[Java] Add RocksObject, the base class of all java objects with a c++ pointer.

Summary:
Add RocksObject, the base class of all java objects which has a c++ pointer.
While the finalizer of a RocksObject will release its c++ resource, it is
suggested to call its RocksObject.dispose() to manually release its
c++ resource.

Existing RocksDB java classes are now extending RocksObject.

Test Plan:
make rocksdbjava
make jtest
make jdb_bench

Reviewers: haobo, dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18411

java/RocksDBSample.java

@@ -218,7 +218,7 @@ public class RocksDBSample {
 
       System.out.println("iterator seek test passed.");
 
-      iterator.close();
+      iterator.dispose();
       System.out.println("iterator tests passed.");
 
       iterator = db.newIterator();
@@ -226,7 +226,7 @@ public class RocksDBSample {
       for (iterator.seekToLast(); iterator.isValid(); iterator.prev()) {
         keys.add(iterator.key());
       }
-      iterator.close();
+      iterator.dispose();
 
       Map<byte[], byte[]> values = db.multiGet(keys);
       assert(values.size() == keys.size());
@@ -248,5 +248,6 @@ public class RocksDBSample {
     // be sure to dispose c++ pointers
     options.dispose();
     readOptions.dispose();
+    filter.dispose();
   }
 }

java/org/rocksdb/BackupableDB.java

@@ -55,8 +55,8 @@ public class BackupableDB extends RocksDB {
    * should be transparent to Java developers.
    */
   @Override public synchronized void close() {
-    if (isOpened()) {
+    if (isInitialized()) {
-      super.close0();
+      super.close();
     }
   }
 
@@ -73,10 +73,6 @@ public class BackupableDB extends RocksDB {
     close();
   }
 
-  private boolean isOpened() {
-    return nativeHandle_ != 0;
-  }
-
   protected native void open(long rocksDBHandle, long backupDBOptionsHandle);
   protected native void createNewBackup(long handle, boolean flag);
 

java/org/rocksdb/BackupableDBOptions.java

@@ -12,8 +12,9 @@ package org.rocksdb;
  * Note that dispose() must be called before an Options instance
  * become out-of-scope to release the allocated memory in c++.
  */
-public class BackupableDBOptions {
+public class BackupableDBOptions extends RocksObject {
   public BackupableDBOptions(String path) {
+    super();
     newBackupableDBOptions(path);
   }
 
@@ -31,22 +32,13 @@ public class BackupableDBOptions {
    * Release the memory allocated for the current instance
    * in the c++ side.
    */
-  public synchronized void dispose() {
+  @Override public synchronized void dispose() {
     if (isInitialized()) {
       dispose(nativeHandle_);
     }
   }
 
-  @Override protected void finalize() {
-    dispose();
-  }
-
-  boolean isInitialized() {
-    return nativeHandle_ != 0;
-  }
-
   private native void newBackupableDBOptions(String path);
   private native String backupDir(long handle);
   private native void dispose(long handle);
-  long nativeHandle_;
 }

java/org/rocksdb/Filter.java

@@ -12,27 +12,21 @@ package org.rocksdb;
  * number of disk seeks form a handful to a single disk seek per
  * DB::Get() call.
  */
-public abstract class Filter {
+public abstract class Filter extends RocksObject {
-  protected long nativeHandle_ = 0;
-
   protected abstract void createNewFilter();
 
   /**
    * Deletes underlying C++ filter pointer.
+   *
+   * Note that this function should be called only after all
+   * RocksDB instances referencing the filter are closed.
+   * Otherwise an undefined behavior will occur.
    */
-  protected synchronized void dispose() {
+  @Override public synchronized void dispose() {
-    if(nativeHandle_ != 0) {
+    if (isInitialized()) {
       dispose0(nativeHandle_);
     }
   }
 
-  @Override protected void finalize() {
-    dispose();
-  }
-
-  protected boolean isInitialized() {
-    return (nativeHandle_ != 0);
-  }
-
   private native void dispose0(long handle);
 }

java/org/rocksdb/Iterator.java

@@ -16,10 +16,9 @@ package org.rocksdb;
  * non-const method, all threads accessing the same Iterator must use
  * external synchronization.
  */
-public class Iterator {
+public class Iterator extends RocksObject {
-  private long nativeHandle_;
-
   public Iterator(long nativeHandle) {
+    super();
     nativeHandle_ = nativeHandle;
   }
 
@@ -119,22 +118,15 @@ public class Iterator {
   /**
    * Deletes underlying C++ iterator pointer.
    */
-  public synchronized void close() {
+  @Override public synchronized void dispose() {
-    if(nativeHandle_ != 0) {
+    if(isInitialized()) {
-      close0(nativeHandle_);
+      dispose(nativeHandle_);
+      nativeHandle_ = 0;
     }
   }
 
