[JAVA-279]: ObjectId could generate duplicate ids if used in different classloader

Author: agirbal

src/main/com/mongodb/DBCollection.java

@@ -203,7 +203,7 @@ public WriteResult remove( DBObject o )
      * @param ref query used to search
      * @param fields the fields of matching objects to return
      * @param numToSkip will not return the first <tt>numToSkip</tt> matches
-     * @param batchSize if positive, is the # of objects per batch sent back from the db.  all objects that match will be returned.  if batchSize < 0, its a hard limit, and only 1 batch will either batchSize or the # that fit in a batch
+     * @param batchSize  if positive, represents the size of each batch of objects retrieved. If negative, it limits the total number of objects retrieved.
      * @param options - see Bytes QUERYOPTION_*
      * @return the objects, if found
      * @dochub find
@@ -212,10 +212,11 @@ public WriteResult remove( DBObject o )
 
     /**
      * Finds an object.
+     * Calls {@link DBCollection#find(com.mongodb.DBObject, com.mongodb.DBObject, int, int)} and applies the query options
      * @param ref query used to search
      * @param fields the fields of matching objects to return
      * @param numToSkip will not return the first <tt>numToSkip</tt> matches
-     * @param batchSize if positive, is the # of objects per batch sent back from the db.  all objects that match will be returned.  if batchSize < 0, its a hard limit, and only 1 batch will either batchSize or the # that fit in a batch
+     * @param batchSize if positive, represents the size of each batch of objects retrieved. If negative, it limits the total number of objects retrieved.
      * @param options - see Bytes QUERYOPTION_*
      * @return the objects, if found
      * @throws MongoException
@@ -231,7 +232,7 @@ public final DBCursor find( DBObject ref , DBObject fields , int numToSkip , int
      * @param ref query used to search
      * @param fields the fields of matching objects to return
      * @param numToSkip will not return the first <tt>numToSkip</tt> matches
-     * @param batchSize if positive, is the # of objects per batch sent back from the db.  all objects that match will be returned.  if batchSize < 0, its a hard limit, and only 1 batch will either batchSize or the # that fit in a batch
+     * @param batchSize if positive, represents the size of each batch of objects retrieved. If negative, it limits the total number of objects retrieved.
      * @return the objects, if found
      * @dochub find
      */

src/main/com/mongodb/DBCursor.java

@@ -655,7 +655,7 @@ public String toString() {
             sb.append(", fields=").append(getKeysWanted());
         sb.append(", numIterated=").append(_num);
         if (_numWanted > 0)
-            sb.append(", numWanted=").append(_numWanted);
+            sb.append(", limit=").append(_numWanted);
         if (_skip > 0)
             sb.append(", skip=").append(_skip);
         return sb.toString();

src/main/org/bson/types/ObjectId.java

@@ -342,7 +342,7 @@ private static int _curtime(){
     static {
 
         try {
-            
+            // build a 2-byte machine piece based on NICs info
             final int machinePiece;
             {
                 StringBuilder sb = new StringBuilder();
@@ -354,17 +354,25 @@ private static int _curtime(){
                 machinePiece = sb.toString().hashCode() << 16;
                 LOGGER.fine( "machine piece post: " + Integer.toHexString( machinePiece ) );
             }
-            
+
+            // add a 2 byte process piece. It must represent not only the JVM but the class loader.
+            // Since static var belong to class loader there could be collisions otherwise
             final int processPiece;
             {
-                int temp = new java.util.Random().nextInt();
+                int processId = new java.util.Random().nextInt();
                 try {
-                    temp = java.lang.management.ManagementFactory.getRuntimeMXBean().getName().hashCode();
+                    processId = java.lang.management.ManagementFactory.getRuntimeMXBean().getName().hashCode();
                 }
                 catch ( Throwable t ){
                 }
-                temp = temp & 0xFFFF;
-                processPiece = temp;
+
+                ClassLoader loader = ObjectId.class.getClassLoader();
+                int loaderId = loader != null ? System.identityHashCode(loader) : 0;
+
+                StringBuilder sb = new StringBuilder();
+                sb.append(Integer.toHexString(processId));
+                sb.append(Integer.toHexString(loaderId));
+                processPiece = sb.toString().hashCode() & 0xFFFF;
                 LOGGER.fine( "process piece: " + Integer.toHexString( processPiece ) );
             }