[#3654] No need to hold lock while destroy a chunk

Motiviation:

At the moment we sometimes hold the lock on the PoolArena during destroy a PoolChunk. This is not needed.

Modification:

- Ensure we not hold the lock during destroy a PoolChunk
- Move all synchronized usage in PoolArena
- Cleanup

Result:

Less condition.

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

@@ -27,6 +27,12 @@ import java.util.List;
 
 abstract class PoolArena<T> implements PoolArenaMetric {
 
+    enum SizeClass {
+        Tiny,
+        Small,
+        Normal
+    }
+
     static final int numTinySubpagePools = 512 >>> 4;
 
     final PooledByteBufAllocator parent;
@@ -83,19 +89,19 @@ abstract class PoolArena<T> implements PoolArenaMetric {
             smallSubpagePools[i] = newSubpagePoolHead(pageSize);
         }
 
-        q100 = new PoolChunkList<T>(this, null, 100, Integer.MAX_VALUE);
+        q100 = new PoolChunkList<T>(null, 100, Integer.MAX_VALUE);
-        q075 = new PoolChunkList<T>(this, q100, 75, 100);
+        q075 = new PoolChunkList<T>(q100, 75, 100);
-        q050 = new PoolChunkList<T>(this, q075, 50, 100);
+        q050 = new PoolChunkList<T>(q075, 50, 100);
-        q025 = new PoolChunkList<T>(this, q050, 25, 75);
+        q025 = new PoolChunkList<T>(q050, 25, 75);
-        q000 = new PoolChunkList<T>(this, q025, 1, 50);
+        q000 = new PoolChunkList<T>(q025, 1, 50);
-        qInit = new PoolChunkList<T>(this, q000, Integer.MIN_VALUE, 25);
+        qInit = new PoolChunkList<T>(q000, Integer.MIN_VALUE, 25);
 
-        q100.prevList = q075;
+        q100.prevList(q075);
-        q075.prevList = q050;
+        q075.prevList(q050);
-        q050.prevList = q025;
+        q050.prevList(q025);
-        q025.prevList = q000;
+        q025.prevList(q000);
-        q000.prevList = null;
+        q000.prevList(null);
-        qInit.prevList = qInit;
+        qInit.prevList(qInit);
 
         List<PoolChunkListMetric> metrics = new ArrayList<PoolChunkListMetric>(6);
         metrics.add(qInit);
@@ -234,25 +240,46 @@ abstract class PoolArena<T> implements PoolArenaMetric {
             allocationsHuge.decrement();
             destroyChunk(chunk);
         } else {
+            SizeClass sizeClass = sizeClass(normCapacity);
             if (sameThreads) {
-                PoolThreadCache cache = parent.threadCache.get();
+                PoolThreadCache cache = parent.threadCache();
-                if (cache.add(this, chunk, handle, normCapacity)) {
+                if (cache.add(this, chunk, handle, normCapacity, sizeClass)) {
                     // cached so not free it.
                     return;
                 }
             }
+            freeChunk(chunk, handle, sizeClass);
+        }
+    }
 
-            boolean tinyOrSmall = isTinyOrSmall(normCapacity);
+    private SizeClass sizeClass(int normCapacity) {
-            synchronized (this) {
+        if (!isTinyOrSmall(normCapacity)) {
-                if (!tinyOrSmall) {
+            return SizeClass.Normal;
-                    ++deallocationsNormal;
+        }
-                } else if (isTiny(normCapacity)) {
+        return isTiny(normCapacity) ? SizeClass.Tiny : SizeClass.Small;
-                    ++deallocationsTiny;
+    }
-                } else {
+
-                    ++deallocationsSmall;
+    void freeChunk(PoolChunk<T> chunk, long handle, SizeClass sizeClass) {
-                }
+        final boolean destroyChunk;
-                chunk.parent.free(chunk, handle);
+        synchronized (this) {
+            switch (sizeClass) {
+            case Normal:
+                ++deallocationsNormal;
+                break;
+            case Small:
+                ++deallocationsSmall;
+                break;
+            case Tiny:
+                ++deallocationsTiny;
+                break;
+            default:
+                throw new Error();
             }
+            destroyChunk = !chunk.parent.free(chunk, handle);
+        }
+        if (destroyChunk) {
+            // destroyChunk not need to be called while holding the synchronized lock.
+            destroyChunk(chunk);
         }
     }
 
@@ -328,7 +355,7 @@ abstract class PoolArena<T> implements PoolArenaMetric {
         int readerIndex = buf.readerIndex();
         int writerIndex = buf.writerIndex();
 
-        allocate(parent.threadCache.get(), buf, newCapacity);
+        allocate(parent.threadCache(), buf, newCapacity);
         if (newCapacity > oldCapacity) {
             memoryCopy(
                     oldMemory, oldOffset,

