net.oneandone.stool.locking.Store Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of main Show documentation
Stool's main component. Java Library, cli, setup code.
There is a newer version: 4.0.3
/*
 * Copyright 1&1 Internet AG, https://github.com/1and1/
 *
 * Licensed 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 net.oneandone.stool.locking;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.ArrayList;
import java.util.List;

/** Persistent representation of locks. Internal class. */
public class Store {
    private static final char PROCESS = '@';
    private static final char EXCLUSIVE = '!';
    private static final char SHARED = '.';

    public static Store load(RandomAccessFile raf) throws IOException {
        Store result;
        String line;
        Process last;
        Queue queue;
        char marker;
        Mode mode;

        result = new Store();
        raf.seek(0);
        last = null;
        for (line = raf.readLine(); line != null; line = raf.readLine()) {
            if (line.isEmpty()) {
                throw new IllegalStateException();
            }
            marker = line.charAt(0);
            if (marker == PROCESS) {
                last = Process.parse(line.substring(1));
            } else {
                switch (marker) {
                    case SHARED:
                        mode = Mode.SHARED;
                        break;
                    case EXCLUSIVE:
                        mode = Mode.EXCLUSIVE;
                        break;
                    default:
                        throw new IllegalStateException("unexpected marker: " + marker);
                }
                if (last == null) {
                    throw new IllegalStateException();
                }
                queue = result.getOrCreate(line.substring(1));
                if (!queue.tryLock(mode.toSharedExclusive(), last)) {
                    throw new IllegalStateException();
                }
            }
        }
        return result;
    }

    private final List queues;

    public Store() {
        this.queues = new ArrayList<>();
    }

    public boolean isEmpty() {
        return queues.isEmpty();
    }

    public Queue lookup(String lock) {
        for (Queue queue : queues) {
            if (queue.is(lock)) {
                return queue;
            }
        }
        return null;
    }

    /** @return null for success, problematic queue otherwise */
    public Queue tryLock(String lock, Mode mode, Process processExtern) {
        Process process;
        Queue queue;

        if (mode == Mode.NONE) {
            return null;
        }
        process = intern(processExtern);
        queue = lookup(lock);
        if (queue == null) {
            queue = new Queue(lock);
            if (!queue.tryLock(mode.toSharedExclusive(), process)) {
                throw new IllegalStateException();
            }
            queues.add(queue);
        } else {
            if (!queue.tryLock(mode.toSharedExclusive(), process)) {
                return queue;
            }
        }
        return null;
    }

    public void release(String lock, Mode mode, Process processExtern) {
        Process process;
        Queue queue;

        if (mode == Mode.NONE) {
            return;
        }
        process = intern(processExtern);
        queue = lookup(lock);
        if (queue == null) {
            throw new IllegalStateException(lock);
        }
        queue.release(mode.toSharedExclusive(), process);
    }

    public void releaseAll(Process processExtern) {
        Process process;

        process = intern(processExtern);
        for (Queue queue : queues) {
            queue.releaseAll(process);
        }
    }

    private Process intern(Process extern) {
        for (Process intern : processes()) {
            if (intern.id == extern.id) {
                return intern;
            }
        }
        return extern;
    }

    public void save(RandomAccessFile raf) throws IOException {
        List queues;

        raf.seek(0);
        raf.setLength(0);
        for (Process process : processes()) {
            queues = queuesWithProcess(process);
            if (!queues.isEmpty()) {
                line(raf, PROCESS, process.toLine());
                for (Queue queue : queues) {
                    if (process == queue.exclusiveProcess) {
                        for (int count = queue.exclusiveCount; count > 0; count--) {
                            line(raf, EXCLUSIVE, queue.lock);
                        }
                    }
                    for (Process e : queue.shared) {
                        if (process == e) {
                            line(raf, SHARED, queue.lock);
                        }
                    }
                }
            }
        }
    }

    public List processes() {
        List result;

        result = new ArrayList<>();
        for (Queue queue : queues) {
            processes(queue, result);
        }
        return result;
    }

    private static void processes(Queue queue, List result) {
        if (queue.exclusiveCount > 0) {
            addOpt(result, queue.exclusiveProcess);
        }
        for (Process process : queue.shared) {
            addOpt(result, process);
        }
    }
    private static void addOpt(List result, Process process) {
        if (!result.contains(process)) {
            result.add(process);
        }
    }

    private List queuesWithProcess(Process process) {
        List result;

        result = new ArrayList<>();
        for (Queue queue : queues) {
            if (queue.contains(process)) {
                if (!result.contains(queue)) {
                    result.add(queue);
                }
            }
        }
        return result;
    }

    private static void line(RandomAccessFile raf, char marker, String line) throws IOException {
        raf.writeByte(marker);
        raf.writeBytes(line);
        raf.writeByte('\n');
    }

    private Queue getOrCreate(String name) {
        Queue result;

        for (Queue queue : queues) {
            if (queue.is(name)) {
                return queue;
            }
        }
        result = new Queue(name);
        queues.add(result);
        return result;
    }
}