toddlipcon commented on a change in pull request #595: HDFS-14304: High lock contention on hdfsHashMutex in libhdfs URL: https://github.com/apache/hadoop/pull/595#discussion_r267052771
########## File path: hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/jclasses.h ########## @@ -0,0 +1,117 @@ +/** + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#ifndef LIBHDFS_JCLASSES_H +#define LIBHDFS_JCLASSES_H + +#include <jni.h> + +/** + * Encapsulates logic to cache jclass objects so they can re-used across + * calls to FindClass. Creating jclass objects every time libhdfs has to + * invoke a method can hurt performance. By cacheing jclass objects we avoid + * this overhead. + * + * We use the term "cached" here loosely; jclasses are not truly cached, + * instead they are created once during JVM load and are kept alive until the + * process shutdowns. There is no eviction of jclass objects. + * + * @see https://www.ibm.com/developerworks/library/j-jni/index.html#notc + */ + +/** + * Each enum value represents one jclass that is cached. Enum values should + * be passed to getJclass or getName to get the jclass object or class name + * represented by the enum value. + */ +typedef enum { + JC_CONFIGURATION, + JC_PATH, + JC_FILE_SYSTEM, + JC_FS_STATUS, + JC_FILE_UTIL, + JC_BLOCK_LOCATION, + JC_DFS_HEDGED_READ_METRICS, + JC_DISTRIBUTED_FILE_SYSTEM, + JC_FS_DATA_INPUT_STREAM, + JC_FS_DATA_OUTPUT_STREAM, + JC_FILE_STATUS, + JC_FS_PERMISSION, + JC_READ_STATISTICS, + JC_HDFS_DATA_INPUT_STREAM, + JC_DOMAIN_SOCKET, + JC_URI, + JC_BYTE_BUFFER, + JC_ENUM_SET, + JC_EXCEPTION_UTILS, + // A special marker enum that counts the number of cached jclasses + NUM_CACHED_CLASSES +} CachedJavaClass; + +/** + * Whether initCachedClasses has been called or not. Protected by the mutex + * jclassInitMutex. + */ +extern int jclassesInitialized; Review comment: Instead of exposing this externally from jclasses.h I think it'd be better to just unconditionally call initCachedClasses() and make it internally decide whether to no-op it. That's a cold code path (only once per thread) so avoiding the non-inlined function call isn't important ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: common-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: common-issues-h...@hadoop.apache.org
