[jira] [Commented] (GEODE-6830) offheap FreeListManager has synchronization that hurts multi-threaded access

[Darrel Schneider (JIRA)]

    [ 
https://issues.apache.org/jira/browse/GEODE-6830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16856825#comment-16856825
 ] 

Darrel Schneider commented on GEODE-6830:
-----------------------------------------

Here are changes that remove the synchronization from the 
OffHeapStoredObjectAddressStack:
{noformat}
diff --git 
a/geode-core/src/main/java/org/apache/geode/internal/offheap/OffHeapStoredObjectAddressStack.java
 
b/geode-core/src/main/java/org/apache/geode/internal/offheap/OffHeapStoredObjectAddressStack.java
index a2174dc68b..72dfc65139 100644
--- 
a/geode-core/src/main/java/org/apache/geode/internal/offheap/OffHeapStoredObjectAddressStack.java
+++ 
b/geode-core/src/main/java/org/apache/geode/internal/offheap/OffHeapStoredObjectAddressStack.java
@@ -14,6 +14,8 @@
  */
 package org.apache.geode.internal.offheap;
 
+import java.util.concurrent.atomic.AtomicLongFieldUpdater;
+
 import org.apache.logging.log4j.Logger;
 
 import org.apache.geode.internal.offheap.FreeListManager.LongStack;
@@ -24,6 +26,8 @@ import 
org.apache.geode.internal.offheap.FreeListManager.LongStack;
  * free-list of the FreeListManager. This class is thread safe.
  */
 public class OffHeapStoredObjectAddressStack implements LongStack {
+  private static final AtomicLongFieldUpdater<OffHeapStoredObjectAddressStack> 
topAddrUpdater =
+      AtomicLongFieldUpdater.newUpdater(OffHeapStoredObjectAddressStack.class, 
"topAddr");
   // Ok to read without sync but must be synced on write
   private volatile long topAddr;
 
@@ -44,21 +48,22 @@ public class OffHeapStoredObjectAddressStack implements 
LongStack {
   public void offer(long e) {
     assert e != 0;
     MemoryAllocatorImpl.validateAddress(e);
-    synchronized (this) {
-      OffHeapStoredObject.setNext(e, this.topAddr);
-      this.topAddr = e;
-    }
+    long currentTopAddr;
+    do {
+      currentTopAddr = this.topAddr;
+      OffHeapStoredObject.setNext(e, currentTopAddr);
+    } while (!topAddrUpdater.compareAndSet(this, currentTopAddr, e));
   }
 
   @Override
   public long poll() {
     long result;
-    synchronized (this) {
+    do {
       result = this.topAddr;
-      if (result != 0L) {
-        this.topAddr = OffHeapStoredObject.getNext(result);
+      if (result == 0L) {
+        break;
       }
-    }
+    } while (!topAddrUpdater.compareAndSet(this, result, 
OffHeapStoredObject.getNext(result)));
     return result;
   }
{noformat}


> offheap FreeListManager has synchronization that hurts multi-threaded access
> ----------------------------------------------------------------------------
>
>                 Key: GEODE-6830
>                 URL: https://issues.apache.org/jira/browse/GEODE-6830
>             Project: Geode
>          Issue Type: Improvement
>          Components: offheap
>            Reporter: Darrel Schneider
>            Priority: Major
>
> The FreeListManager has a bunch of free lists implemented by 
> OffHeapStoredObjectAddressStack. Every time address is added or removed from 
> this stack it does a synchronization. This shows up as a place that threads 
> are blocked when 32 of them are doing pr puts.
> It also shows that the AtomicReferenceArray is expensive and I believe that 
> the current implementation could use a normal java array instead.



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