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

@@ -25,25 +25,29 @@ import java.util.List;
 
 final class PoolChunkList<T> implements PoolChunkListMetric {
     private static final Iterator<PoolChunkMetric> EMPTY_METRICS = Collections.<PoolChunkMetric>emptyList().iterator();
-    private final PoolArena<T> arena;
     private final PoolChunkList<T> nextList;
-    PoolChunkList<T> prevList;
-
     private final int minUsage;
     private final int maxUsage;
 
     private PoolChunk<T> head;
 
+    // This is only update once when create the linked like list of PoolChunkList in PoolArena constructor.
+    private PoolChunkList<T> prevList;
+
     // TODO: Test if adding padding helps under contention
     //private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
 
-    PoolChunkList(PoolArena<T> arena, PoolChunkList<T> nextList, int minUsage, int maxUsage) {
+    PoolChunkList(PoolChunkList<T> nextList, int minUsage, int maxUsage) {
-        this.arena = arena;
         this.nextList = nextList;
         this.minUsage = minUsage;
         this.maxUsage = maxUsage;
     }
 
+    void prevList(PoolChunkList<T> prevList) {
+        assert this.prevList == null;
+        this.prevList = prevList;
+    }
+
     boolean allocate(PooledByteBuf<T> buf, int reqCapacity, int normCapacity) {
         if (head == null) {
             return false;
@@ -67,17 +71,19 @@ final class PoolChunkList<T> implements PoolChunkListMetric {
         }
     }
 
-    void free(PoolChunk<T> chunk, long handle) {
+    boolean free(PoolChunk<T> chunk, long handle) {
         chunk.free(handle);
         if (chunk.usage() < minUsage) {
             remove(chunk);
             if (prevList == null) {
                 assert chunk.usage() == 0;
-                arena.destroyChunk(chunk);
+                return false;
             } else {
                 prevList.add(chunk);
+                return true;
             }
         }
+        return true;
     }
 
     void add(PoolChunk<T> chunk) {

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

@@ -17,6 +17,7 @@
 package io.netty.buffer;
 
 
+import io.netty.buffer.PoolArena.SizeClass;
 import io.netty.util.ThreadDeathWatcher;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
@@ -77,8 +78,10 @@ final class PoolThreadCache {
         this.heapArena = heapArena;
         this.directArena = directArena;
         if (directArena != null) {
-            tinySubPageDirectCaches = createSubPageCaches(tinyCacheSize, PoolArena.numTinySubpagePools);
+            tinySubPageDirectCaches = createSubPageCaches(
-            smallSubPageDirectCaches = createSubPageCaches(smallCacheSize, directArena.numSmallSubpagePools);
+                    tinyCacheSize, PoolArena.numTinySubpagePools, SizeClass.Tiny);
+            smallSubPageDirectCaches = createSubPageCaches(
+                    smallCacheSize, directArena.numSmallSubpagePools, SizeClass.Small);
 
             numShiftsNormalDirect = log2(directArena.pageSize);
             normalDirectCaches = createNormalCaches(
@@ -92,8 +95,10 @@ final class PoolThreadCache {
         }
         if (heapArena != null) {
             // Create the caches for the heap allocations
-            tinySubPageHeapCaches = createSubPageCaches(tinyCacheSize, PoolArena.numTinySubpagePools);
+            tinySubPageHeapCaches = createSubPageCaches(
-            smallSubPageHeapCaches = createSubPageCaches(smallCacheSize, heapArena.numSmallSubpagePools);
+                    tinyCacheSize, PoolArena.numTinySubpagePools, SizeClass.Tiny);
+            smallSubPageHeapCaches = createSubPageCaches(
+                    smallCacheSize, heapArena.numSmallSubpagePools, SizeClass.Small);
 
             numShiftsNormalHeap = log2(heapArena.pageSize);
             normalHeapCaches = createNormalCaches(
@@ -111,13 +116,14 @@ final class PoolThreadCache {
         ThreadDeathWatcher.watch(thread, freeTask);
     }
 
