2 * Copyright (c) 2024 PANTHEON.tech, s.r.o. and others. All rights reserved.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
16 package io.atomix.storage.journal;
18 import static com.google.common.base.Verify.verify;
19 import static java.util.Objects.requireNonNull;
21 import io.netty.buffer.ByteBuf;
22 import java.io.IOException;
23 import java.nio.channels.FileChannel;
24 import org.eclipse.jdt.annotation.NonNull;
27 * A {@link StorageLevel#DISK} implementation of {@link FileReader}. Maintains an internal buffer.
29 final class DiskFileReader extends FileReader {
30 private final FileChannel channel;
32 private ByteBuf buffer;
33 // tracks where memory's first available byte maps to in terms of FileChannel.position()
34 private int bufferPosition;
36 // Note: take ownership of the buffer
37 DiskFileReader(final JournalSegmentFile file, final ByteBuf buffer) {
39 this.buffer = requireNonNull(buffer);
40 channel = file.channel();
45 void invalidateCache() {
51 ByteBuf read(final int position, final int size) {
52 // calculate logical seek distance between buffer's first byte and position and split flow between
53 // forward-moving and backwards-moving code paths.
54 final int seek = bufferPosition - position;
55 return seek >= 0 ? forwardAndRead(seek, position, size) : rewindAndRead(-seek, position, size);
60 final var local = buffer;
67 private @NonNull ByteBuf forwardAndRead(final int seek, final int position, final int size) {
68 final int remaining = buffer.writerIndex() - seek;
69 final int missing = remaining - size;
71 // fast path: we have the requested region
72 return buffer.slice(seek, size).asReadOnly();
75 // We need to read more data, but let's salvage what we can:
76 // - set buffer position to seek, which means it points to the same as position
77 // - run compact, which moves everything between position and limit onto the beginning of buffer and
78 // sets it up to receive more bytes
79 // - start the read accounting for the seek
80 buffer.writeBytes(buffer, seek, remaining);
81 readAtLeast(position + seek, missing);
82 return setAndSlice(position, size);
85 private @NonNull ByteBuf rewindAndRead(final int rewindBy, final int position, final int size) {
86 // TODO: Lazy solution. To be super crisp, we want to find out how much of the buffer we can salvage and
87 // do all the limit/position fiddling before and after read. Right now let's just flow the buffer up and
90 readAtLeast(position, size);
91 return setAndSlice(position, size);
94 private void readAtLeast(final int readPosition, final int readAtLeast) {
97 bytesRead = buffer.writeBytes(channel, readPosition, readAtLeast);
98 } catch (IOException e) {
99 throw new StorageException(e);
101 verify(bytesRead >= readAtLeast, "Short read %s, expected %s", bytesRead, readAtLeast);
104 private @NonNull ByteBuf setAndSlice(final int position, final int size) {
105 bufferPosition = position;
106 return buffer.slice(0, size).asReadOnly();