Merge pull request #153 from bpot/fix_jni_segfault

Segfault when using BackupableDB with Java bindings

java/org/rocksdb/BackupableDB.java

@@ -25,11 +25,14 @@ public class BackupableDB extends RocksDB {
   public static BackupableDB open(
       Options opt, BackupableDBOptions bopt, String db_path)
       throws RocksDBException {
-    // since BackupableDB c++ will handle the life cycle of
-    // the returned RocksDB of RocksDB.open(), here we store
-    // it as a BackupableDB member variable to avoid GC.
-    BackupableDB bdb = new BackupableDB(RocksDB.open(opt, db_path));
-    bdb.open(bdb.db_.nativeHandle_, bopt.nativeHandle_);
+
+    RocksDB db = RocksDB.open(opt, db_path);
+    BackupableDB bdb = new BackupableDB();
+    bdb.open(db.nativeHandle_, bopt.nativeHandle_);
+
+    // Prevent the RocksDB object from attempting to delete
+    // the underly C++ DB object.
+    db.disOwnNativeObject();
 
     return bdb;
   }
@@ -64,9 +67,8 @@ public class BackupableDB extends RocksDB {
    * A protected construction that will be used in the static factory
    * method BackupableDB.open().
    */
-  protected BackupableDB(RocksDB db) {
+  protected BackupableDB() {
     super();
-    db_ = db;
   }
 
   @Override protected void finalize() {
@@ -75,6 +77,4 @@ public class BackupableDB extends RocksDB {
 
   protected native void open(long rocksDBHandle, long backupDBOptionsHandle);
   protected native void createNewBackup(long handle, boolean flag);
-
-  private final RocksDB db_;
 }

java/org/rocksdb/RocksDB.java

@@ -337,6 +337,18 @@ public class RocksDB extends RocksObject {
     opt.filter_ = null;
   }
 
+  /**
+   * Revoke ownership of the native object.
+   *
+   * This will prevent the object from attempting to delete the underlying
+   * native object in its finalizer. This must be used when another object
+   * (e.g. BackupableDB) takes over ownership of the native object or both
+   * will attempt to delete the underlying object when garbage collected.
+   */
+  protected void disOwnNativeObject() {
+    nativeHandle_ = 0;
+  }
+
   // native methods
   protected native void open(
       long optionsHandle, long cacheSize, String path) throws RocksDBException;