1 /*
   2  * Copyright (c) 2017, 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 jdk.incubator.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 }