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HDFS-5746. Add ShortCircuitSharedMemorySegment (cmccabe)
git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1563362 13f79535-47bb-0310-9956-ffa450edef68
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...adoop-common/src/main/java/org/apache/hadoop/io/nativeio/SharedFileDescriptorFactory.java
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| /** | ||
| * 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. | ||
| */ | ||
| package org.apache.hadoop.io.nativeio; | ||
|
|
||
| import java.io.FileInputStream; | ||
| import java.io.IOException; | ||
| import java.io.FileDescriptor; | ||
|
|
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| import org.apache.commons.lang.SystemUtils; | ||
| import org.apache.hadoop.classification.InterfaceAudience; | ||
| import org.apache.hadoop.classification.InterfaceStability; | ||
|
|
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| import com.google.common.base.Preconditions; | ||
|
|
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| /** | ||
| * A factory for creating shared file descriptors inside a given directory. | ||
| * Typically, the directory will be /dev/shm or /tmp. | ||
| * | ||
| * We will hand out file descriptors that correspond to unlinked files residing | ||
| * in that directory. These file descriptors are suitable for sharing across | ||
| * multiple processes and are both readable and writable. | ||
| * | ||
| * Because we unlink the temporary files right after creating them, a JVM crash | ||
| * usually does not leave behind any temporary files in the directory. However, | ||
| * it may happen that we crash right after creating the file and before | ||
| * unlinking it. In the constructor, we attempt to clean up after any such | ||
| * remnants by trying to unlink any temporary files created by previous | ||
| * SharedFileDescriptorFactory instances that also used our prefix. | ||
| */ | ||
| @InterfaceAudience.Private | ||
| @InterfaceStability.Unstable | ||
| public class SharedFileDescriptorFactory { | ||
| private final String prefix; | ||
| private final String path; | ||
|
|
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| /** | ||
| * Create a SharedFileDescriptorFactory. | ||
| * | ||
| * @param prefix Prefix to add to all file names we use. | ||
| * @param path Path to use. | ||
| */ | ||
| public SharedFileDescriptorFactory(String prefix, String path) | ||
| throws IOException { | ||
| Preconditions.checkArgument(NativeIO.isAvailable()); | ||
| Preconditions.checkArgument(SystemUtils.IS_OS_UNIX); | ||
| this.prefix = prefix; | ||
| this.path = path; | ||
| deleteStaleTemporaryFiles0(prefix, path); | ||
| } | ||
|
|
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| /** | ||
| * Create a shared file descriptor which will be both readable and writable. | ||
| * | ||
| * @param length The starting file length. | ||
| * | ||
| * @return The file descriptor, wrapped in a FileInputStream. | ||
| * @throws IOException If there was an I/O or configuration error creating | ||
| * the descriptor. | ||
| */ | ||
| public FileInputStream createDescriptor(int length) throws IOException { | ||
| return new FileInputStream(createDescriptor0(prefix, path, length)); | ||
| } | ||
|
|
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| /** | ||
| * Delete temporary files in the directory, NOT following symlinks. | ||
| */ | ||
| private static native void deleteStaleTemporaryFiles0(String prefix, | ||
| String path) throws IOException; | ||
|
|
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| /** | ||
| * Create a file with O_EXCL, and then resize it to the desired size. | ||
| */ | ||
| private static native FileDescriptor createDescriptor0(String prefix, | ||
| String path, int length) throws IOException; | ||
| } |
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