1 /*
   2  * Copyright (c) 2015, 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.websocket;
  27 
  28 import java.io.IOException;
  29 import java.nio.channels.SelectionKey;
  30 import java.util.concurrent.atomic.AtomicBoolean;
  31 import java.util.function.Consumer;
  32 
  33 import static java.util.Objects.requireNonNull;
  34 
  35 /*
  36  * Sends messages one at a time, in an asynchronous and non-blocking fashion.
  37  *
  38  * No matter whether the message has been fully sent or an error has occurred,
  39  * the transmitter reports the outcome to the supplied handler and becomes ready
  40  * to accept a new message. Until then, the transmitter is considered "busy" and
  41  * an IllegalStateException will be thrown on each attempt to invoke send.
  42  */
  43 final class Transmitter {
  44 
  45     /* This flag is used solely for assertions */
  46     private final AtomicBoolean busy = new AtomicBoolean();
  47     private OutgoingMessage message;
  48     private Consumer<Exception> completionHandler;
  49     private final RawChannel channel;
  50     private final RawChannel.RawEvent event;
  51 
  52     Transmitter(RawChannel channel) {
  53         this.channel = requireNonNull(channel);
  54         this.event = createHandler();
  55     }
  56 
  57     /**
  58      * The supplied handler may be invoked in the calling thread.
  59      * A {@code StackOverflowError} may thus occur if there's a possibility
  60      * that this method is called again by the supplied handler.
  61      */
  62     void send(OutgoingMessage message, Consumer<Exception> completionHandler) {
  63         requireNonNull(message);
  64         requireNonNull(completionHandler);
  65         if (!busy.compareAndSet(false, true)) {
  66             throw new IllegalStateException();
  67         }
  68         send0(message, completionHandler);
  69     }
  70 
  71     private RawChannel.RawEvent createHandler() {
  72         return new RawChannel.RawEvent() {
  73 
  74             @Override
  75             public int interestOps() {
  76                 return SelectionKey.OP_WRITE;
  77             }
  78 
  79             @Override
  80             public void handle() {
  81                 // registerEvent(e) happens-before subsequent e.handle(), so
  82                 // we're fine reading the stored message and the completionHandler
  83                 send0(message, completionHandler);
  84             }
  85         };
  86     }
  87 
  88     private void send0(OutgoingMessage message, Consumer<Exception> handler) {
  89         boolean b = busy.get();
  90         assert b; // Please don't inline this, as busy.get() has memory
  91                   // visibility effects and we don't want the program behaviour
  92                   // to depend on whether the assertions are turned on
  93                   // or turned off
  94         try {
  95             boolean sent = message.sendTo(channel);
  96             if (sent) {
  97                 busy.set(false);
  98                 handler.accept(null);
  99             } else {
 100                 // The message has not been fully sent, the transmitter needs to
 101                 // remember the message until it can continue with sending it
 102                 this.message = message;
 103                 this.completionHandler = handler;
 104                 try {
 105                     channel.registerEvent(event);
 106                 } catch (IOException e) {
 107                     this.message = null;
 108                     this.completionHandler = null;
 109                     busy.set(false);
 110                     handler.accept(e);
 111                 }
 112             }
 113         } catch (IOException e) {
 114             busy.set(false);
 115             handler.accept(e);
 116         }
 117     }
 118 }