expose write buffer manager memory usage methods through Java Api

java/Makefile

@@ -105,7 +105,7 @@ ARCH := $(shell getconf LONG_BIT)
 SHA256_CMD ?= sha256sum
 
 JAVA_TESTS = \
-	org.rocksdb.BackupableDBOptionsTest\
+org.rocksdb.BackupableDBOptionsTest\
 	org.rocksdb.BackupEngineTest\
 	org.rocksdb.BlockBasedTableConfigTest\
 	org.rocksdb.BuiltinComparatorTest\
@@ -189,7 +189,8 @@ JAVA_TESTS = \
 	org.rocksdb.WriteBatchTest\
 	org.rocksdb.WriteBatchThreadedTest\
 	org.rocksdb.WriteOptionsTest\
-	org.rocksdb.WriteBatchWithIndexTest
+	org.rocksdb.WriteBatchWithIndexTest\
+	org.rocksdb.WriteBufferManagerTest
 
 MAIN_SRC = src/main/java
 TEST_SRC = src/test/java
@@ -282,7 +283,7 @@ ifeq ($(shell java -version 2>&1 | grep 1.7.0 > /dev/null; printf $$?), 0)
 endif
 
 sample: java
-	$(AM_V_GEN)mkdir -p $(SAMPLES_MAIN_CLASSES)
+	$(AM_V_GEN)mkdir -p $(SAMPLES_MAIN_CLASSE
 	$(AM_V_at)javac $(JAVAC_ARGS) -cp $(MAIN_CLASSES) -d $(SAMPLES_MAIN_CLASSES) $(SAMPLES_MAIN_SRC)/RocksDBSample.java
 	$(AM_V_at)@rm -rf /tmp/rocksdbjni
 	$(AM_V_at)@rm -rf /tmp/rocksdbjni_not_found

java/rocksjni/write_buffer_manager.cc

@@ -27,6 +27,20 @@ jlong Java_org_rocksdb_WriteBufferManager_newWriteBufferManager(
   return reinterpret_cast<jlong>(write_buffer_manager);
 }
 
+/*
+ * Class:     org_rocksdb_WriteBufferManager
+ * Method:    newWriteBufferManagerWithoutCache
+ * Signature: (JJ)J
+ */
+jlong Java_org_rocksdb_WriteBufferManager_newWriteBufferManagerWithoutCache(
+    JNIEnv* /*env*/, jclass /*jclazz*/, jlong jbuffer_size) {
+  auto* write_buffer_manager =
+      new std::shared_ptr<ROCKSDB_NAMESPACE::WriteBufferManager>(
+          std::make_shared<ROCKSDB_NAMESPACE::WriteBufferManager>(jbuffer_size,
+                                                                  nullptr));
+  return reinterpret_cast<jlong>(write_buffer_manager);
+}
+
 /*
  * Class:     org_rocksdb_WriteBufferManager
  * Method:    disposeInternal
@@ -40,3 +54,47 @@ void Java_org_rocksdb_WriteBufferManager_disposeInternal(
   assert(write_buffer_manager != nullptr);
   delete write_buffer_manager;
 }
+
+/*
+ * Class:     org_rocksdb_WriteBufferManager
+ * Method:    getMemoryUsage
+ * Signature: (J)J
+ */
+jlong Java_org_rocksdb_WriteBufferManager_getMemoryUsage(JNIEnv* /*env*/,
+                                                         jobject,
+                                                         jlong jhandle) {
+  auto* write_buffer_manager =
+      reinterpret_cast<std::shared_ptr<ROCKSDB_NAMESPACE::WriteBufferManager>*>(
+          jhandle);
+  assert(write_buffer_manager != nullptr);
+  return static_cast<jlong>(write_buffer_manager->get()->memory_usage());
+}
+
+/*
+ * Class:     org_rocksdb_WriteBufferManager
+ * Method:    getMutableMemtableMemoryUsage
+ * Signature: (J)J
+ */
+jlong Java_org_rocksdb_WriteBufferManager_getMutableMemtableMemoryUsage(
+    JNIEnv* /*env*/, jobject, jlong jhandle) {
+  auto* write_buffer_manager =
+      reinterpret_cast<std::shared_ptr<ROCKSDB_NAMESPACE::WriteBufferManager>*>(
+          jhandle);
+  assert(write_buffer_manager != nullptr);
+  return static_cast<jlong>(
+      write_buffer_manager->get()->mutable_memtable_memory_usage());
+}
+
+/*
+ * Class:     org_rocksdb_WriteBufferManager
+ * Method:    getBufferSize
+ * Signature: (J)J
+ */
+jlong Java_org_rocksdb_WriteBufferManager_getBufferSize(JNIEnv*, jobject,
+                                                        jlong jhandle) {
+  auto* write_buffer_manager =
+      reinterpret_cast<std::shared_ptr<ROCKSDB_NAMESPACE::WriteBufferManager>*>(
+          jhandle);
+  assert(write_buffer_manager != nullptr);
+  return static_cast<jlong>(write_buffer_manager->get()->buffer_size());
+}

java/src/main/java/org/rocksdb/WriteBufferManager.java

@@ -9,25 +9,82 @@
  * Java wrapper over native write_buffer_manager class
  */
 public class WriteBufferManager extends RocksObject {
-  static {
-    RocksDB.loadLibrary();
-  }
 
