Cleanup PoolChunk and PoolArena

Motivation:

To make it easier to understand PoolChunk and PoolArena we should cleanup duplicated code.

Modifications:

- Move reused code into methods
- Use Math.max(...)

Result:

Cleaner code and easier to understand.

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

@@ -26,6 +26,8 @@ import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import static java.lang.Math.max;
+
 abstract class PoolArena<T> implements PoolArenaMetric {
     static final boolean HAS_UNSAFE = PlatformDependent.hasUnsafe();
 
@@ -506,19 +508,17 @@ abstract class PoolArena<T> implements PoolArenaMetric {
         synchronized (this) {
             val += allocationsNormal - (deallocationsTiny + deallocationsSmall + deallocationsNormal);
         }
-        return val >= 0 ? val : 0;
+        return max(val, 0);
     }
 
     @Override
     public long numActiveTinyAllocations() {
-        long val = numTinyAllocations() - numTinyDeallocations();
+        return max(numTinyAllocations() - numTinyDeallocations(), 0);
-        return val >= 0 ? val : 0;
     }
 
     @Override
     public long numActiveSmallAllocations() {
-        long val = numSmallAllocations() - numSmallDeallocations();
+        return max(numSmallAllocations() - numSmallDeallocations(), 0);
-        return val >= 0 ? val : 0;
     }
 
     @Override
@@ -527,13 +527,12 @@ abstract class PoolArena<T> implements PoolArenaMetric {
         synchronized (this) {
             val = allocationsNormal - deallocationsNormal;
         }
-        return val >= 0 ? val : 0;
+        return max(val, 0);
     }
 
     @Override
     public long numActiveHugeAllocations() {
-        long val = numHugeAllocations() - numHugeDeallocations();
+        return max(numHugeAllocations() - numHugeDeallocations(), 0);
-        return val >= 0 ? val : 0;
     }
 
     protected abstract PoolChunk<T> newChunk(int pageSize, int maxOrder, int pageShifts, int chunkSize);

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

@@ -102,6 +102,8 @@ package io.netty.buffer;
  */
 final class PoolChunk<T> implements PoolChunkMetric {
 
+    private static final int INTEGER_SIZE_MINUS_ONE = Integer.SIZE - 1;
+
     final PoolArena<T> arena;
     final T memory;
     final boolean unpooled;
@@ -342,8 +344,8 @@ final class PoolChunk<T> implements PoolChunkMetric {
      * @param handle handle to free
      */
     void free(long handle) {
-        int memoryMapIdx = (int) handle;
+        int memoryMapIdx = memoryMapIdx(handle);
-        int bitmapIdx = (int) (handle >>> Integer.SIZE);
+        int bitmapIdx = bitmapIdx(handle);
 
         if (bitmapIdx != 0) { // free a subpage
             PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
@@ -364,8 +366,8 @@ final class PoolChunk<T> implements PoolChunkMetric {
     }
 
     void initBuf(PooledByteBuf<T> buf, long handle, int reqCapacity) {
-        int memoryMapIdx = (int) handle;
+        int memoryMapIdx = memoryMapIdx(handle);
-        int bitmapIdx = (int) (handle >>> Integer.SIZE);
+        int bitmapIdx = bitmapIdx(handle);
         if (bitmapIdx == 0) {
             byte val = value(memoryMapIdx);
             assert val == unusable : String.valueOf(val);
@@ -377,13 +379,13 @@ final class PoolChunk<T> implements PoolChunkMetric {
     }
 
     void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int reqCapacity) {
-        initBufWithSubpage(buf, handle, (int) (handle >>> Integer.SIZE), reqCapacity);
+        initBufWithSubpage(buf, handle, bitmapIdx(handle), reqCapacity);
     }
 
     private void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int bitmapIdx, int reqCapacity) {
         assert bitmapIdx != 0;
 
-        int memoryMapIdx = (int) handle;
+        int memoryMapIdx = memoryMapIdx(handle);
 
         PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
         assert subpage.doNotDestroy;
@@ -409,7 +411,7 @@ final class PoolChunk<T> implements PoolChunkMetric {
 
     private static int log2(int val) {
         // compute the (0-based, with lsb = 0) position of highest set bit i.e, log2
-        return Integer.SIZE - 1 - Integer.numberOfLeadingZeros(val);
+        return INTEGER_SIZE_MINUS_ONE - Integer.numberOfLeadingZeros(val);
     }
 
     private int runLength(int id) {
@@ -427,6 +429,14 @@ final class PoolChunk<T> implements PoolChunkMetric {
         return memoryMapIdx ^ maxSubpageAllocs; // remove highest set bit, to get offset
     }
 
+    private static int memoryMapIdx(long handle) {
+        return (int) handle;
+    }
+
+    private static int bitmapIdx(long handle) {
+        return (int) (handle >>> Integer.SIZE);
+    }
+
     @Override
     public int chunkSize() {
         return chunkSize;