-    private static <T> SubPageMemoryRegionCache<T>[] createSubPageCaches(int cacheSize, int numCaches) {
+    private static <T> SubPageMemoryRegionCache<T>[] createSubPageCaches(
+            int cacheSize, int numCaches, SizeClass sizeClass) {
         if (cacheSize > 0) {
             @SuppressWarnings("unchecked")
             SubPageMemoryRegionCache<T>[] cache = new SubPageMemoryRegionCache[numCaches];
             for (int i = 0; i < cache.length; i++) {
                 // TODO: maybe use cacheSize / cache.length
-                cache[i] = new SubPageMemoryRegionCache<T>(cacheSize);
+                cache[i] = new SubPageMemoryRegionCache<T>(cacheSize, sizeClass);
             }
             return cache;
         } else {
@@ -191,23 +197,27 @@ final class PoolThreadCache {
      * Returns {@code true} if it fit into the cache {@code false} otherwise.
      */
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    boolean add(PoolArena<?> area, PoolChunk chunk, long handle, int normCapacity) {
+    boolean add(PoolArena<?> area, PoolChunk chunk, long handle, int normCapacity, SizeClass sizeClass) {
-        MemoryRegionCache<?> cache;
+        MemoryRegionCache<?> cache = cache(area, normCapacity, sizeClass);
-        if (area.isTinyOrSmall(normCapacity)) {
-            if (PoolArena.isTiny(normCapacity)) {
-                cache = cacheForTiny(area, normCapacity);
-            } else {
-                cache = cacheForSmall(area, normCapacity);
-            }
-        } else {
-            cache = cacheForNormal(area, normCapacity);
-        }
         if (cache == null) {
             return false;
         }
         return cache.add(chunk, handle);
     }
 
+    private MemoryRegionCache<?> cache(PoolArena<?> area, int normCapacity, SizeClass sizeClass) {
+        switch (sizeClass) {
+        case Normal:
+            return cacheForNormal(area, normCapacity);
+        case Small:
+            return cacheForSmall(area, normCapacity);
+        case Tiny:
+            return cacheForTiny(area, normCapacity);
+        default:
+            throw new Error();
+        }
+    }
+
     /**
      *  Should be called if the Thread that uses this cache is about to exist to release resources out of the cache
      */
@@ -309,8 +319,8 @@ final class PoolThreadCache {
      * Cache used for buffers which are backed by TINY or SMALL size.
      */
     private static final class SubPageMemoryRegionCache<T> extends MemoryRegionCache<T> {
-        SubPageMemoryRegionCache(int size) {
+        SubPageMemoryRegionCache(int size, SizeClass sizeClass) {
-            super(size);
+            super(size, sizeClass);
         }
 
         @Override
@@ -325,7 +335,7 @@ final class PoolThreadCache {
      */
     private static final class NormalMemoryRegionCache<T> extends MemoryRegionCache<T> {
         NormalMemoryRegionCache(int size) {
-            super(size);
+            super(size, SizeClass.Normal);
         }
 
         @Override
@@ -343,6 +353,7 @@ final class PoolThreadCache {
      */
     private abstract static class MemoryRegionCache<T> {
         private final Entry<T>[] entries;
+        private final SizeClass sizeClass;
         private final int maxUnusedCached;
         private int head;
         private int tail;
@@ -350,12 +361,13 @@ final class PoolThreadCache {
         private int entriesInUse;
 
         @SuppressWarnings("unchecked")
-        MemoryRegionCache(int size) {
+        MemoryRegionCache(int size, SizeClass sizeClass) {
             entries = new Entry[powerOfTwo(size)];
             for (int i = 0; i < entries.length; i++) {
                 entries[i] = new Entry<T>();
             }
             maxUnusedCached = size / 2;
+            this.sizeClass = sizeClass;
         }
 
         private static int powerOfTwo(int res) {
@@ -460,15 +472,12 @@ final class PoolThreadCache {
         }
 
         @SuppressWarnings({ "unchecked", "rawtypes" })
-        private static boolean freeEntry(Entry entry) {
+        private boolean freeEntry(Entry entry) {
             PoolChunk chunk = entry.chunk;
             if (chunk == null) {
                 return false;
             }
-            // need to synchronize on the area from which it was allocated before.
+            chunk.arena.freeChunk(chunk, entry.handle, sizeClass);
-            synchronized (chunk.arena) {
-                chunk.parent.free(chunk, entry.handle);
-            }
             entry.chunk = null;
             return true;
         }

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

@@ -127,11 +127,9 @@ public class PooledByteBufAllocator extends AbstractByteBufAllocator {
     private final int tinyCacheSize;
     private final int smallCacheSize;
     private final int normalCacheSize;
-
     private final List<PoolArenaMetric> heapArenaMetrics;
     private final List<PoolArenaMetric> directArenaMetrics;
-
+    private final PoolThreadLocalCache threadCache;
-    final PoolThreadLocalCache threadCache;
 
     public PooledByteBufAllocator() {
         this(false);
@@ -379,6 +377,10 @@ public class PooledByteBufAllocator extends AbstractByteBufAllocator {
         return normalCacheSize;
     }
 
+    final PoolThreadCache threadCache() {
+        return threadCache.get();
+    }
+
     // Too noisy at the moment.
     //
     //public String toString() {