svn commit: r1503322 - /jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java

[jukka]

Author: jukka
Date: Mon Jul 15 16:32:58 2013
New Revision: 1503322

URL: http://svn.apache.org/r1503322
Log:
OAK-786: Fall back to pessimism

Add initial pessimistic merge algorithm, not yet enabled

Modified:
    
jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java

Modified: 
jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java
URL: 
http://svn.apache.org/viewvc/jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java?rev=1503322&r1=1503321&r2=1503322&view=diff
==============================================================================
--- 
jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java
 (original)
+++ 
jackrabbit/oak/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStoreBranch.java
 Mon Jul 15 16:32:58 2013
@@ -19,6 +19,7 @@ package org.apache.jackrabbit.oak.plugin
 import static org.apache.jackrabbit.oak.plugins.segment.SegmentNodeStore.ROOT;
 
 import java.util.Random;
+import java.util.UUID;
 
 import javax.annotation.Nonnull;
 
@@ -83,6 +84,54 @@ class SegmentNodeStoreBranch extends Abs
         }
     }
 
+    private synchronized NodeState pessimisticMerge(
+            CommitHook hook, long timeout) throws CommitFailedException {
+        while (true) {
+            SegmentNodeState before = store.getHead();
+            long now = System.currentTimeMillis();
+            if (before.hasProperty("token")
+                    && before.getLong("timeout") >= now) {
+                // locked by someone else, wait until unlocked or expired
+                // TODO: explicit sleep needed to avoid spinning?
+            } else {
+                // attempt to acquire the lock
+                NodeBuilder builder = before.builder();
+                builder.setProperty("token", UUID.randomUUID().toString());
+                builder.setProperty("timeout", now + timeout);
+
+                SegmentNodeState after =
+                        writer.writeNode(builder.getNodeState());
+                writer.flush();
+                if (store.setHead(before, after)) {
+                    SegmentNodeState originalBase = base;
+                    SegmentNodeState originalHead = head;
+
+                    // lock acquired; rebase, apply commit hooks, and unlock
+                    rebase();
+                    builder.setChildNode(ROOT, hook.processCommit(
+                            base.getChildNode(ROOT), head.getChildNode(ROOT)));
+                    builder.removeProperty("token");
+                    builder.removeProperty("timeout");
+
+                    // complete the commit
+                    SegmentNodeState newHead =
+                            writer.writeNode(builder.getNodeState());
+                    writer.flush();
+                    if (store.setHead(after, newHead)) {
+                        base = newHead;
+                        head = newHead;
+                        return getHead();
+                    } else {
+                        // something else happened, perhaps a timeout, so
+                        // undo the previous rebase and try again
+                        base = originalBase;
+                        head = originalHead;
+                    }
+                }
+            }
+        }
+    }
+
     @Override @Nonnull
     public synchronized NodeState merge(CommitHook hook)
             throws CommitFailedException {