   /**
    * Construct a new instance of WriteBufferManager.
    *
-   * Check <a href="https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager">
-   *     https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager</a>
-   * for more details on when to use it
+   * Check
+   * <a href="https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager">
+   * https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager</a> for more
+   * details on when to use it
    *
-   * @param bufferSizeBytes buffer size(in bytes) to use for native write_buffer_manager
-   * @param cache cache whose memory should be bounded by this write buffer manager
+   * @param bufferSizeBytes buffer size(in bytes) to use for native
+   *                        write_buffer_manager
+   * @param cache           cache whose memory should be bounded by this write
+   *                        buffer manager
    */
-  public WriteBufferManager(final long bufferSizeBytes, final Cache cache){
+  public WriteBufferManager(final long bufferSizeBytes, final Cache cache) {
     super(newWriteBufferManager(bufferSizeBytes, cache.nativeHandle_));
   }
 
+  /**
+   * Construct a new instance of WriteBufferManager.
+   *
+   * Check
+   * <a href="https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager">
+   * https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager</a> for more
+   * details on when to use it
+   *
+   * @param bufferSizeBytes buffer size(in bytes) to use for native
+   *                        write_buffer_manager
+   */
+  public WriteBufferManager(final long bufferSizeBytes) {
+    super(newWriteBufferManagerWithoutCache(bufferSizeBytes));
+  }
+
+  /**
+   * Returns the buffer size of the write buffer manager
+   *
+   * @return buffer size.
+   *
+   */
+  public long getBufferSize() {
+    assert (isOwningHandle());
+    return getBufferSize(this.nativeHandle_);
+  }
+
+  /**
+   * Returns the memory usage of the write buffer manager
+   *
+   * @return memory usage.
+   *
+   */
+  public long getMemoryUsage() {
+    assert (isOwningHandle());
+    return getMemoryUsage(this.nativeHandle_);
+  }
+
+  /**
+   * Returns the mutable memtable memory usage of the write buffer manager
+   *
+   * @return mutable memtable memory usage size.
+   *
+   */
+  public long getMutableMemtableMemoryUsage() {
+    assert (isOwningHandle());
+    return getMutableMemtableMemoryUsage(this.nativeHandle_);
+  }
+
   private native static long newWriteBufferManager(final long bufferSizeBytes, final long cacheHandle);
+
+  private native static long newWriteBufferManagerWithoutCache(final long bufferSizeBytes);
+
+  private native static long getMemoryUsage(final long handle);
+
+  private native static long getMutableMemtableMemoryUsage(final long handle);
+
+  private native static long getBufferSize(final long handle);
+
   @Override
   protected native void disposeInternal(final long handle);
 }

java/src/test/java/org/rocksdb/WriteBufferManagerTest.java

@@ -0,0 +1,38 @@
+// 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).
+
+package org.rocksdb;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.ClassRule;
+import org.junit.Test;
+
+public class WriteBufferManagerTest {
+
+  @ClassRule
+  public static final RocksNativeLibraryResource ROCKS_NATIVE_LIBRARY_RESOURCE = new RocksNativeLibraryResource();
+
+  @Test
+  public void newWriteBufferManagerWithCache() {
+    final long capacity = 1000;
+    try (final Cache lruCache = new LRUCache(capacity);
+         final WriteBufferManager wbm = new WriteBufferManager(capacity, lruCache)) {
+      assertThat(wbm.getBufferSize()).isEqualTo(capacity);
+      assertThat(wbm.getMemoryUsage()).isEqualTo(0);
+      assertThat(wbm.getMutableMemtableMemoryUsage()).isEqualTo(0);
+    }
+  }
+
+  @Test
+  public void newWriteBufferManagerWithoutCache() {
+    final long capacity = 1000;
+    try (final WriteBufferManager wbm = new WriteBufferManager(capacity)) {
+      assertThat(wbm.getBufferSize()).isEqualTo(capacity);
+      assertThat(wbm.getMemoryUsage()).isEqualTo(0);
+      assertThat(wbm.getMutableMemtableMemoryUsage()).isEqualTo(0);
+    }
+  }
+}