ratpack.reload.internal.ReloadableFileBackedFactory.java Source code

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Here is the source code for ratpack.reload.internal.ReloadableFileBackedFactory.java

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/*
 * 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 ratpack.reload.internal;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.UnpooledByteBufAllocator;
import ratpack.func.Factory;
import ratpack.util.internal.IoUtils;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.attribute.FileTime;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import static ratpack.util.Exceptions.uncheck;

public class ReloadableFileBackedFactory<T> implements Factory<T> {

    // Note: we are blocking for IO on the main thread here, but it only really impacts
    // reloadable mode so it's not worth the complication of jumping off the main thread

    private final Path file;
    private final boolean reloadable;
    private final Producer<T> producer;
    private final Releaser<T> releaser;

    private final AtomicReference<FileTime> lastModifiedHolder = new AtomicReference<>(null);
    private final AtomicReference<ByteBuf> contentHolder = new AtomicReference<>();
    private final AtomicReference<T> delegateHolder = new AtomicReference<>(null);
    private final Lock lock = new ReentrantLock();

    static public interface Producer<T> {
        T produce(Path file, ByteBuf bytes) throws Exception;
    }

    static public interface Releaser<T> {
        void release(T thing);
    }

    private static class NullReleaser<T> implements Releaser<T> {
        @Override
        public void release(T thing) {

        }
    }

    public ReloadableFileBackedFactory(Path file, boolean reloadable, Producer<T> producer) {
        this(file, reloadable, producer, new NullReleaser<>());
    }

    public ReloadableFileBackedFactory(Path file, boolean reloadable, Producer<T> producer, Releaser<T> releaser) {
        this.file = file;
        this.reloadable = reloadable;
        this.producer = producer;
        this.releaser = releaser;

        if (!reloadable) {
            try {
                refresh();
            } catch (Exception e) {
                throw uncheck(e);
            }
        }
    }

    public T create() {
        if (!reloadable) {
            return delegateHolder.get();
        }

        // If the file disappeared, wait a little for it to appear
        int i = 10;
        while (!Files.exists(file) && --i > 0) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                throw uncheck(e);
            }
        }

        if (!Files.exists(file)) {
            return null;
        }

        try {
            if (refreshNeeded()) {
                refresh();
            }
        } catch (Exception e) {
            throw uncheck(e);
        }

        return delegateHolder.get();
    }

    private boolean isBytesAreSame() throws IOException {
        lock.lock();
        try {
            ByteBuf existing = contentHolder.get();
            //noinspection SimplifiableIfStatement
            if (existing == null) {
                return false;
            }

            return IoUtils.read(UnpooledByteBufAllocator.DEFAULT, file).equals(existing);
        } finally {
            lock.unlock();
        }
    }

    private boolean refreshNeeded() throws IOException {
        return !Files.getLastModifiedTime(file).equals(lastModifiedHolder.get()) || !isBytesAreSame();
    }

    private void refresh() throws Exception {
        lock.lock();
        try {
            FileTime lastModifiedTime = Files.getLastModifiedTime(file);
            ByteBuf bytes = IoUtils.read(UnpooledByteBufAllocator.DEFAULT, file);

            if (lastModifiedTime.equals(lastModifiedHolder.get()) && bytes.equals(contentHolder.get())) {
                return;
            }

            T previous = delegateHolder.getAndSet(null);
            if (previous != null) {
                releaser.release(previous);
            }
            delegateHolder.set(producer.produce(file, bytes));

            this.lastModifiedHolder.set(lastModifiedTime);
            this.contentHolder.set(bytes);
        } finally {
            lock.unlock();
        }
    }

}