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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
// This file implements the callback "bridge" between Java and C++ for
// rocksdb::Comparator and rocksdb::DirectComparator.
#include <jni.h>
#include <string>
#include "rocksdb/comparator.h"
#include "rocksdb/slice.h"
#include "port/port.h"
namespace rocksdb {
struct ComparatorJniCallbackOptions {
// Use adaptive mutex, which spins in the user space before resorting
// to kernel. This could reduce context switch when the mutex is not
// heavily contended. However, if the mutex is hot, we could end up
// wasting spin time.
// Default: false
bool use_adaptive_mutex;
ComparatorJniCallbackOptions() : use_adaptive_mutex(false) {
* This class acts as a bridge between C++
* and Java. The methods in this class will be
* called back from the RocksDB storage engine (C++)
* we then callback to the appropriate Java method
* this enables Comparators to be implemented in Java.
* The design of this Comparator caches the Java Slice
* objects that are used in the compare and findShortestSeparator
* method callbacks. Instead of creating new objects for each callback
* of those functions, by reuse via setHandle we are a lot
* faster; Unfortunately this means that we have to
* introduce independent locking in regions of each of those methods
* via the mutexs mtx_compare and mtx_findShortestSeparator respectively
class BaseComparatorJniCallback : public Comparator {
JNIEnv* env, jobject jComparator,
const ComparatorJniCallbackOptions* copt);
virtual ~BaseComparatorJniCallback();
virtual const char* Name() const;
virtual int Compare(const Slice& a, const Slice& b) const;
virtual void FindShortestSeparator(
std::string* start, const Slice& limit) const;
virtual void FindShortSuccessor(std::string* key) const;
// used for synchronisation in compare method
port::Mutex* mtx_compare;
// used for synchronisation in findShortestSeparator method
port::Mutex* mtx_findShortestSeparator;
jobject m_jComparator;
std::string m_name;
jmethodID m_jCompareMethodId;
jmethodID m_jFindShortestSeparatorMethodId;
jmethodID m_jFindShortSuccessorMethodId;
JavaVM* m_jvm;
jobject m_jSliceA;
jobject m_jSliceB;
jobject m_jSliceLimit;
class ComparatorJniCallback : public BaseComparatorJniCallback {
JNIEnv* env, jobject jComparator,
const ComparatorJniCallbackOptions* copt);
class DirectComparatorJniCallback : public BaseComparatorJniCallback {
JNIEnv* env, jobject jComparator,
const ComparatorJniCallbackOptions* copt);
} // namespace rocksdb