1 /*
   2  * Copyright (c) 2016, 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 jdk.internal.net.http;
  27 
  28 import java.util.Iterator;
  29 import java.util.concurrent.Flow;
  30 import jdk.internal.net.http.common.Demand;
  31 import jdk.internal.net.http.common.SequentialScheduler;
  32 
  33 /**
  34  * A Publisher that publishes items obtained from the given Iterable. Each new
  35  * subscription gets a new Iterator.
  36  */
  37 class PullPublisher<T> implements Flow.Publisher<T> {
  38 
  39     // Only one of `iterable` and `throwable` can be non-null. throwable is
  40     // non-null when an error has been encountered, by the creator of
  41     // PullPublisher, while subscribing the subscriber, but before subscribe has
  42     // completed.
  43     private final Iterable<T> iterable;
  44     private final Throwable throwable;
  45 
  46     PullPublisher(Iterable<T> iterable, Throwable throwable) {
  47         this.iterable = iterable;
  48         this.throwable = throwable;
  49     }
  50 
  51     PullPublisher(Iterable<T> iterable) {
  52         this(iterable, null);
  53     }
  54 
  55     @Override
  56     public void subscribe(Flow.Subscriber<? super T> subscriber) {
  57         Subscription sub;
  58         if (throwable != null) {
  59             assert iterable == null : "non-null iterable: " + iterable;
  60             sub = new Subscription(subscriber, null, throwable);
  61         } else {
  62             assert throwable == null : "non-null exception: " + throwable;
  63             sub = new Subscription(subscriber, iterable.iterator(), null);
  64         }
  65         subscriber.onSubscribe(sub);
  66 
  67         if (throwable != null) {
  68             sub.pullScheduler.runOrSchedule();
  69         }
  70     }
  71 
  72     private class Subscription implements Flow.Subscription {
  73 
  74         private final Flow.Subscriber<? super T> subscriber;
  75         private final Iterator<T> iter;
  76         private volatile boolean completed;
  77         private volatile boolean cancelled;
  78         private volatile Throwable error;
  79         final SequentialScheduler pullScheduler = new SequentialScheduler(new PullTask());
  80         private final Demand demand = new Demand();
  81 
  82         Subscription(Flow.Subscriber<? super T> subscriber,
  83                      Iterator<T> iter,
  84                      Throwable throwable) {
  85             this.subscriber = subscriber;
  86             this.iter = iter;
  87             this.error = throwable;
  88         }
  89 
  90         final class PullTask extends SequentialScheduler.CompleteRestartableTask {
  91             @Override
  92             protected void run() {
  93                 if (completed || cancelled) {
  94                     return;
  95                 }
  96 
  97                 Throwable t = error;
  98                 if (t != null) {
  99                     completed = true;
 100                     pullScheduler.stop();
 101                     subscriber.onError(t);
 102                     return;
 103                 }
 104 
 105                 while (demand.tryDecrement() && !cancelled) {
 106                     if (!iter.hasNext()) {
 107                         break;
 108                     } else {
 109                         subscriber.onNext(iter.next());
 110                     }
 111                 }
 112                 if (!iter.hasNext() && !cancelled) {
 113                     completed = true;
 114                     pullScheduler.stop();
 115                     subscriber.onComplete();
 116                 }
 117             }
 118         }
 119 
 120         @Override
 121         public void request(long n) {
 122             if (cancelled)
 123                 return;  // no-op
 124 
 125             if (n <= 0) {
 126                 error = new IllegalArgumentException("illegal non-positive request:" + n);
 127             } else {
 128                 demand.increase(n);
 129             }
 130             pullScheduler.runOrSchedule();
 131         }
 132 
 133         @Override
 134         public void cancel() {
 135             cancelled = true;
 136         }
 137     }
 138 }