-  @Override protected void finalize() {
-    close();
-  }
-
-  private boolean isInitialized() {
-    return (nativeHandle_ != 0);
-  }
-
   private native boolean isValid0(long handle);
-  private native void close0(long handle);
+  private native void dispose(long handle);
   private native void seekToFirst0(long handle);
   private native void seekToLast0(long handle);
   private native void next0(long handle);

java/org/rocksdb/Options.java

@@ -12,7 +12,7 @@ package org.rocksdb;
  * Note that dispose() must be called before an Options instance
  * become out-of-scope to release the allocated memory in c++.
  */
-public class Options {
+public class Options extends RocksObject {
   static final long DEFAULT_CACHE_SIZE = 8 << 20;
   /**
    * Construct options for opening a RocksDB.
@@ -21,7 +21,7 @@ public class Options {
    * an rocksdb::Options in the c++ side.
    */
   public Options() {
-    nativeHandle_ = 0;
+    super();
     cacheSize_ = DEFAULT_CACHE_SIZE;
     newOptions();
   }
@@ -2311,20 +2311,12 @@ public class Options {
    * Release the memory allocated for the current instance
    * in the c++ side.
    */
-  public synchronized void dispose() {
+  @Override public synchronized void dispose() {
     if (isInitialized()) {
       dispose0();
     }
   }
 
-  @Override protected void finalize() {
-    dispose();
-  }
-
-  private boolean isInitialized() {
-    return (nativeHandle_ != 0);
-  }
-
   static final int DEFAULT_PLAIN_TABLE_BLOOM_BITS_PER_KEY = 10;
   static final double DEFAULT_PLAIN_TABLE_HASH_TABLE_RATIO = 0.75;
   static final int DEFAULT_PLAIN_TABLE_INDEX_SPARSENESS = 16;
@@ -2358,7 +2350,6 @@ public class Options {
   private native void useFixedLengthPrefixExtractor(
       long handle, int prefixLength);
 
-  long nativeHandle_;
   long cacheSize_;
   Filter filter_;
 }

java/org/rocksdb/ReadOptions.java

@@ -11,9 +11,9 @@ package org.rocksdb;
  * Note that dispose() must be called before an Options instance
  * become out-of-scope to release the allocated memory in c++.
  */
-public class ReadOptions {
+public class ReadOptions extends RocksObject {
   public ReadOptions() {
-    nativeHandle_ = 0;
+    super();
     newReadOptions();
   }
   private native void newReadOptions();
@@ -24,7 +24,7 @@ public class ReadOptions {
    *
    * Calling other methods after dispose() leads to undefined behavior.
    */
-  public synchronized void dispose() {
+  @Override public synchronized void dispose() {
     if (isInitialized()) {
       dispose(nativeHandle_);
     }
@@ -127,10 +127,4 @@ public class ReadOptions {
   }
   private native void setTailing(
       long handle, boolean tailing);
-
-  protected long nativeHandle_;
-
-  private boolean isInitialized() {
-    return nativeHandle_ != 0;
-  }
 }

java/org/rocksdb/RocksDB.java

@@ -18,7 +18,7 @@ import org.rocksdb.util.Environment;
  * All methods of this class could potentially throw RocksDBException, which
  * indicates sth wrong at the rocksdb library side and the call failed.
  */
-public class RocksDB {
+public class RocksDB extends RocksObject {
   public static final int NOT_FOUND = -1;
   private static final String[] compressionLibs_ = {
       "snappy", "zlib", "bzip2", "lz4", "lz4hc"};
@@ -114,12 +114,21 @@ public class RocksDB {
     return db;
   }
 
-  public synchronized void close() {
+  @Override public synchronized void dispose() {
-    if (nativeHandle_ != 0) {
+    if (isInitialized()) {
-      close0();
+      dispose(nativeHandle_);
+      nativeHandle_ = 0;
     }
   }
 
+  /**
+   * Close the RocksDB instance.
+   * This function is equivalent to dispose().
+   */
+  public void close() {
+    dispose();
+  }
+
   /**
    * Set the database entry for "key" to "value".
    *
@@ -314,7 +323,7 @@ public class RocksDB {
    * Private constructor.
    */
   protected RocksDB() {
-    nativeHandle_ = 0;
+    super();
   }
 
   /**
@@ -361,8 +370,7 @@ public class RocksDB {
       long handle, long writeOptHandle,
       byte[] key, int keyLen) throws RocksDBException;
   protected native long iterator0(long optHandle);
-  protected native void close0();
+  protected native void dispose(long handle);
 
