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 * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
 * 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.
 *
 * 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.
 *
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 */

package org.reactivestreams;

/**
 * A {@link Subscription} represents a one-to-one lifecycle of a {@link Subscriber} subscribing to a {@link Publisher}.
 * <p>
 * It can only be used once by a single {@link Subscriber}.
 * <p>
 * It is used to both signal desire for data and cancel demand (and allow resource cleanup).
 *
 */
public interface Subscription {
    /**
     * No events will be sent by a {@link Publisher} until demand is signaled via this method.
     * <p>
     *  It can be called however often and whenever needed—but if the outstanding cumulative demand ever becomes Long.MAX_VALUE or more,
     *  it may be treated by the {@link Publisher} as "effectively unbounded".
     * <p>
     * Whatever has been requested can be sent by the {@link Publisher} so only signal demand for what can be safely handled.
     * <p>
     * A {@link Publisher} can send less than is requested if the stream ends but
     * then must emit either {@link Subscriber#onError(Throwable)} or {@link Subscriber#onComplete()}.
     *
     * @param n the strictly positive number of elements to requests to the upstream {@link Publisher}
     */
    public void request(long n);

    /**
     * Request the {@link Publisher} to stop sending data and clean up resources.
     * <p>
     * Data may still be sent to meet previously signalled demand after calling cancel.
     */
    public void cancel();
}