Code/net/minecraft/util/DirectoryLock.java

package net.minecraft.util;

import com.google.common.base.Charsets;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.file.AccessDeniedException;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import net.minecraft.FileUtil;

public class DirectoryLock implements AutoCloseable {
    public static final String LOCK_FILE = "session.lock";
    private final FileChannel lockFile;
    private final FileLock lock;
    private static final ByteBuffer DUMMY;

    public static DirectoryLock create(Path p_13641_) throws IOException {
        Path path = p_13641_.resolve("session.lock");
        FileUtil.createDirectoriesSafe(p_13641_);
        FileChannel filechannel = FileChannel.open(path, StandardOpenOption.CREATE, StandardOpenOption.WRITE);

        try {
            filechannel.write(DUMMY.duplicate());
            filechannel.force(true);
            FileLock filelock = filechannel.tryLock();
            if (filelock == null) {
                throw DirectoryLock.LockException.alreadyLocked(path);
            } else {
                return new DirectoryLock(filechannel, filelock);
            }
        } catch (IOException ioexception1) {
            try {
                filechannel.close();
            } catch (IOException ioexception) {
                ioexception1.addSuppressed(ioexception);
            }

            throw ioexception1;
        }
    }

    private DirectoryLock(FileChannel p_13637_, FileLock p_13638_) {
        this.lockFile = p_13637_;
        this.lock = p_13638_;
    }

    @Override
    public void close() throws IOException {
        try {
            if (this.lock.isValid()) {
                this.lock.release();
            }
        } finally {
            if (this.lockFile.isOpen()) {
                this.lockFile.close();
            }
        }
    }

    public boolean isValid() {
        return this.lock.isValid();
    }

    public static boolean isLocked(Path p_13643_) throws IOException {
        Path path = p_13643_.resolve("session.lock");

        try {
            boolean flag;
            try (
                FileChannel filechannel = FileChannel.open(path, StandardOpenOption.WRITE);
                FileLock filelock = filechannel.tryLock();
            ) {
                flag = filelock == null;
            }

            return flag;
        } catch (AccessDeniedException accessdeniedexception) {
            return true;
        } catch (NoSuchFileException nosuchfileexception) {
            return false;
        }
    }

    static {
        byte[] abyte = "\u2603".getBytes(Charsets.UTF_8);
        DUMMY = ByteBuffer.allocateDirect(abyte.length);
        DUMMY.put(abyte);
        DUMMY.flip();
    }

    public static class LockException extends IOException {
        private LockException(Path p_13646_, String p_13647_) {
            super(p_13646_.toAbsolutePath() + ": " + p_13647_);
        }

        public static DirectoryLock.LockException alreadyLocked(Path p_13649_) {
            return new DirectoryLock.LockException(p_13649_, "already locked (possibly by other Minecraft instance?)");
        }
    }
}