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Reactive Extensions for Java
There is a newer version: 3.1.9
/*
 * 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.rxjava3.internal.schedulers;

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

import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.internal.functions.Functions;
import io.reactivex.rxjava3.plugins.RxJavaPlugins;

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

    final Runnable task;

    final AtomicReference> rest;

    final AtomicReference> first;

    final ExecutorService executor;

    Thread runner;

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

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

    @Override
    public Void call() {
        runner = Thread.currentThread();
        try {
            task.run();
            runner = null;
            setRest(executor.submit(this));
        } catch (Throwable ex) {
            // Exceptions.throwIfFatal(ex); nowhere to go
            runner = null;
            RxJavaPlugins.onError(ex);
            throw 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;
            }
        }
    }
}