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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.internal.net.http.common;

import java.util.concurrent.Flow;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Consumer;

Maintains subscription counter and provides primitives for:
- accessing window
- reducing window when delivering items externally
- resume delivery when window was zero previously
/**
 * Maintains subscription counter and provides primitives for:
 * - accessing window
 * - reducing window when delivering items externally
 * - resume delivery when window was zero previously
 */
public class SubscriptionBase implements Flow.Subscription {

    final Demand demand = new Demand();

    final SequentialScheduler scheduler; // when window was zero and is opened, run this
    final Runnable cancelAction; // when subscription cancelled, run this
    final AtomicBoolean cancelled;
    final Consumer<Throwable> onError;

    public SubscriptionBase(SequentialScheduler scheduler, Runnable cancelAction) {
        this(scheduler, cancelAction, null);
    }

    public SubscriptionBase(SequentialScheduler scheduler,
                            Runnable cancelAction,
                            Consumer<Throwable> onError) {
        this.scheduler = scheduler;
        this.cancelAction = cancelAction;
        this.cancelled = new AtomicBoolean(false);
        this.onError = onError;
    }

    @Override
    public void request(long n) {
        try {
            if (demand.increase(n))
                scheduler.runOrSchedule();
        } catch(Throwable t) {
            if (onError != null) {
                if (cancelled.getAndSet(true))
                    return;
                onError.accept(t);
            } else throw t;
        }
    }

    @Override
    public synchronized String toString() {
        return "SubscriptionBase: window = " + demand.get() +
                " cancelled = " + cancelled.toString();
    }

    
Returns true if the window was reduced by 1. In that case
items must be supplied to subscribers and the scheduler run
externally. If the window could not be reduced by 1, then false
is returned and the scheduler will run later when the window is updated.
/**
     * Returns true if the window was reduced by 1. In that case
     * items must be supplied to subscribers and the scheduler run
     * externally. If the window could not be reduced by 1, then false
     * is returned and the scheduler will run later when the window is updated.
     */
    public boolean tryDecrement() {
        return demand.tryDecrement();
    }

    public long window() {
        return demand.get();
    }

    @Override
    public void cancel() {
        if (cancelled.getAndSet(true))
            return;
        scheduler.stop();
        cancelAction.run();
    }
}