.
+ * <p>
+ *
+ * @param <E>
+ */
+abstract class ConcurrentCircularArrayQueue<E> extends ConcurrentCircularArrayQueueL0Pad<E> {
+    protected static final int REF_BUFFER_PAD;
+    private static final long REF_ARRAY_BASE;
+    private static final int REF_ELEMENT_SHIFT;
+    static {
+        final int scale = PlatformDependent0.UNSAFE.arrayIndexScale(Object[].class);
+        if (4 == scale) {
+            REF_ELEMENT_SHIFT = 2;
+        } else if (8 == scale) {
+            REF_ELEMENT_SHIFT = 3;
+        } else {
+            throw new IllegalStateException("Unknown pointer size");
+        }
+        // 2 cache lines pad
+        // TODO: replace 64 with the value we can detect
+        REF_BUFFER_PAD = (64 * 2) / scale;
+        // Including the buffer pad in the array base offset
+        REF_ARRAY_BASE = PlatformDependent0.UNSAFE.arrayBaseOffset(Object[].class) + (REF_BUFFER_PAD * scale);
+    }
+    protected final long mask;
+    // @Stable :(
+    protected final E[] buffer;
+
+    @SuppressWarnings("unchecked")
+    public ConcurrentCircularArrayQueue(int capacity) {
+        int actualCapacity = roundToPowerOfTwo(capacity);
+        mask = actualCapacity - 1;
+        // pad data on either end with some empty slots.
+        buffer = (E[]) new Object[actualCapacity + REF_BUFFER_PAD * 2];
+    }
+
+    private static int roundToPowerOfTwo(final int value) {
+        return 1 << (32 - Integer.numberOfLeadingZeros(value - 1));
+    }
+    /**
+     * @param index desirable element index
+     * @return the offset in bytes within the array for a given index.
+     */
+    protected final long calcElementOffset(long index) {
+        return calcElementOffset(index, mask);
+    }
+    /**
+     * @param index desirable element index
+     * @param mask
+     * @return the offset in bytes within the array for a given index.
+     */
+    protected static final long calcElementOffset(long index, long mask) {
+        return REF_ARRAY_BASE + ((index & mask) << REF_ELEMENT_SHIFT);
+    }
+    /**
+     * A plain store (no ordering/fences) of an element to a given offset
+     *
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @param e a kitty
+     */
+    protected final void spElement(long offset, E e) {
+        spElement(buffer, offset, e);
+    }
+
+    /**
+     * A plain store (no ordering/fences) of an element to a given offset
+     *
+     * @param buffer this.buffer
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @param e an orderly kitty
+     */
+    protected static final <E> void spElement(E[] buffer, long offset, E e) {
+        PlatformDependent0.UNSAFE.putObject(buffer, offset, e);
+    }
+
+    /**
+     * An ordered store(store + StoreStore barrier) of an element to a given offset
+     *
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @param e an orderly kitty
+     */
+    protected final void soElement(long offset, E e) {
+        soElement(buffer, offset, e);
+    }
+
+    /**
+     * An ordered store(store + StoreStore barrier) of an element to a given offset
+     *
+     * @param buffer this.buffer
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @param e an orderly kitty
+     */
+    protected static final <E> void soElement(E[] buffer, long offset, E e) {
+        PlatformDependent0.UNSAFE.putOrderedObject(buffer, offset, e);
+    }
+
+    /**
+     * A plain load (no ordering/fences) of an element from a given offset.
+     *
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @return the element at the offset
+     */
+    protected final E lpElement(long offset) {
+        return lpElement(buffer, offset);
+    }
+
+    /**
+     * A plain load (no ordering/fences) of an element from a given offset.
+     *
+     * @param buffer this.buffer
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @return the element at the offset
+     */
+    @SuppressWarnings("unchecked")
+    protected static final <E> E lpElement(E[] buffer, long offset) {
+        return (E) PlatformDependent0.UNSAFE.getObject(buffer, offset);
+    }
+
+    /**
+     * A volatile load (load + LoadLoad barrier) of an element from a given offset.
+     *
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @return the element at the offset
+     */
+    protected final E lvElement(long offset) {
+        return lvElement(buffer, offset);
+    }
+
+    /**
+     * A volatile load (load + LoadLoad barrier) of an element from a given offset.
+     *
+     * @param buffer this.buffer
+     * @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
+     * @return the element at the offset
+     */
+    @SuppressWarnings("unchecked")
+    protected static final <E> E lvElement(E[] buffer, long offset) {
+        return (E) PlatformDependent0.UNSAFE.getObjectVolatile(buffer, offset);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void clear() {
+        while (poll() != null || !isEmpty()) {
+            // looping
+        }
+    }
+
+    public int capacity() {
+        return (int) (mask + 1);
+    }
+}
+
+abstract class ConcurrentCircularArrayQueueL0Pad<E> extends AbstractQueue<E> {
+    long p00, p01, p02, p03, p04, p05, p06, p07;
+    long p30, p31, p32, p33, p34, p35, p36, p37;
+}
+

