1 /*

     2  * Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.net.http.internal.common;

    27 

    28 import java.util.concurrent.Flow;

    29 import java.util.concurrent.atomic.AtomicBoolean;

    30 

    31 /**

    32  * Maintains subscription counter and provides primitives for

    33  * - accessing window

    34  * - reducing window when delivering items externally

    35  * - resume delivery when window was zero previously

    36  *

    37  * @author mimcmah

    38  */

    39 public class SubscriptionBase implements Flow.Subscription {

    40 

    41     final Demand demand = new Demand();

    42 

    43     final SequentialScheduler scheduler; // when window was zero and is opened, run this

    44     final Runnable cancelAction; // when subscription cancelled, run this

    45     final AtomicBoolean cancelled;

    46 

    47     public SubscriptionBase(SequentialScheduler scheduler, Runnable cancelAction) {

    48         this.scheduler = scheduler;

    49         this.cancelAction = cancelAction;

    50         this.cancelled = new AtomicBoolean(false);

    51     }

    52 

    53     @Override

    54     public void request(long n) {

    55         if (demand.increase(n))

    56             scheduler.runOrSchedule();

    57     }

    58 

    59 

    60 

    61     @Override

    62     public synchronized String toString() {

    63         return "SubscriptionBase: window = " + demand.get() +

    64                 " cancelled = " + cancelled.toString();

    65     }

    66 

    67     /**

    68      * Returns true if the window was reduced by 1. In that case

    69      * items must be supplied to subscribers and the scheduler run

    70      * externally. If the window could not be reduced by 1, then false

    71      * is returned and the scheduler will run later when the window is updated.

    72      */

    73     public boolean tryDecrement() {

    74         return demand.tryDecrement();

    75     }

    76 

    77     public long window() {

    78         return demand.get();

    79     }

    80 

    81     @Override

    82     public void cancel() {

    83         if (cancelled.getAndSet(true))

    84             return;

    85         scheduler.stop();

    86         cancelAction.run();

    87     }

    88 }