LUCENE-6094: allow IW.rollback to stop CMS's stalling too

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1643508 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -358,6 +358,9 @@ Bug Fixes
 * LUCENE-5987: IndexWriter will now forcefully close itself on
   aborting exception (an exception that would otherwise cause silent
   data loss).  (Robert Muir, Mike McCandless)
+
+* LUCENE-6094: Allow IW.rollback to stop ConcurrentMergeScheduler even
+  when it's stalling because there are too many merges. (Mike McCandless)
   
 Documentation
 

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

@@ -300,8 +300,11 @@ public class ConcurrentMergeScheduler extends MergeScheduler {
   protected synchronized int mergeThreadCount() {
     int count = 0;
     for (MergeThread mt : mergeThreads) {
-      if (mt.isAlive() && mt.getCurrentMerge() != null) {
-        count++;
+      if (mt.isAlive()) {
+        MergePolicy.OneMerge merge = mt.getCurrentMerge();
+        if (merge != null && merge.isAborted() == false) {
+          count++;
+        }
       }
     }
     return count;
@@ -399,7 +402,8 @@ public class ConcurrentMergeScheduler extends MergeScheduler {
         message("    too many merges; stalling...");
       }
       try {
-        wait();
+        // Only wait 0.25 seconds, so if all merges are aborted (by IW.rollback) we notice:
+        wait(250);
       } catch (InterruptedException ie) {
         throw new ThreadInterruptedException(ie);
       }

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

@@ -209,8 +209,8 @@ public abstract class MergePolicy {
       while (paused) {
         try {
           // In theory we could wait() indefinitely, but we
-          // do 1000 msec, defensively
-          wait(1000);
+          // do 250 msec, defensively
+          wait(250);
         } catch (InterruptedException ie) {
           throw new RuntimeException(ie);
         }

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

@@ -482,4 +482,72 @@ public class TestConcurrentMergeScheduler extends LuceneTestCase {
     w.close();
     dir.close();
   }
+
+  // LUCENE-6094
+  public void testHangDuringRollback() throws Throwable {
+    Directory dir = newMockDirectory();
+    IndexWriterConfig iwc = new IndexWriterConfig(new MockAnalyzer(random()));
+    iwc.setMaxBufferedDocs(2);
+    LogDocMergePolicy mp = new LogDocMergePolicy();
+    iwc.setMergePolicy(mp);
+    mp.setMergeFactor(2);
+    final CountDownLatch mergeStart = new CountDownLatch(1);
+    final CountDownLatch mergeFinish = new CountDownLatch(1);
+    ConcurrentMergeScheduler cms = new ConcurrentMergeScheduler() {
+        @Override
+        protected void doMerge(MergePolicy.OneMerge merge) throws IOException {
+          mergeStart.countDown();
+          try {
+            mergeFinish.await();
+          } catch (InterruptedException ie) {
+            throw new RuntimeException(ie);
+          }
+          super.doMerge(merge);
+        }
+      };
+    cms.setMaxMergesAndThreads(1, 1);
+    iwc.setMergeScheduler(cms);
+
+    final IndexWriter w = new IndexWriter(dir, iwc);
+    
+    w.addDocument(new Document());
+    w.addDocument(new Document());
+    // flush
+
+    w.addDocument(new Document());
+    w.addDocument(new Document());
+    // flush + merge
+
+    // Wait for merge to kick off
+    mergeStart.await();
+
+    new Thread() {
+      @Override
+      public void run() {
+        try {
+          w.addDocument(new Document());
+          w.addDocument(new Document());
+          // flush
+
+          w.addDocument(new Document());
+          // W/o the fix for LUCENE-6094 we would hang forever here:
+          w.addDocument(new Document());
+          // flush + merge
+          
+          // Now allow first merge to finish:
+          mergeFinish.countDown();
+
+        } catch (Exception e) {
+          throw new RuntimeException(e);
+        }
+      }
+    }.start();
+
+    while (w.numDocs() != 8) {
+      Thread.sleep(10);
+    }
+
+    w.rollback();
+    dir.close();
+  }
 }