common/src/main/java/io/netty/util/internal/MpscArrayQueue.java

@@ -0,0 +1,331 @@
+/*
+ * Copyright 2015 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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.
+ */
+/*
+ * 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 io.netty.util.internal;
+
+/**
+ * Forked from <a href="https://github.com/JCTools/JCTools">JCTools</a>.
+ *
+ * A Multi-Producer-Single-Consumer queue based on a {@link ConcurrentCircularArrayQueue}. This implies that
+ * any thread may call the offer method, but only a single thread may call poll/peek for correctness to
+ * maintained. <br>
+ * This implementation follows patterns documented on the package level for False Sharing protection.<br>
+ * This implementation is using the <a href="http://sourceforge.net/projects/mc-fastflow/">Fast Flow</a>
+ * method for polling from the queue (with minor change to correctly publish the index) and an extension of
+ * the Leslie Lamport concurrent queue algorithm (originated by Martin Thompson) on the producer side.<br>
+ *
+ * @param <E>
+ */
+final class MpscArrayQueue<E> extends MpscArrayQueueConsumerField<E> {
+    long p40, p41, p42, p43, p44, p45, p46;
+    long p30, p31, p32, p33, p34, p35, p36, p37;
+
+    public MpscArrayQueue(final int capacity) {
+        super(capacity);
+    }
+
+    /**
+     * {@inheritDoc} <br>
+     *
+     * IMPLEMENTATION NOTES:<br>
+     * Lock free offer using a single CAS. As class name suggests access is permitted to many threads
+     * concurrently.
+     *
+     * @see java.util.Queue#offer(java.lang.Object)
+     */
+    @Override
+    public boolean offer(final E e) {
+        if (null == e) {
+            throw new NullPointerException("Null is not a valid element");
+        }
+
+        // use a cached view on consumer index (potentially updated in loop)
+        final long mask = this.mask;
+        final long capacity = mask + 1;
+        long consumerIndexCache = lvConsumerIndexCache(); // LoadLoad
+        long currentProducerIndex;
+        do {
+            currentProducerIndex = lvProducerIndex(); // LoadLoad
+            final long wrapPoint = currentProducerIndex - capacity;
+            if (consumerIndexCache <= wrapPoint) {
+                final long currHead = lvConsumerIndex(); // LoadLoad
+                if (currHead <= wrapPoint) {
+                    return false; // FULL :(
+                } else {
+                    // update shared cached value of the consumerIndex
+                    svConsumerIndexCache(currHead); // StoreLoad
+                    // update on stack copy, we might need this value again if we lose the CAS.
+                    consumerIndexCache = currHead;
+                }
+            }
+        } while (!casProducerIndex(currentProducerIndex, currentProducerIndex + 1));
+        /*
+         * NOTE: the new producer index value is made visible BEFORE the element in the array. If we relied on
+         * the index visibility to poll() we would need to handle the case where the element is not visible.
+         */
+
+        // Won CAS, move on to storing
+        final long offset = calcElementOffset(currentProducerIndex, mask);
+        soElement(offset, e); // StoreStore
+        return true; // AWESOME :)
+    }
+
+    /**
+     * A wait free alternative to offer which fails on CAS failure.
+     *
+     * @param e new element, not null
+     * @return 1 if next element cannot be filled, -1 if CAS failed, 0 if successful
+     */
+    public int weakOffer(final E e) {
+        if (null == e) {
+            throw new NullPointerException("Null is not a valid element");
+        }
+        final long mask = this.mask;
+        final long capacity = mask + 1;
+        final long currentTail = lvProducerIndex(); // LoadLoad
+        final long consumerIndexCache = lvConsumerIndexCache(); // LoadLoad
+        final long wrapPoint = currentTail - capacity;
+        if (consumerIndexCache <= wrapPoint) {
+            long currHead = lvConsumerIndex(); // LoadLoad
+            if (currHead <= wrapPoint) {
+                return 1; // FULL :(
+            } else {
+                svConsumerIndexCache(currHead); // StoreLoad
+            }
+        }
+
+        // look Ma, no loop!
+        if (!casProducerIndex(currentTail, currentTail + 1)) {
+            return -1; // CAS FAIL :(
+        }
+
+        // Won CAS, move on to storing
+        final long offset = calcElementOffset(currentTail, mask);
+        soElement(offset, e);
+        return 0; // AWESOME :)
+    }
+
+    /**
+     * {@inheritDoc}
+     * <p>
+     * IMPLEMENTATION NOTES:<br>
+     * Lock free poll using ordered loads/stores. As class name suggests access is limited to a single thread.
+     *
+     * @see java.util.Queue#poll()
+     */
+    @Override
+    public E poll() {
+        final long consumerIndex = lvConsumerIndex(); // LoadLoad
+        final long offset = calcElementOffset(consumerIndex);
+        // Copy field to avoid re-reading after volatile load
+        final E[] buffer = this.buffer;
+
+        // If we can't see the next available element we can't poll
+        E e = lvElement(buffer, offset); // LoadLoad
+        if (null == e) {
+            /*
+             * NOTE: Queue may not actually be empty in the case of a producer (P1) being interrupted after
+             * winning the CAS on offer but before storing the element in the queue. Other producers may go on
+             * to fill up the queue after this element.
+             */
+            if (consumerIndex != lvProducerIndex()) {
