core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLock.java

package org.onlab.onos.store.service.impl;

import static org.slf4j.LoggerFactory.getLogger;

import java.nio.charset.StandardCharsets;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;

import org.joda.time.DateTime;
import org.onlab.onos.cluster.ClusterService;
import org.onlab.onos.store.service.DatabaseService;
import org.onlab.onos.store.service.Lock;
import org.slf4j.Logger;

/**
 * A distributed lock implementation.
 */
public class DistributedLock implements Lock {

    private final Logger log = getLogger(getClass());

    private static final long MAX_WAIT_TIME_MS = 100000000L;

    private final DistributedLockManager lockManager;
    private final DatabaseService databaseService;
    private final String path;
    private DateTime lockExpirationTime;
    private AtomicBoolean isLocked = new AtomicBoolean(false);
    private byte[] lockId;

    public DistributedLock(
            String path,
            DatabaseService databaseService,
            ClusterService clusterService,
            DistributedLockManager lockManager) {

        this.path = path;
        this.databaseService = databaseService;
        this.lockManager = lockManager;
        this.lockId =
                (UUID.randomUUID().toString() + "::" +
                        clusterService.getLocalNode().id().toString()).
                        getBytes(StandardCharsets.UTF_8);
    }

    @Override
    public String path() {
        return path;
    }

    @Override
    public void lock(int leaseDurationMillis) {
        if (isLocked() && lockExpirationTime.isAfter(DateTime.now().plusMillis(leaseDurationMillis))) {
            // Nothing to do.
            // Current expiration time is beyond what is requested.
            return;
        } else {
            tryLock(MAX_WAIT_TIME_MS, leaseDurationMillis);
        }
    }

    @Override
    public boolean tryLock(int leaseDurationMillis) {
        if (databaseService.putIfAbsent(
                DistributedLockManager.ONOS_LOCK_TABLE_NAME,
                path,
                lockId)) {
            isLocked.set(true);
            lockExpirationTime = DateTime.now().plusMillis(leaseDurationMillis);
            return true;
        }
        return false;
    }

    @Override
    public boolean tryLock(
            long waitTimeMillis,
            int leaseDurationMillis) {
        if (tryLock(leaseDurationMillis)) {
            return true;
        }

        CompletableFuture<DateTime> future =
                lockManager.lockIfAvailable(this, waitTimeMillis, leaseDurationMillis);
        try {
            lockExpirationTime = future.get(waitTimeMillis, TimeUnit.MILLISECONDS);
            return true;
        } catch (ExecutionException | InterruptedException e) {
            log.error("Encountered an exception trying to acquire lock for " + path, e);
            // TODO: ExecutionException could indicate something
            // wrong with the backing database.
            // Throw an exception?
            return false;
        } catch (TimeoutException e) {
            log.debug("Timed out waiting to acquire lock for {}", path);
            return false;
        }
    }

    @Override
    public boolean isLocked() {
        if (isLocked.get()) {
            // We rely on local information to check
            // if the lock expired.
            // This should should make this call
            // light weight, while still retaining the
            // safety guarantees.
            if (DateTime.now().isAfter(lockExpirationTime)) {
                isLocked.set(false);
                return false;
            } else {
                return true;
            }
        }
        return false;
    }

    @Override
    public void unlock() {
        if (!isLocked()) {
            return;
        } else {
            if (databaseService.removeIfValueMatches(DistributedLockManager.ONOS_LOCK_TABLE_NAME, path, lockId)) {
                isLocked.set(false);
            }
        }
    }

    @Override
    public boolean extendExpiration(int leaseDurationMillis) {
        if (!isLocked()) {
            log.warn("Ignoring request to extend expiration for lock {}."
                    + " ExtendExpiration must be called for locks that are already acquired.", path);
            return false;
        }

        if (databaseService.putIfValueMatches(
                DistributedLockManager.ONOS_LOCK_TABLE_NAME,
                path,
                lockId,
                lockId)) {
            lockExpirationTime = DateTime.now().plusMillis(leaseDurationMillis);
            log.debug("Succeeded in extending lock {} expiration time to {}", lockExpirationTime);
            return true;
        } else {
            log.info("Failed to extend expiration for {}", path);
            return false;
        }
    }
}