gradle-master/subprojects/persistent-cache/src/main/java/org/gradle/cache/internal/filelock/LockInfoAccess.java
/*
 * Copyright 2013 the original author or authors.
 *
 * 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 org.gradle.cache.internal.filelock;

import org.gradle.internal.io.RandomAccessFileInputStream;
import org.gradle.internal.io.RandomAccessFileOutputStream;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;

public class LockInfoAccess {
    public static final int INFORMATION_REGION_SIZE = 2052;
    private final LockInfoSerializer lockInfoSerializer = new LockInfoSerializer();
    private final long infoRegionPos;

    public LockInfoAccess(long infoRegionPos) {
        this.infoRegionPos = infoRegionPos;
    }

    public LockInfo readLockInfo(RandomAccessFile lockFileAccess) throws IOException {
        if (lockFileAccess.length() <= infoRegionPos) {
            return new LockInfo();
        } else {
            lockFileAccess.seek(infoRegionPos);

            DataInputStream inputStream = new DataInputStream(new BufferedInputStream(new RandomAccessFileInputStream(lockFileAccess)));
            byte protocolVersion = inputStream.readByte();
            if (protocolVersion != lockInfoSerializer.getVersion()) {
                throw new IllegalStateException(String.format("Unexpected lock protocol found in lock file. Expected %s, found %s.", lockInfoSerializer.getVersion(), protocolVersion));
            }

            return lockInfoSerializer.read(inputStream);
        }
    }

    public void writeLockInfo(RandomAccessFile lockFileAccess, LockInfo lockInfo) throws IOException {
        lockFileAccess.seek(infoRegionPos);

        DataOutputStream outstr = new DataOutputStream(new BufferedOutputStream(new RandomAccessFileOutputStream(lockFileAccess)));
        outstr.writeByte(lockInfoSerializer.getVersion());
        lockInfoSerializer.write(outstr, lockInfo);
        outstr.flush();

        lockFileAccess.setLength(lockFileAccess.getFilePointer());
    }

    public void clearLockInfo(RandomAccessFile lockFileAccess) throws IOException {
        lockFileAccess.setLength(Math.min(lockFileAccess.length(), infoRegionPos));
    }

    public FileLockOutcome tryLock(RandomAccessFile lockFileAccess, boolean shared) throws IOException {
        try {
            FileLock fileLock = lockFileAccess.getChannel().tryLock(infoRegionPos, INFORMATION_REGION_SIZE - infoRegionPos, shared);
            if (fileLock == null) {
                return FileLockOutcome.LOCKED_BY_ANOTHER_PROCESS;
            } else {
                return FileLockOutcome.acquired(fileLock);
            }
        } catch (OverlappingFileLockException e) {
            // Locked by this process, treat as not acquired
            return FileLockOutcome.LOCKED_BY_THIS_PROCESS;
        }
    }

}
