defensively switch to AtomicLong for IndexWriter's changeCount; make failing test a bit more evil

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1671258 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/index/IndexWriter.java

@@ -255,7 +255,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
   private final Directory mergeDirectory;  // used for merging
   private final Analyzer analyzer;    // how to analyze text
 
-  private volatile long changeCount; // increments every time a change is completed
+  private final AtomicLong changeCount = new AtomicLong(); // increments every time a change is completed
   private volatile long lastCommitChangeCount; // last changeCount that was committed
 
   private List<SegmentCommitInfo> rollbackSegments;      // list of segmentInfo we will fallback to if the commit fails
@@ -1526,7 +1526,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
       // could close, re-open and re-return the same segment
       // name that was previously returned which can cause
       // problems at least with ConcurrentMergeScheduler.
-      changeCount++;
+      changeCount.incrementAndGet();
       segmentInfos.changed();
       return "_" + Integer.toString(segmentInfos.counter++, Character.MAX_RADIX);
     }
@@ -1974,7 +1974,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
         deleter.checkpoint(segmentInfos, false);
         deleter.refresh();
 
-        lastCommitChangeCount = changeCount;
+        lastCommitChangeCount = changeCount.get();
         
         deleter.close();
 
@@ -2089,7 +2089,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
             // Don't bother saving any changes in our segmentInfos
             readerPool.dropAll(false);
             // Mark that the index has changed
-            ++changeCount;
+            changeCount.incrementAndGet();
             segmentInfos.changed();
             globalFieldNumberMap.clear();
 
@@ -2202,13 +2202,13 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
    *  close/commit we will write a new segments file, but
    *  does NOT bump segmentInfos.version. */
   synchronized void checkpointNoSIS() throws IOException {
-    changeCount++;
+    changeCount.incrementAndGet();
     deleter.checkpoint(segmentInfos, false);
   }
 
   /** Called internally if any index state has changed. */
   synchronized void changed() {
-    changeCount++;
+    changeCount.incrementAndGet();
     segmentInfos.changed();
   }
 
@@ -2712,7 +2712,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
               // sneak into the commit point:
               toCommit = segmentInfos.clone();
 
-              pendingCommitChangeCount = changeCount;
+              pendingCommitChangeCount = changeCount.get();
 
               // This protects the segmentInfos we are now going
               // to commit.  This is important in case, eg, while
@@ -2770,7 +2770,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
    */
   public final synchronized void setCommitData(Map<String,String> commitUserData) {
     segmentInfos.setUserData(new HashMap<>(commitUserData));
-    ++changeCount;
+    changeCount.incrementAndGet();
   }
   
   /**
@@ -2826,7 +2826,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
    *  merged finished, this method may return true right
    *  after you had just called {@link #commit}. */
   public final boolean hasUncommittedChanges() {
-    return changeCount != lastCommitChangeCount || docWriter.anyChanges() || bufferedUpdatesStream.any();
+    return changeCount.get() != lastCommitChangeCount || docWriter.anyChanges() || bufferedUpdatesStream.any();
   }
 
   private final void commitInternal(MergePolicy mergePolicy) throws IOException {
@@ -4253,7 +4253,7 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
 
       synchronized(this) {
 
-        if (lastCommitChangeCount > changeCount) {
+        if (lastCommitChangeCount > changeCount.get()) {
           throw new IllegalStateException("lastCommitChangeCount=" + lastCommitChangeCount + ",changeCount=" + changeCount);
         }
 

lucene/core/src/test/org/apache/lucene/index/TestSnapshotDeletionPolicy.java

@@ -22,6 +22,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Random;
+import java.util.concurrent.CountDownLatch;
 
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Document;
@@ -293,12 +294,14 @@ public class TestSnapshotDeletionPolicy extends LuceneTestCase {
 
     Thread[] threads = new Thread[10];
     final IndexCommit[] snapshots = new IndexCommit[threads.length];
+    final CountDownLatch startingGun = new CountDownLatch(1);
     for (int i = 0; i < threads.length; i++) {
       final int finalI = i;
       threads[i] = new Thread() {
         @Override
         public void run() {
           try {
+            startingGun.await();
             writer.addDocument(new Document());
             writer.commit();
             snapshots[finalI] = sdp.snapshot();
@@ -314,6 +317,8 @@ public class TestSnapshotDeletionPolicy extends LuceneTestCase {
       t.start();
     }
     
+    startingGun.countDown();
+
     for (Thread t : threads) {
       t.join();
     }