Index: CHANGES.txt
===================================================================
--- CHANGES.txt	(revision 885070)
+++ CHANGES.txt	(working copy)
@@ -23,6 +23,11 @@
   and equals methods, cause bad things to happen when caching
   BooleanQueries.  (Chris Hostetter, Mike McCandless)
 
+* LUCENE-2095: Fixes: when two threads call IndexWriter.commit() at
+  the same time, it's possible for commit to return control back to
+  one of the threads before all changes are actually committed.
+  (Sanne Grinovero via Mike McCandless)
+
 New features
 
 * LUCENE-2069: Added Unicode 4 support to LowerCaseFilter. Due to the switch
Index: src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 885070)
+++ src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -30,6 +30,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Random;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.analysis.Analyzer;
@@ -4610,4 +4611,56 @@
     _TestUtil.checkIndex(dir);
     dir.close();
   }
+
+  // LUCENE-2095: make sure with multiple threads commit
+  // doesn't return until all changes are in fact in the
+  // index
+  public void testCommitThreadSafety() throws Throwable {
+    final int NUM_THREADS = 5;
+    final double RUN_SEC = 0.5;
+    final Directory dir = new MockRAMDirectory();
+    final IndexWriter w = new IndexWriter(dir, new SimpleAnalyzer(), IndexWriter.MaxFieldLength.UNLIMITED);
+    w.commit();
+    final AtomicBoolean failed = new AtomicBoolean();
+    Thread[] threads = new Thread[NUM_THREADS];
+    final long endTime = System.currentTimeMillis()+((long) (RUN_SEC*1000));
+    for(int i=0;i<NUM_THREADS;i++) {
+      final int finalI = i;
+      threads[i] = new Thread() {
+          public void run() {
+            try {
+              final Document doc = new Document();
+              IndexReader r = IndexReader.open(dir);
+              Field f = new Field("f", "", Field.Store.NO, Field.Index.NOT_ANALYZED);
+              doc.add(f);
+              int count = 0;
+              while(System.currentTimeMillis() < endTime && !failed.get()) {
+                for(int j=0;j<10;j++) {
+                  final String s = finalI + "_" + String.valueOf(count++);
+                  f.setValue(s);
+                  w.addDocument(doc);
+                  w.commit();
+                  IndexReader r2 = r.reopen();
+                  assertTrue(r2 != r);
+                  r.close();
+                  r = r2;
+                  assertEquals("term=f:" + s, 1, r.docFreq(new Term("f", s)));
+                }
+              }
+              r.close();
+            } catch (Throwable t) {
+              failed.set(true);
+              throw new RuntimeException(t);
+            }
+          }
+        };
+      threads[i].start();
+    }
+    for(int i=0;i<NUM_THREADS;i++) {
+      threads[i].join();
+    }
+    w.close();
+    dir.close();
+    assertFalse(failed.get());
+  }
 }
Index: src/test/org/apache/lucene/store/TestRAMDirectory.java
===================================================================
--- src/test/org/apache/lucene/store/TestRAMDirectory.java	(revision 885070)
+++ src/test/org/apache/lucene/store/TestRAMDirectory.java	(working copy)
@@ -97,7 +97,7 @@
     searcher.close();
   }
   
-  private final int numThreads = 50;
+  private final int numThreads = 10;
   private final int docsPerThread = 40;
   
   public void testRAMDirectorySize() throws IOException, InterruptedException {
@@ -125,9 +125,6 @@
             } catch (IOException e) {
               throw new RuntimeException(e);
             }
-            synchronized (ramDir) {
-              assertEquals(ramDir.sizeInBytes(), ramDir.getRecomputedSizeInBytes());
-            }
           }
         }
       };
Index: src/test/org/apache/lucene/store/MockRAMDirectory.java
===================================================================
--- src/test/org/apache/lucene/store/MockRAMDirectory.java	(revision 885070)
+++ src/test/org/apache/lucene/store/MockRAMDirectory.java	(working copy)
@@ -18,7 +18,6 @@
  */
 
 import java.io.IOException;
-import java.io.File;
 import java.io.FileNotFoundException;
 import java.util.Iterator;
 import java.util.Random;
@@ -213,7 +212,7 @@
       throw new IOException("file " + name + " already exists");
     else {
       if (existing!=null) {
-        sizeInBytes -= existing.sizeInBytes;
+        sizeInBytes.getAndAdd(-existing.sizeInBytes);
         existing.directory = null;
       }
 
Index: src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- src/java/org/apache/lucene/index/IndexWriter.java	(revision 885070)
+++ src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -3378,9 +3378,14 @@
     startCommit(0, commitUserData);
   }
 
+  // Used only by commit, below; lock order is commitLock -> IW
+  private final Object commitLock = new Object();
+
   private void commit(long sizeInBytes) throws IOException {
-    startCommit(sizeInBytes, null);
-    finishCommit();
+    synchronized(commitLock) {
+      startCommit(sizeInBytes, null);
+      finishCommit();
+    }
   }
 
   /**
@@ -3430,17 +3435,26 @@
 
     ensureOpen();
 
-    if (infoStream != null)
+    if (infoStream != null) {
       message("commit: start");
+    }
 