+                do {
+                    e = lvElement(buffer, offset);
+                } while (e == null);
+            } else {
+                return null;
+            }
+        }
+
+        spElement(buffer, offset, null);
+        soConsumerIndex(consumerIndex + 1); // StoreStore
+        return e;
+    }
+
+    /**
+     * {@inheritDoc}
+     * <p>
+     * IMPLEMENTATION NOTES:<br>
+     * Lock free peek using ordered loads. As class name suggests access is limited to a single thread.
+     *
+     * @see java.util.Queue#poll()
+     */
+    @Override
+    public E peek() {
+        // Copy field to avoid re-reading after volatile load
+        final E[] buffer = this.buffer;
+
+        final long consumerIndex = lvConsumerIndex(); // LoadLoad
+        final long offset = calcElementOffset(consumerIndex);
+        E e = lvElement(buffer, offset);
+        if (null == e) {
+            /*
+             * NOTE: Queue may not actually be empty in the case of a producer (P1) being interrupted after
+             * winning the CAS on offer but before storing the element in the queue. Other producers may go on
+             * to fill up the queue after this element.
+             */
+            if (consumerIndex != lvProducerIndex()) {
+                do {
+                    e = lvElement(buffer, offset);
+                } while (e == null);
+            } else {
+                return null;
+            }
+        }
+        return e;
+    }
+
+    /**
+     * {@inheritDoc}
+     * <p>
+     *
+     */
+    @Override
+    public int size() {
+        /*
+         * It is possible for a thread to be interrupted or reschedule between the read of the producer and
+         * consumer indices, therefore protection is required to ensure size is within valid range. In the
+         * event of concurrent polls/offers to this method the size is OVER estimated as we read consumer
+         * index BEFORE the producer index.
+         */
+        long after = lvConsumerIndex();
+        while (true) {
+            final long before = after;
+            final long currentProducerIndex = lvProducerIndex();
+            after = lvConsumerIndex();
+            if (before == after) {
+                return (int) (currentProducerIndex - after);
+            }
+        }
+    }
+
+    @Override
+    public boolean isEmpty() {
+        // Order matters!
+        // Loading consumer before producer allows for producer increments after consumer index is read.
+        // This ensures the correctness of this method at least for the consumer thread. Other threads POV is
+        // not really
+        // something we can fix here.
+        return lvConsumerIndex() == lvProducerIndex();
+    }
+}
+
+abstract class MpscArrayQueueL1Pad<E> extends ConcurrentCircularArrayQueue<E> {
+    long p10, p11, p12, p13, p14, p15, p16;
+    long p30, p31, p32, p33, p34, p35, p36, p37;
+
+    public MpscArrayQueueL1Pad(int capacity) {
+        super(capacity);
+    }
+}
+
+abstract class MpscArrayQueueTailField<E> extends MpscArrayQueueL1Pad<E> {
+    private static final long P_INDEX_OFFSET;
+
+    static {
+        try {
+            P_INDEX_OFFSET = PlatformDependent0.UNSAFE.objectFieldOffset(MpscArrayQueueTailField.class
+                                                                                 .getDeclaredField("producerIndex"));
+        } catch (NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+    }
+    private volatile long producerIndex;
+
+    public MpscArrayQueueTailField(int capacity) {
+        super(capacity);
+    }
+
+    protected final long lvProducerIndex() {
+        return producerIndex;
+    }
+
+    protected final boolean casProducerIndex(long expect, long newValue) {
+        return PlatformDependent0.UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
+    }
+}
+
+abstract class MpscArrayQueueMidPad<E> extends MpscArrayQueueTailField<E> {
+    long p20, p21, p22, p23, p24, p25, p26;
+    long p30, p31, p32, p33, p34, p35, p36, p37;
+
+    public MpscArrayQueueMidPad(int capacity) {
+        super(capacity);
+    }
+}
+
+abstract class MpscArrayQueueHeadCacheField<E> extends MpscArrayQueueMidPad<E> {
+    private volatile long headCache;
+
+    public MpscArrayQueueHeadCacheField(int capacity) {
+        super(capacity);
+    }
+
+    protected final long lvConsumerIndexCache() {
+        return headCache;
+    }
+
+    protected final void svConsumerIndexCache(long v) {
+        headCache = v;
+    }
+}
+
+abstract class MpscArrayQueueL2Pad<E> extends MpscArrayQueueHeadCacheField<E> {
+    long p20, p21, p22, p23, p24, p25, p26;
+    long p30, p31, p32, p33, p34, p35, p36, p37;
+
+    public MpscArrayQueueL2Pad(int capacity) {
+        super(capacity);
+    }
+}
+
+abstract class MpscArrayQueueConsumerField<E> extends MpscArrayQueueL2Pad<E> {
+    private static final long C_INDEX_OFFSET;
+    static {
+        try {
+            C_INDEX_OFFSET = PlatformDependent0.UNSAFE.objectFieldOffset(MpscArrayQueueConsumerField.class
+                                                                                 .getDeclaredField("consumerIndex"));
+        } catch (NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+    }
+    private volatile long consumerIndex;
+
+    public MpscArrayQueueConsumerField(int capacity) {
+        super(capacity);
+    }
+
+    protected final long lvConsumerIndex() {
+        return consumerIndex;
+    }
+
+    protected void soConsumerIndex(long l) {
+        PlatformDependent0.UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, l);
+    }
+}
+

