LUCENE-3705: IWFlushQueue deadlocks if deletes are flushed and a segment is published at the same time

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1233248 13f79535-47bb-0310-9956-ffa450edef68

lucene/src/java/org/apache/lucene/index/DocumentsWriterFlushQueue.java

@@ -34,19 +34,24 @@ public class DocumentsWriterFlushQueue {
   private final AtomicInteger ticketCount = new AtomicInteger();
   private final ReentrantLock purgeLock = new ReentrantLock();
 
-  synchronized void addDeletesAndPurge(DocumentsWriter writer,
+  void addDeletesAndPurge(DocumentsWriter writer,
       DocumentsWriterDeleteQueue deleteQueue) throws IOException {
+    synchronized (this) {
       incTickets();// first inc the ticket count - freeze opens
                    // a window for #anyChanges to fail
       boolean success = false;
       try {
-      queue.add(new GlobalDeletesTicket(deleteQueue.freezeGlobalBuffer(null)));
+        queue
+            .add(new GlobalDeletesTicket(deleteQueue.freezeGlobalBuffer(null)));
         success = true;
       } finally {
         if (!success) {
           decTickets();
         }
       }
+    }
+    // don't hold the lock on the FlushQueue when forcing the purge - this blocks and deadlocks 
+    // if we hold the lock.
     forcePurge(writer);
   }
   
@@ -127,6 +132,7 @@ public class DocumentsWriterFlushQueue {
   }
 
   void forcePurge(DocumentsWriter writer) throws IOException {
+    assert !Thread.holdsLock(this);
     purgeLock.lock();
     try {
       innerPurge(writer);
@@ -136,6 +142,7 @@ public class DocumentsWriterFlushQueue {
   }
 
   void tryPurge(DocumentsWriter writer) throws IOException {
+    assert !Thread.holdsLock(this);
     if (purgeLock.tryLock()) {
       try {
         innerPurge(writer);