ceph/src/rocksdb/java/rocksjni/comparatorjnicallback.h

   1 // Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 // This source code is licensed under the BSD-style license found in the
   3 // LICENSE file in the root directory of this source tree. An additional grant
   4 // of patent rights can be found in the PATENTS file in the same directory.
   5 //
   6 // This file implements the callback "bridge" between Java and C++ for
   7 // rocksdb::Comparator and rocksdb::DirectComparator.
   8
   9 #ifndef JAVA_ROCKSJNI_COMPARATORJNICALLBACK_H_
  10 #define JAVA_ROCKSJNI_COMPARATORJNICALLBACK_H_
  11
  12 #include <jni.h>
  13 #include <string>
  14 #include "rocksdb/comparator.h"
  15 #include "rocksdb/slice.h"
  16 #include "port/port.h"
  17
  18 namespace rocksdb {
  19
  20 struct ComparatorJniCallbackOptions {
  21   // Use adaptive mutex, which spins in the user space before resorting
  22   // to kernel. This could reduce context switch when the mutex is not
  23   // heavily contended. However, if the mutex is hot, we could end up
  24   // wasting spin time.
  25   // Default: false
  26   bool use_adaptive_mutex;
  27
  28   ComparatorJniCallbackOptions() : use_adaptive_mutex(false) {
  29   }
  30 };
  31
  32 /**
  33  * This class acts as a bridge between C++
  34  * and Java. The methods in this class will be
  35  * called back from the RocksDB storage engine (C++)
  36  * we then callback to the appropriate Java method
  37  * this enables Comparators to be implemented in Java.
  38  *
  39  * The design of this Comparator caches the Java Slice
  40  * objects that are used in the compare and findShortestSeparator
  41  * method callbacks. Instead of creating new objects for each callback
  42  * of those functions, by reuse via setHandle we are a lot
  43  * faster; Unfortunately this means that we have to
  44  * introduce independent locking in regions of each of those methods
  45  * via the mutexs mtx_compare and mtx_findShortestSeparator respectively
  46  */
  47 class BaseComparatorJniCallback : public Comparator {
  48  public:
  49     BaseComparatorJniCallback(
  50       JNIEnv* env, jobject jComparator,
  51       const ComparatorJniCallbackOptions* copt);
  52     virtual ~BaseComparatorJniCallback();
  53     virtual const char* Name() const;
  54     virtual int Compare(const Slice& a, const Slice& b) const;
  55     virtual void FindShortestSeparator(
  56       std::string* start, const Slice& limit) const;
  57     virtual void FindShortSuccessor(std::string* key) const;
  58
  59  private:
  60     // used for synchronisation in compare method
  61     port::Mutex* mtx_compare;
  62     // used for synchronisation in findShortestSeparator method
  63     port::Mutex* mtx_findShortestSeparator;
  64     jobject m_jComparator;
  65     std::string m_name;
  66     jmethodID m_jCompareMethodId;
  67     jmethodID m_jFindShortestSeparatorMethodId;
  68     jmethodID m_jFindShortSuccessorMethodId;
  69
  70  protected:
  71     JavaVM* m_jvm;
  72     jobject m_jSliceA;
  73     jobject m_jSliceB;
  74     jobject m_jSliceLimit;
  75 };
  76
  77 class ComparatorJniCallback : public BaseComparatorJniCallback {
  78  public:
  79       ComparatorJniCallback(
  80         JNIEnv* env, jobject jComparator,
  81         const ComparatorJniCallbackOptions* copt);
  82       ~ComparatorJniCallback();
  83 };
  84
  85 class DirectComparatorJniCallback : public BaseComparatorJniCallback {
  86  public:
  87       DirectComparatorJniCallback(
  88         JNIEnv* env, jobject jComparator,
  89         const ComparatorJniCallbackOptions* copt);
  90       ~DirectComparatorJniCallback();
  91 };
  92 }  // namespace rocksdb
  93
  94 #endif  // JAVA_ROCKSJNI_COMPARATORJNICALLBACK_H_