org.apache.jackrabbit.oak.segment.SegmentBufferWriterPool Maven / Gradle / Ivy
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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.jackrabbit.oak.segment;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.Lists.newArrayList;
import static com.google.common.collect.Maps.newHashMap;
import static com.google.common.collect.Sets.newHashSet;
import static java.lang.Thread.currentThread;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nonnull;
import com.google.common.base.Supplier;
import com.google.common.util.concurrent.Monitor;
import com.google.common.util.concurrent.Monitor.Guard;
/**
* This {@link WriteOperationHandler} uses a pool of {@link SegmentBufferWriter}s,
* which it passes to its {@link #execute(WriteOperation) execute} method.
*
* Instances of this class are thread safe. See also the class comment of
* {@link SegmentWriter}.
*/
public class SegmentBufferWriterPool implements WriteOperationHandler {
/**
* Monitor protecting the state of this pool. Neither of {@link #writers},
* {@link #borrowed} and {@link #disposed} must be modified without owning
* this monitor.
*/
private final Monitor poolMonitor = new Monitor(true);
/**
* Pool of current writers that are not in use
*/
private final Map writers = newHashMap();
/**
* Writers that are currently in use
*/
private final Set borrowed = newHashSet();
/**
* Retired writers that have not yet been flushed
*/
private final Set disposed = newHashSet();
@Nonnull
private final SegmentStore store;
@Nonnull
private final SegmentTracker tracker;
@Nonnull
private final SegmentReader reader;
@Nonnull
private final Supplier gcGeneration;
@Nonnull
private final String wid;
private short writerId = -1;
public SegmentBufferWriterPool(
@Nonnull SegmentStore store,
@Nonnull SegmentTracker tracker,
@Nonnull SegmentReader reader,
@Nonnull String wid,
@Nonnull Supplier gcGeneration) {
this.store = checkNotNull(store);
this.tracker = checkNotNull(tracker);
this.reader = checkNotNull(reader);
this.wid = checkNotNull(wid);
this.gcGeneration = checkNotNull(gcGeneration);
}
@Override
public RecordId execute(WriteOperation writeOperation) throws IOException {
SegmentBufferWriter writer = borrowWriter(currentThread());
try {
return writeOperation.execute(writer);
} finally {
returnWriter(currentThread(), writer);
}
}
@Override
public void flush() throws IOException {
List toFlush = newArrayList();
List toReturn = newArrayList();
poolMonitor.enter();
try {
// Collect all writers that are not currently in use and clear
// the list so they won't get re-used anymore.
toFlush.addAll(writers.values());
writers.clear();
// Collect all borrowed writers, which we need to wait for.
// Clear the list so they will get disposed once returned.
toReturn.addAll(borrowed);
borrowed.clear();
} finally {
poolMonitor.leave();
}
// Wait for the return of the borrowed writers. This is the
// case once all of them appear in the disposed set.
if (safeEnterWhen(poolMonitor, allReturned(toReturn))) {
try {
// Collect all disposed writers and clear the list to mark them
// as flushed.
toFlush.addAll(toReturn);
disposed.removeAll(toReturn);
} finally {
poolMonitor.leave();
}
}
// Call flush from outside the pool monitor to avoid potential
// deadlocks of that method calling SegmentStore.writeSegment
for (SegmentBufferWriter writer : toFlush) {
writer.flush();
}
}
/**
* Create a {@code Guard} that is satisfied if and only if {@link #disposed}
* contains all items in {@code toReturn}
*/
@Nonnull
private Guard allReturned(final List toReturn) {
return new Guard(poolMonitor) {
@Override
public boolean isSatisfied() {
return disposed.containsAll(toReturn);
}
};
}
/**
* Same as {@code monitor.enterWhen(guard)} but copes with that pesky {@code
* InterruptedException} by catching it and setting this thread's
* interrupted flag.
*/
private static boolean safeEnterWhen(Monitor monitor, Guard guard) {
try {
monitor.enterWhen(guard);
return true;
} catch (InterruptedException ignore) {
Thread.currentThread().interrupt();
return false;
}
}
/**
* Return a writer from the pool by its {@code key}. This method may return
* a fresh writer at any time. Callers need to return a writer before
* borrowing it again. Failing to do so leads to undefined behaviour.
*/
private SegmentBufferWriter borrowWriter(Object key) {
poolMonitor.enter();
try {
SegmentBufferWriter writer = writers.remove(key);
if (writer == null) {
writer = new SegmentBufferWriter(store, tracker, reader, getWriterId(wid), gcGeneration.get());
} else if (writer.getGeneration() != gcGeneration.get()) {
disposed.add(writer);
writer = new SegmentBufferWriter(store, tracker, reader, getWriterId(wid), gcGeneration.get());
}
borrowed.add(writer);
return writer;
} finally {
poolMonitor.leave();
}
}
/**
* Return a writer to the pool using the {@code key} that was used to borrow
* it.
*/
private void returnWriter(Object key, SegmentBufferWriter writer) {
poolMonitor.enter();
try {
if (borrowed.remove(writer)) {
checkState(writers.put(key, writer) == null);
} else {
// Defer flush this writer as it was borrowed while flush() was called.
disposed.add(writer);
}
} finally {
poolMonitor.leave();
}
}
private String getWriterId(String wid) {
if (++writerId > 9999) {
writerId = 0;
}
// Manual padding seems to be fastest here
if (writerId < 10) {
return wid + ".000" + writerId;
} else if (writerId < 100) {
return wid + ".00" + writerId;
} else if (writerId < 1000) {
return wid + ".0" + writerId;
} else {
return wid + "." + writerId;
}
}
}