| /* |
| * 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.lucene.store; |
| |
| import java.io.IOException; |
| import java.nio.ByteBuffer; |
| import java.nio.LongBuffer; |
| import java.util.concurrent.atomic.AtomicInteger; |
| |
| /** |
| * A guard that is created for every {@link ByteBufferIndexInput} that tries on best effort |
| * to reject any access to the {@link ByteBuffer} behind, once it is unmapped. A single instance |
| * of this is used for the original and all clones, so once the original is closed and unmapped |
| * all clones also throw {@link AlreadyClosedException}, triggered by a {@link NullPointerException}. |
| * <p> |
| * This code tries to hopefully flush any CPU caches using a store-store barrier. It also yields the |
| * current thread to give other threads a chance to finish in-flight requests... |
| */ |
| final class ByteBufferGuard { |
| |
| /** |
| * Pass in an implementation of this interface to cleanup ByteBuffers. |
| * MMapDirectory implements this to allow unmapping of bytebuffers with private Java APIs. |
| */ |
| @FunctionalInterface |
| static interface BufferCleaner { |
| void freeBuffer(String resourceDescription, ByteBuffer b) throws IOException; |
| } |
| |
| private final String resourceDescription; |
| private final BufferCleaner cleaner; |
| |
| /** Not volatile; see comments on visibility below! */ |
| private boolean invalidated = false; |
| |
| /** Used as a store-store barrier; see comments below! */ |
| private final AtomicInteger barrier = new AtomicInteger(); |
| |
| /** |
| * Creates an instance to be used for a single {@link ByteBufferIndexInput} which |
| * must be shared by all of its clones. |
| */ |
| public ByteBufferGuard(String resourceDescription, BufferCleaner cleaner) { |
| this.resourceDescription = resourceDescription; |
| this.cleaner = cleaner; |
| } |
| |
| /** |
| * Invalidates this guard and unmaps (if supported). |
| */ |
| public void invalidateAndUnmap(ByteBuffer... bufs) throws IOException { |
| if (cleaner != null) { |
| invalidated = true; |
| // This call should hopefully flush any CPU caches and as a result make |
| // the "invalidated" field update visible to other threads. We specifically |
| // don't make "invalidated" field volatile for performance reasons, hoping the |
| // JVM won't optimize away reads of that field and hardware should ensure |
| // caches are in sync after this call. This isn't entirely "fool-proof" |
| // (see LUCENE-7409 discussion), but it has been shown to work in practice |
| // and we count on this behavior. |
| barrier.lazySet(0); |
| // we give other threads a bit of time to finish reads on their ByteBuffer...: |
| Thread.yield(); |
| // finally unmap the ByteBuffers: |
| for (ByteBuffer b : bufs) { |
| cleaner.freeBuffer(resourceDescription, b); |
| } |
| } |
| } |
| |
| private void ensureValid() { |
| if (invalidated) { |
| // this triggers an AlreadyClosedException in ByteBufferIndexInput: |
| throw new NullPointerException(); |
| } |
| } |
| |
| public void getBytes(ByteBuffer receiver, byte[] dst, int offset, int length) { |
| ensureValid(); |
| receiver.get(dst, offset, length); |
| } |
| |
| public byte getByte(ByteBuffer receiver) { |
| ensureValid(); |
| return receiver.get(); |
| } |
| |
| public short getShort(ByteBuffer receiver) { |
| ensureValid(); |
| return receiver.getShort(); |
| } |
| |
| public int getInt(ByteBuffer receiver) { |
| ensureValid(); |
| return receiver.getInt(); |
| } |
| |
| public long getLong(ByteBuffer receiver) { |
| ensureValid(); |
| return receiver.getLong(); |
| } |
| |
| public byte getByte(ByteBuffer receiver, int pos) { |
| ensureValid(); |
| return receiver.get(pos); |
| } |
| |
| public short getShort(ByteBuffer receiver, int pos) { |
| ensureValid(); |
| return receiver.getShort(pos); |
| } |
| |
| public int getInt(ByteBuffer receiver, int pos) { |
| ensureValid(); |
| return receiver.getInt(pos); |
| } |
| |
| public long getLong(ByteBuffer receiver, int pos) { |
| ensureValid(); |
| return receiver.getLong(pos); |
| } |
| |
| public void getLongs(LongBuffer receiver, long[] dst, int offset, int length) { |
| ensureValid(); |
| receiver.get(dst, offset, length); |
| } |
| |
| } |