-  protected long nativeHandle_;
   protected Filter filter_;
 }

java/org/rocksdb/RocksObject.java

@@ -0,0 +1,35 @@
+// Copyright (c) 2014, Facebook, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+
+package org.rocksdb;
+
+/**
+ * RocksObject is the base-class of all RocksDB related class that has
+ * a pointer to some c++ rocksdb object.  Although RocksObject
+ * will release its c++ resource on its finalize() once it has been
+ * garbage-collected, it is suggested to call dispose() manually to
+ * release its c++ resource once an instance of RocksObject is no
+ * longer used.
+ */
+public abstract class RocksObject {
+  protected RocksObject() {
+    nativeHandle_ = 0;
+  }
+
+  /**
+   * Release the c++ object pointed by the native handle.
+   */
+  public abstract void dispose();
+
+  protected boolean isInitialized() {
+    return (nativeHandle_ != 0);
+  }
+
+  @Override protected void finalize() {
+    dispose();
+  }
+
+  protected long nativeHandle_;
+}

java/org/rocksdb/WriteBatch.java

@@ -24,9 +24,9 @@ import java.util.*;
  * non-const method, all threads accessing the same WriteBatch must use
  * external synchronization.
  */
-public class WriteBatch {
+public class WriteBatch extends RocksObject {
   public WriteBatch() {
-    nativeHandle_ = 0;
+    super();
     newWriteBatch(0);
   }
 
@@ -86,16 +86,12 @@ public class WriteBatch {
   /**
    * Delete the c++ side pointer.
    */
-  public synchronized void dispose() {
+  @Override public synchronized void dispose() {
-    if (nativeHandle_ != 0) {
+    if (isInitialized()) {
       dispose0();
     }
   }
 
-  @Override protected void finalize() {
-    dispose();
-  }
-
   private native void newWriteBatch(int reserved_bytes);
   private native void put(byte[] key, int keyLen,
                           byte[] value, int valueLen);
@@ -104,8 +100,6 @@ public class WriteBatch {
   private native void remove(byte[] key, int keyLen);
   private native void putLogData(byte[] blob, int blobLen);
   private native void dispose0();
-
-  long nativeHandle_;
 }
 
 /**

java/org/rocksdb/WriteOptions.java

@@ -11,14 +11,14 @@ package org.rocksdb;
  * Note that developers should call WriteOptions.dispose() to release the
  * c++ side memory before a WriteOptions instance runs out of scope.
  */
-public class WriteOptions {
+public class WriteOptions extends RocksObject {
   public WriteOptions() {
-    nativeHandle_ = 0;
+    super();
     newWriteOptions();
   }
 
-  public synchronized void dispose() {
+  @Override public synchronized void dispose() {
-    if (nativeHandle_ != 0) {
+    if (isInitialized()) {
       dispose0(nativeHandle_);
     }
   }
@@ -91,16 +91,10 @@ public class WriteOptions {
     return disableWAL(nativeHandle_);
   }
 
-  @Override protected void finalize() {
-    dispose();
-  }
-
   private native void newWriteOptions();
   private native void setSync(long handle, boolean flag);
   private native boolean sync(long handle);
   private native void setDisableWAL(long handle, boolean flag);
   private native boolean disableWAL(long handle);
   private native void dispose0(long handle);
-
-  protected long nativeHandle_;
 }

java/rocksjni/iterator.cc

@@ -26,7 +26,7 @@ jboolean Java_org_rocksdb_Iterator_isValid0(
 
 /*
  * Class:     org_rocksdb_Iterator
- * Method:    close0
+ * Method:    seekToFirst0
  * Signature: (J)V
  */
 void Java_org_rocksdb_Iterator_seekToFirst0(
@@ -135,13 +135,11 @@ void Java_org_rocksdb_Iterator_status0(
 
 /*
  * Class:     org_rocksdb_Iterator
- * Method:    status0
+ * Method:    dispose
  * Signature: (J)V
  */
-void Java_org_rocksdb_Iterator_close0(
+void Java_org_rocksdb_Iterator_dispose(
     JNIEnv* env, jobject jobj, jlong handle) {
   auto it = reinterpret_cast<rocksdb::Iterator*>(handle);
   delete it;
-
-  rocksdb::IteratorJni::setHandle(env, jobj, nullptr);
 }

java/rocksjni/rocksjni.cc

@@ -415,16 +415,14 @@ void Java_org_rocksdb_RocksDB_remove__JJ_3BI(
 
 /*
  * Class:     org_rocksdb_RocksDB
- * Method:    close0
+ * Method:    dispose
- * Signature: ()V
+ * Signature: (J)V
  */
-void Java_org_rocksdb_RocksDB_close0(
+void Java_org_rocksdb_RocksDB_dispose(
-    JNIEnv* env, jobject java_db) {
+    JNIEnv* env, jobject java_db, jlong jhandle) {
-  rocksdb::DB* db = rocksdb::RocksDBJni::getHandle(env, java_db);
+  auto db = reinterpret_cast<rocksdb::DB*>(jhandle);
   assert(db != nullptr);
   delete db;
-
-  rocksdb::RocksDBJni::setHandle(env, java_db, nullptr);
 }
 
 /*