FileLockNamedLockFactory

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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.eclipse.aether.named.providers;

import javax.inject.Named;
import javax.inject.Singleton;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.net.URI;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.eclipse.aether.named.NamedLock;
import org.eclipse.aether.named.NamedLockKey;
import org.eclipse.aether.named.support.FileLockNamedLock;
import org.eclipse.aether.named.support.NamedLockFactorySupport;
import org.eclipse.aether.named.support.NamedLockSupport;

import static org.eclipse.aether.named.support.Retry.retry;

/**
 * Named locks factory of {@link FileLockNamedLock}s. This is a bit of special implementation, as it
 * expects locks names to be proper URI string representations (use {@code file:} protocol for default
 * file system).
 *
 * @since 1.7.3
 */
@Singleton
@Named(FileLockNamedLockFactory.NAME)
public class FileLockNamedLockFactory extends NamedLockFactorySupport {
    public static final String NAME = "file-lock";

    // Logic borrowed from Commons-Lang3: we really need only this, to decide do we "delete on close" or not
    private static final boolean IS_WINDOWS =
            System.getProperty("os.name", "unknown").startsWith("Windows");

    /**
     * Tweak: on Windows, the presence of <em>StandardOpenOption#DELETE_ON_CLOSE</em> causes concurrency issues. This
     * flag allows to have it removed from effective flags, at the cost that lockfile directory becomes crowded
     * with 0 byte sized lock files that are never cleaned up. Default value is {@code true} on non-Windows OS.
     * See <a href="https://bugs.openjdk.org/browse/JDK-8252883">JDK-8252883</a> for Windows related bug. Users
     * on Windows can still force "delete on close" by explicitly setting this property to {@code true}.
     *
     * @see <a href="https://bugs.openjdk.org/browse/JDK-8252883">JDK-8252883</a>
     * @configurationSource {@link System#getProperty(String, String)}
     * @configurationType {@link java.lang.Boolean}
     * @configurationDefaultValue true
     */
    public static final String SYSTEM_PROP_DELETE_LOCK_FILES = "aether.named.file-lock.deleteLockFiles";

    private static final boolean DELETE_LOCK_FILES =
            Boolean.parseBoolean(System.getProperty(SYSTEM_PROP_DELETE_LOCK_FILES, Boolean.toString(!IS_WINDOWS)));

    /**
     * Tweak: on Windows, the presence of <em>StandardOpenOption#DELETE_ON_CLOSE</em> causes concurrency issues. This
     * flag allows to implement similar fix as referenced JDK bug report: retry and hope the best. Default value is
     * 5 attempts (will retry 4 times).
     *
     * @see <a href="https://bugs.openjdk.org/browse/JDK-8252883">JDK-8252883</a>
     * @configurationSource {@link System#getProperty(String, String)}
     * @configurationType {@link java.lang.Integer}
     * @configurationDefaultValue 5
     */
    public static final String SYSTEM_PROP_ATTEMPTS = "aether.named.file-lock.attempts";

    private static final int ATTEMPTS = Integer.parseInt(System.getProperty(SYSTEM_PROP_ATTEMPTS, "5"));

    /**
     * Tweak: When {@link #SYSTEM_PROP_ATTEMPTS} used, the amount of milliseconds to sleep between subsequent retries. Default
     * value is 50 milliseconds.
     *
     * @configurationSource {@link System#getProperty(String, String)}
     * @configurationType {@link java.lang.Long}
     * @configurationDefaultValue 50
     */
    public static final String SYSTEM_PROP_SLEEP_MILLIS = "aether.named.file-lock.sleepMillis";

    private static final long SLEEP_MILLIS = Long.parseLong(System.getProperty(SYSTEM_PROP_SLEEP_MILLIS, "50"));

    private final ConcurrentMap<NamedLockKey, FileChannel> fileChannels;

    public FileLockNamedLockFactory() {
        this.fileChannels = new ConcurrentHashMap<>();
    }

    @Override
    protected NamedLockSupport createLock(final NamedLockKey key) {
        Path path = Paths.get(URI.create(key.name()));
        FileChannel fileChannel = fileChannels.computeIfAbsent(key, k -> openFileChannel(key, path));
        if (!fileChannel.isOpen()) {
            // Channel was closed externally (I/O error, NFS hiccup, etc.). Evict the stale entry
            // and open a fresh one. remove(key, fileChannel) is atomic: it only removes if the
            // value is still this exact (stale) instance, avoiding races with other threads that
            // may have already replaced it.
            fileChannels.remove(key, fileChannel);
            fileChannel = fileChannels.computeIfAbsent(key, k -> openFileChannel(key, path));
        }
        return new FileLockNamedLock(key, fileChannel, this);
    }

    private FileChannel openFileChannel(NamedLockKey key, Path path) {
        try {
            Files.createDirectories(path.getParent());
            FileChannel channel = retry(
                    ATTEMPTS,
                    SLEEP_MILLIS,
                    () -> {
                        if (DELETE_LOCK_FILES) {
                            return FileChannel.open(
                                    path,
                                    StandardOpenOption.READ,
                                    StandardOpenOption.WRITE,
                                    StandardOpenOption.CREATE,
                                    StandardOpenOption.DELETE_ON_CLOSE);
                        } else {
                            return FileChannel.open(
                                    path, StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
                        }
                    },
                    null,
                    null);

            if (channel == null) {
                throw new IllegalStateException(
                        "Could not open file channel for '" + key + "' after " + ATTEMPTS + " attempts; giving up");
            }
            return channel;
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new RuntimeException("Interrupted while opening file channel for '" + key + "'", e);
        } catch (IOException e) {
            throw new UncheckedIOException("Failed to open file channel for '" + key + "'", e);
        }
    }

    @Override
    protected void destroyLock(final NamedLock namedLock) {
        // Keep the FileChannel open in the fileChannels map for reuse by future createLock() calls.
        // Opening a FileChannel is a syscall (open/creat) that shows up as a hotspot when locks are
        // acquired and released frequently (e.g., per-artifact resolution in primed builds).
        // Channels are closed on factory shutdown via doShutdown().
    }

    @Override
    protected void doShutdown() {
        for (FileChannel channel : fileChannels.values()) {
            try {
                channel.close();
            } catch (IOException e) {
                logger.warn("Failed to close file channel", e);
            }
        }
        fileChannels.clear();
    }
}