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.subscriptions;
/**
 * 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.
 */

import java.util.concurrent.atomic.*;

import org.reactivestreams.Subscription;

import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.util.BackpressureHelper;

Arbitrates requests and cancellation between Subscriptions.
/**
 * Arbitrates requests and cancellation between Subscriptions.
 */
public class SubscriptionArbiter extends AtomicInteger implements Subscription {

    private static final long serialVersionUID = -2189523197179400958L;

    
The current subscription which may null if no Subscriptions have been set.
/**
     * The current subscription which may null if no Subscriptions have been set.
     */
    Subscription actual;

    
The current outstanding request amount.
/**
     * The current outstanding request amount.
     */
    long requested;

    final AtomicReference<Subscription> missedSubscription;

    final AtomicLong missedRequested;

    final AtomicLong missedProduced;

    final boolean cancelOnReplace;

    volatile boolean cancelled;

    protected boolean unbounded;

    public SubscriptionArbiter(boolean cancelOnReplace) {
        this.cancelOnReplace = cancelOnReplace;
        missedSubscription = new AtomicReference<Subscription>();
        missedRequested = new AtomicLong();
        missedProduced = new AtomicLong();
    }

    
Atomically sets a new subscription.
Params:
s – the subscription to set, not null (verified)/**
     * Atomically sets a new subscription.
     * @param s the subscription to set, not null (verified)
     */
    public final void setSubscription(Subscription s) {
        if (cancelled) {
            s.cancel();
            return;
        }

        ObjectHelper.requireNonNull(s, "s is null");

        if (get() == 0 && compareAndSet(0, 1)) {
            Subscription a = actual;

            if (a != null && cancelOnReplace) {
                a.cancel();
            }

            actual = s;

            long r = requested;

            if (decrementAndGet() != 0) {
                drainLoop();
            }

            if (r != 0L) {
                s.request(r);
            }

            return;
        }

        Subscription a = missedSubscription.getAndSet(s);
        if (a != null && cancelOnReplace) {
            a.cancel();
        }
        drain();
    }

    @Override
    public final void request(long n) {
        if (SubscriptionHelper.validate(n)) {
            if (unbounded) {
                return;
            }
            if (get() == 0 && compareAndSet(0, 1)) {
                long r = requested;

                if (r != Long.MAX_VALUE) {
                    r = BackpressureHelper.addCap(r, n);
                    requested = r;
                    if (r == Long.MAX_VALUE) {
                        unbounded = true;
                    }
                }
                Subscription a = actual;

                if (decrementAndGet() != 0) {
                    drainLoop();
                }

                if (a != null) {
                    a.request(n);
                }

                return;
            }

            BackpressureHelper.add(missedRequested, n);

            drain();
        }
    }

    public final void produced(long n) {
        if (unbounded) {
            return;
        }
        if (get() == 0 && compareAndSet(0, 1)) {
            long r = requested;

            if (r != Long.MAX_VALUE) {
                long u = r - n;
                if (u < 0L) {
                    SubscriptionHelper.reportMoreProduced(u);
                    u = 0;
                }
                requested = u;
            }

            if (decrementAndGet() == 0) {
                return;
            }

            drainLoop();

            return;
        }

        BackpressureHelper.add(missedProduced, n);

        drain();
    }

    @Override
    public void cancel() {
        if (!cancelled) {
            cancelled = true;

            drain();
        }
    }

    final void drain() {
        if (getAndIncrement() != 0) {
            return;
        }
        drainLoop();
    }

    final void drainLoop() {
        int missed = 1;

        long requestAmount = 0L;
        Subscription requestTarget = null;

        for (; ; ) {

            Subscription ms = missedSubscription.get();

            if (ms != null) {
                ms = missedSubscription.getAndSet(null);
            }

            long mr = missedRequested.get();
            if (mr != 0L) {
                mr = missedRequested.getAndSet(0L);
            }

            long mp = missedProduced.get();
            if (mp != 0L) {
                mp = missedProduced.getAndSet(0L);
            }

            Subscription a = actual;

            if (cancelled) {
                if (a != null) {
                    a.cancel();
                    actual = null;
                }
                if (ms != null) {
                    ms.cancel();
                }
            } else {
                long r = requested;
                if (r != Long.MAX_VALUE) {
                    long u = BackpressureHelper.addCap(r, mr);

                    if (u != Long.MAX_VALUE) {
                        long v = u - mp;
                        if (v < 0L) {
                            SubscriptionHelper.reportMoreProduced(v);
                            v = 0;
                        }
                        r = v;
                    } else {
                        r = u;
                    }
                    requested = r;
                }

                if (ms != null) {
                    if (a != null && cancelOnReplace) {
                        a.cancel();
                    }
                    actual = ms;
                    if (r != 0L) {
                        requestAmount = BackpressureHelper.addCap(requestAmount, r);
                        requestTarget = ms;
                    }
                } else if (a != null && mr != 0L) {
                    requestAmount = BackpressureHelper.addCap(requestAmount, mr);
                    requestTarget = a;
                }
            }

            missed = addAndGet(-missed);
            if (missed == 0) {
                if (requestAmount != 0L) {
                    requestTarget.request(requestAmount);
                }
                return;
            }
        }
    }

    
Returns true if the arbiter runs in unbounded mode.
Returns:
true if the arbiter runs in unbounded mode/**
     * Returns true if the arbiter runs in unbounded mode.
     * @return true if the arbiter runs in unbounded mode
     */
    public final boolean isUnbounded() {
        return unbounded;
    }

    
Returns true if the arbiter has been cancelled.
Returns:
true if the arbiter has been cancelled/**
     * Returns true if the arbiter has been cancelled.
     * @return true if the arbiter has been cancelled
     */
    public final boolean isCancelled() {
        return cancelled;
    }
}