common/src/main/java/io/netty/util/internal/PlatformDependent.java

@@ -40,6 +40,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedDeque;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.LinkedBlockingDeque;
+import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicLongFieldUpdater;
@@ -442,6 +443,18 @@ public final class PlatformDependent {
         return new MpscLinkedQueue<T>();
     }
 
+    /**
+     * Create a new {@link Queue} which is safe to use for multiple producers (different threads) and a single
+     * consumer (one thread!) with the given fixes {@code capacity}.
+     */
+    public static <T> Queue<T> newFixedMpscQueue(int capacity) {
+        if (hasUnsafe()) {
+            return new MpscArrayQueue<T>(capacity);
+        } else {
+            return new LinkedBlockingQueue<T>(capacity);
+        }
+    }
+
     /**
      * Return the {@link ClassLoader} for the given {@link Class}.
      */

common/src/main/java/io/netty/util/internal/PlatformDependent0.java

@@ -36,7 +36,7 @@ import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 final class PlatformDependent0 {
 
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(PlatformDependent0.class);
-    private static final Unsafe UNSAFE;
+    static final Unsafe UNSAFE;
     private static final boolean BIG_ENDIAN = ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN;
     private static final long ADDRESS_FIELD_OFFSET;
     private static final long ARRAY_BASE_OFFSET;

license/LICENSE.jctools.txt

@@ -0,0 +1,177 @@
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+                        http://www.apache.org/licenses/
+
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