atomix-storage/src/main/java/io/atomix/storage/journal/SegmentedJournalReader.java

   1 /*
   2  * Copyright 2017-2022 Open Networking Foundation and others.  All rights reserved.
   3  * Copyright (c) 2024 PANTHEON.tech, s.r.o.
   4  *
   5  * Licensed under the Apache License, Version 2.0 (the "License");
   6  * you may not use this file except in compliance with the License.
   7  * You may obtain a copy of the License at
   8  *
   9  * http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  */
  17 package io.atomix.storage.journal;
  18
  19 import static java.util.Objects.requireNonNull;
  20
  21 /**
  22  * A {@link JournalReader} traversing all entries.
  23  */
  24 sealed class SegmentedJournalReader<E> implements JournalReader<E> permits CommitsSegmentJournalReader {
  25     final SegmentedJournal<E> journal;
  26
  27     private JournalSegment currentSegment;
  28     private JournalSegmentReader currentReader;
  29     private long nextIndex;
  30
  31     SegmentedJournalReader(final SegmentedJournal<E> journal, final JournalSegment segment) {
  32         this.journal = requireNonNull(journal);
  33         currentSegment = requireNonNull(segment);
  34         currentReader = segment.createReader();
  35         nextIndex = currentSegment.firstIndex();
  36     }
  37
  38     @Override
  39     public final long getFirstIndex() {
  40         return journal.getFirstSegment().firstIndex();
  41     }
  42
  43     @Override
  44     public final long getNextIndex() {
  45         return nextIndex;
  46     }
  47
  48     @Override
  49     public final void reset() {
  50         currentReader.close();
  51
  52         currentSegment = journal.getFirstSegment();
  53         currentReader = currentSegment.createReader();
  54         nextIndex = currentSegment.firstIndex();
  55     }
  56
  57     @Override
  58     public final void reset(final long index) {
  59         // If the current segment is not open, it has been replaced. Reset the segments.
  60         if (!currentSegment.isOpen()) {
  61             reset();
  62         }
  63
  64         if (index < nextIndex) {
  65             rewind(index);
  66         } else if (index > nextIndex) {
  67             while (index > nextIndex && tryNext() != null) {
  68                 // Nothing else
  69             }
  70         } else {
  71             resetCurrentReader(index);
  72         }
  73     }
  74
  75     private void resetCurrentReader(final long index) {
  76         final var position = currentSegment.lookup(index - 1);
  77         if (position != null) {
  78             nextIndex = position.index();
  79             currentReader.setPosition(position.position());
  80         } else {
  81             nextIndex = currentSegment.firstIndex();
  82             currentReader.setPosition(JournalSegmentDescriptor.BYTES);
  83         }
  84         while (nextIndex < index && tryNext() != null) {
  85             // Nothing else
  86         }
  87     }
  88
  89     /**
  90      * Rewinds the journal to the given index.
  91      */
  92     private void rewind(final long index) {
  93         if (currentSegment.firstIndex() >= index) {
  94             JournalSegment segment = journal.getSegment(index - 1);
  95             if (segment != null) {
  96                 currentReader.close();
  97
  98                 currentSegment = segment;
  99                 currentReader = currentSegment.createReader();
 100             }
 101         }
 102
 103         resetCurrentReader(index);
 104     }
 105
 106     @Override
 107     public Indexed<E> tryNext() {
 108         final var index = nextIndex;
 109         var buf = currentReader.readBytes(index);
 110         if (buf == null) {
 111             final var nextSegment = journal.getNextSegment(currentSegment.firstIndex());
 112             if (nextSegment == null || nextSegment.firstIndex() != index) {
 113                 return null;
 114             }
 115
 116             currentReader.close();
 117
 118             currentSegment = nextSegment;
 119             currentReader = currentSegment.createReader();
 120             buf = currentReader.readBytes(index);
 121             if (buf == null) {
 122                 return null;
 123             }
 124         }
 125
 126         final var entry = journal.serializer().deserialize(buf);
 127         nextIndex = index + 1;
 128         return new Indexed<>(index, entry, buf.readableBytes());
 129     }
 130
 131     @Override
 132     public final void close() {
 133         currentReader.close();
 134         journal.closeReader(this);
 135     }
 136 }