flink-core/src/main/java/org/apache/flink/util/AbstractCloseableRegistry.java

/*
 * 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.apache.flink.util;

import org.apache.flink.annotation.Internal;
import org.apache.flink.annotation.VisibleForTesting;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.GuardedBy;

import java.io.Closeable;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;

/**
 * This is the abstract base class for registries that allow to register instances of {@link
 * Closeable}, which are all closed if this registry is closed.
 *
 * <p>Registering to an already closed registry will throw an exception and close the provided
 * {@link Closeable}
 *
 * <p>All methods in this class are thread-safe.
 *
 * @param <C> Type of the closeable this registers
 * @param <T> Type for potential meta data associated with the registering closeables
 */
@Internal
public abstract class AbstractCloseableRegistry<C extends Closeable, T> implements Closeable {

    /** Lock that guards state of this registry. * */
    private final Object lock;

    /** Map from tracked Closeables to some associated meta data. */
    @GuardedBy("lock")
    protected final Map<Closeable, T> closeableToRef;

    /** Indicates if this registry is closed. */
    @GuardedBy("lock")
    private boolean closed;

    public AbstractCloseableRegistry(@Nonnull Map<Closeable, T> closeableToRef) {
        this.lock = new Object();
        this.closeableToRef = Preconditions.checkNotNull(closeableToRef);
        this.closed = false;
    }

    /**
     * Registers a {@link Closeable} with the registry. In case the registry is already closed, this
     * method throws an {@link IllegalStateException} and closes the passed {@link Closeable}.
     *
     * @param closeable Closeable tor register
     * @throws IOException exception when the registry was closed before
     */
    public final void registerCloseable(C closeable) throws IOException {

        if (null == closeable) {
            return;
        }

        synchronized (getSynchronizationLock()) {
            if (!closed) {
                doRegister(closeable, closeableToRef);
                return;
            }
        }

        IOUtils.closeQuietly(closeable);
        throw new IOException(
                "Cannot register Closeable, registry is already closed. Closing argument.");
    }

    /**
     * Removes a {@link Closeable} from the registry.
     *
     * @param closeable instance to remove from the registry.
     * @return true if the closeable was previously registered and became unregistered through this
     *     call.
     */
    public final boolean unregisterCloseable(C closeable) {

        if (null == closeable) {
            return false;
        }

        synchronized (getSynchronizationLock()) {
            return doUnRegister(closeable, closeableToRef);
        }
    }

    @Override
    public void close() throws IOException {
        Collection<Closeable> toCloseCopy;

        synchronized (getSynchronizationLock()) {
            if (closed) {
                return;
            }

            closed = true;

            toCloseCopy = getReferencesToClose();

            closeableToRef.clear();
        }

        IOUtils.closeAllQuietly(toCloseCopy);
    }

    public boolean isClosed() {
        synchronized (getSynchronizationLock()) {
            return closed;
        }
    }

    protected Collection<Closeable> getReferencesToClose() {
        return new ArrayList<>(closeableToRef.keySet());
    }

    /**
     * Does the actual registration of the closeable with the registry map. This should not do any
     * long running or potentially blocking operations as is is executed under the registry's lock.
     */
    protected abstract void doRegister(
            @Nonnull C closeable, @Nonnull Map<Closeable, T> closeableMap);

    /**
     * Does the actual un-registration of the closeable from the registry map. This should not do
     * any long running or potentially blocking operations as is is executed under the registry's
     * lock.
     */
    protected abstract boolean doUnRegister(
            @Nonnull C closeable, @Nonnull Map<Closeable, T> closeableMap);

    /**
     * Returns the lock on which manipulations to members closeableToRef and closeable must be
     * synchronized.
     */
    protected final Object getSynchronizationLock() {
        return lock;
    }

    /** Adds a mapping to the registry map, respecting locking. */
    protected final void addCloseableInternal(Closeable closeable, T metaData) {
        synchronized (getSynchronizationLock()) {
            closeableToRef.put(closeable, metaData);
        }
    }

    /** Removes a mapping from the registry map, respecting locking. */
    protected final boolean removeCloseableInternal(Closeable closeable) {
        synchronized (getSynchronizationLock()) {
            return closeableToRef.remove(closeable) != null;
        }
    }

    @VisibleForTesting
    public final int getNumberOfRegisteredCloseables() {
        synchronized (getSynchronizationLock()) {
            return closeableToRef.size();
        }
    }

    @VisibleForTesting
    public final boolean isCloseableRegistered(Closeable c) {
        synchronized (getSynchronizationLock()) {
            return closeableToRef.containsKey(c);
        }
    }
}