-    if (pendingCommit == null) {
-      if (infoStream != null)
-        message("commit: now prepare");
-      prepareCommit(commitUserData);
-    } else if (infoStream != null)
-      message("commit: already prepared");
+    synchronized(commitLock) {
+      if (infoStream != null) {
+        message("commit: enter lock");
+      }
 
-    finishCommit();
+      if (pendingCommit == null) {
+        if (infoStream != null) {
+          message("commit: now prepare");
+        }
+        prepareCommit(commitUserData);
+      } else if (infoStream != null) {
+        message("commit: already prepared");
+      }
+
+      finishCommit();
+    }
   }
 
   private synchronized final void finishCommit() throws CorruptIndexException, IOException {
@@ -4554,6 +4568,9 @@
 
     assert testPoint("startStartCommit");
 
+    // TODO: as of LUCENE-2095, we can simplify this method,
+    // since only 1 thread can be in here at once
+
     if (hitOOM) {
       throw new IllegalStateException("this writer hit an OutOfMemoryError; cannot commit");
     }
Index: src/java/org/apache/lucene/store/RAMFile.java
===================================================================
--- src/java/org/apache/lucene/store/RAMFile.java	(revision 885070)
+++ src/java/org/apache/lucene/store/RAMFile.java	(working copy)
@@ -27,7 +27,7 @@
   private ArrayList<byte[]> buffers = new ArrayList<byte[]>();
   long length;
   RAMDirectory directory;
-  long sizeInBytes;                  // Only maintained if in a directory; updates synchronized on directory
+  long sizeInBytes;
 
   // This is publicly modifiable via Directory.touchFile(), so direct access not supported
   private long lastModified = System.currentTimeMillis();
@@ -57,16 +57,16 @@
     this.lastModified = lastModified;
   }
 
-  final synchronized byte[] addBuffer(int size) {
+  final byte[] addBuffer(int size) {
     byte[] buffer = newBuffer(size);
-    if (directory!=null)
-      synchronized (directory) {             // Ensure addition of buffer and adjustment to directory size are atomic wrt directory
-        buffers.add(buffer);
-        directory.sizeInBytes += size;
-        sizeInBytes += size;
-      }
-    else
+    synchronized(this) {
       buffers.add(buffer);
+      sizeInBytes += size;
+    }
+
+    if (directory != null) {
+      directory.sizeInBytes.getAndAdd(size);
+    }
     return buffer;
   }
 
@@ -88,11 +88,8 @@
     return new byte[size];
   }
 
-  // Only valid if in a directory
-  long getSizeInBytes() {
-    synchronized (directory) {
-      return sizeInBytes;
-    }
+  synchronized long getSizeInBytes() {
+    return sizeInBytes;
   }
   
 }
Index: src/java/org/apache/lucene/store/RAMDirectory.java
===================================================================
--- src/java/org/apache/lucene/store/RAMDirectory.java	(revision 885070)
+++ src/java/org/apache/lucene/store/RAMDirectory.java	(working copy)
@@ -22,6 +22,7 @@
 import java.io.Serializable;
 import java.util.HashMap;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicLong;
 import org.apache.lucene.util.ThreadInterruptedException;
 
 /**
@@ -34,7 +35,7 @@
   private static final long serialVersionUID = 1l;
 
   HashMap<String,RAMFile> fileMap = new HashMap<String,RAMFile>();
-  long sizeInBytes = 0;
+  final AtomicLong sizeInBytes = new AtomicLong();
   
   // *****
   // Lock acquisition sequence:  RAMDirectory, then RAMFile
@@ -153,7 +154,7 @@
    * RAMOutputStream.BUFFER_SIZE. */
   public synchronized final long sizeInBytes() {
     ensureOpen();
-    return sizeInBytes;
+    return sizeInBytes.get();
   }
   
   /** Removes an existing file in the directory.
@@ -166,7 +167,7 @@
     if (file!=null) {
         fileMap.remove(name);
         file.directory = null;
-        sizeInBytes -= file.sizeInBytes;       // updates to RAMFile.sizeInBytes synchronized on directory
+        sizeInBytes.addAndGet(-file.sizeInBytes);
     } else
       throw new FileNotFoundException(name);
   }
@@ -179,7 +180,7 @@
     synchronized (this) {
       RAMFile existing = fileMap.get(name);
       if (existing!=null) {
-        sizeInBytes -= existing.sizeInBytes;
+        sizeInBytes.addAndGet(existing.sizeInBytes);
         existing.directory = null;
       }
       fileMap.put(name, file);
Index: tags/lucene_3_0_back_compat_tests_20091125/src/test/org/apache/lucene/store/MockRAMDirectory.java
===================================================================
--- tags/lucene_3_0_back_compat_tests_20091125/src/test/org/apache/lucene/store/MockRAMDirectory.java	(revision 885078)
+++ tags/lucene_3_0_back_compat_tests_20091125/src/test/org/apache/lucene/store/MockRAMDirectory.java	(working copy)
@@ -213,7 +213,7 @@
       throw new IOException("file " + name + " already exists");
     else {
       if (existing!=null) {
-        sizeInBytes -= existing.sizeInBytes;
+        sizeInBytes.getAndAdd(-existing.sizeInBytes);
         existing.directory = null;
       }