Copyright (c) 2016-present, RxJava Contributors.
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.
/**
 * Copyright (c) 2016-present, RxJava Contributors.
 * 
 * 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 io.reactivex.internal.schedulers;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicReference;

import io.reactivex.disposables.Disposable;
import io.reactivex.internal.functions.Functions;
import io.reactivex.plugins.RxJavaPlugins;

Wrapper for a regular task that gets immediately rescheduled when the task completed.
/**
 * Wrapper for a regular task that gets immediately rescheduled when the task completed.
 */
final class InstantPeriodicTask implements Callable<Void>, Disposable {

    final Runnable task;

    final AtomicReference<Future<?>> rest;

    final AtomicReference<Future<?>> first;

    final ExecutorService executor;

    Thread runner;

    static final FutureTask<Void> CANCELLED = new FutureTask<Void>(Functions.EMPTY_RUNNABLE, null);

    InstantPeriodicTask(Runnable task, ExecutorService executor) {
        super();
        this.task = task;
        this.first = new AtomicReference<Future<?>>();
        this.rest = new AtomicReference<Future<?>>();
        this.executor = executor;
    }

    @Override
    public Void call() throws Exception {
        runner = Thread.currentThread();
        try {
            task.run();
            setRest(executor.submit(this));
            runner = null;
        } catch (Throwable ex) {
            runner = null;
            RxJavaPlugins.onError(ex);
        }
        return null;
    }

    @Override
    public void dispose() {
        Future<?> current = first.getAndSet(CANCELLED);
        if (current != null && current != CANCELLED) {
            current.cancel(runner != Thread.currentThread());
        }
        current = rest.getAndSet(CANCELLED);
        if (current != null && current != CANCELLED) {
            current.cancel(runner != Thread.currentThread());
        }
    }

    @Override
    public boolean isDisposed() {
        return first.get() == CANCELLED;
    }

    void setFirst(Future<?> f) {
        for (;;) {
            Future<?> current = first.get();
            if (current == CANCELLED) {
                f.cancel(runner != Thread.currentThread());
                return;
            }
            if (first.compareAndSet(current, f)) {
                return;
            }
        }
    }

    void setRest(Future<?> f) {
        for (;;) {
            Future<?> current = rest.get();
            if (current == CANCELLED) {
                f.cancel(runner != Thread.currentThread());
                return;
            }
            if (rest.compareAndSet(current, f)) {
                return;
            }
        }
    }
}