From 89da788fd23f3e745c799abb575a98696ebcdc2c Mon Sep 17 00:00:00 2001
From: Norman Maurer <norman_maurer@apple.com>
Date: Mon, 14 Mar 2016 09:09:24 +0100
Subject: [PATCH] Add proper synchronization when access metrics.

Motivation:

We also need to add synchronization when access fields to ensure we see the latest updates.

Modifications:

Add synchronization when read fields that are written concurrently.

Result:

Ensure correct visibility of updated.
---
 .../main/java/io/netty/buffer/PoolArena.java  | 33 ++++++++++++++-----
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/buffer/src/main/java/io/netty/buffer/PoolArena.java b/buffer/src/main/java/io/netty/buffer/PoolArena.java
index d8a546319d..3ff5eb6787 100644
--- a/buffer/src/main/java/io/netty/buffer/PoolArena.java
+++ b/buffer/src/main/java/io/netty/buffer/PoolArena.java
@@ -444,7 +444,11 @@ abstract class PoolArena<T> implements PoolArenaMetric {
 
     @Override
     public long numAllocations() {
-        return allocationsTiny.value() + allocationsSmall.value() + allocationsNormal + allocationsHuge.value();
+        final long allocsNormal;
+        synchronized (this) {
+            allocsNormal = allocationsNormal;
+        }
+        return allocationsTiny.value() + allocationsSmall.value() + allocsNormal + allocationsHuge.value();
     }
 
     @Override
@@ -458,27 +462,31 @@ abstract class PoolArena<T> implements PoolArenaMetric {
     }
 
     @Override
-    public long numNormalAllocations() {
+    public synchronized long numNormalAllocations() {
         return allocationsNormal;
     }
 
     @Override
     public long numDeallocations() {
-        return deallocationsTiny + deallocationsSmall + allocationsNormal + deallocationsHuge.value();
+        final long deallocs;
+        synchronized (this) {
+            deallocs = deallocationsTiny + deallocationsSmall + allocationsNormal;
+        }
+        return deallocs + deallocationsHuge.value();
     }
 
     @Override
-    public long numTinyDeallocations() {
+    public synchronized long numTinyDeallocations() {
         return deallocationsTiny;
     }
 
     @Override
-    public long numSmallDeallocations() {
+    public synchronized long numSmallDeallocations() {
         return deallocationsSmall;
     }
 
     @Override
-    public long numNormalDeallocations() {
+    public synchronized long numNormalDeallocations() {
         return deallocationsNormal;
     }
 
@@ -493,8 +501,12 @@ abstract class PoolArena<T> implements PoolArenaMetric {
     }
 
     @Override
-    public long numActiveAllocations() {
-        long val = numAllocations() - numDeallocations();
+    public  long numActiveAllocations() {
+        long val;
+        synchronized (this) {
+            val = allocationsNormal - deallocationsTiny - deallocationsSmall - allocationsNormal;
+        }
+        val -= deallocationsHuge.value();
         return val >= 0 ? val : 0;
     }
 
@@ -512,7 +524,10 @@ abstract class PoolArena<T> implements PoolArenaMetric {
 
     @Override
     public long numActiveNormalAllocations() {
-        long val = numNormalAllocations() - numNormalDeallocations();
+        final long val;
+        synchronized (this) {
+            val = allocationsNormal - deallocationsNormal;
+        }
         return val >= 0 ? val : 0;
     }