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 jdk.internal.net.http.common;

    27 

    28 import java.util.concurrent.atomic.AtomicLong;

    29 

    30 /**

    31  * Encapsulates operations with demand (Reactive Streams).

    32  *

    33  * <p> Demand is the aggregated number of elements requested by a Subscriber

    34  * which is yet to be delivered (fulfilled) by the Publisher.

    35  */

    36 public final class Demand {

    37 

    38     private final AtomicLong val = new AtomicLong();

    39 

    40     /**

    41      * Increases this demand by the specified positive value.

    42      *

    43      * @param n

    44      *         increment {@code > 0}

    45      *

    46      * @return {@code true} iff prior to this operation this demand was fulfilled

    47      */

    48     public boolean increase(long n) {

    49         if (n <= 0) {

    50             throw new IllegalArgumentException(String.valueOf(n));

    51         }

    52         long prev = val.getAndAccumulate(n, (p, i) -> p + i < 0 ? Long.MAX_VALUE : p + i);

    53         return prev == 0;

    54     }

    55 

    56     /**

    57      * Increases this demand by 1 but only if it is fulfilled.

    58      * @return true if the demand was increased, false otherwise.

    59      */

    60     public boolean increaseIfFulfilled() {

    61         return val.compareAndSet(0, 1);

    62     }

    63 

    64     /**

    65      * Tries to decrease this demand by the specified positive value.

    66      *

    67      * <p> The actual value this demand has been decreased by might be less than

    68      * {@code n}, including {@code 0} (no decrease at all).

    69      *

    70      * @param n

    71      *         decrement {@code > 0}

    72      *

    73      * @return a value {@code m} ({@code 0 <= m <= n}) this demand has been

    74      *         actually decreased by

    75      */

    76     public long decreaseAndGet(long n) {

    77         if (n <= 0) {

    78             throw new IllegalArgumentException(String.valueOf(n));

    79         }

    80         long p, d;

    81         do {

    82             d = val.get();

    83             p = Math.min(d, n);

    84         } while (!val.compareAndSet(d, d - p));

    85         return p;

    86     }

    87 

    88     /**

    89      * Tries to decrease this demand by {@code 1}.

    90      *

    91      * @return {@code true} iff this demand has been decreased by {@code 1}

    92      */

    93     public boolean tryDecrement() {

    94         return decreaseAndGet(1) == 1;

    95     }

    96 

    97     /**

    98      * @return {@code true} iff there is no unfulfilled demand

    99      */

   100     public boolean isFulfilled() {

   101         return val.get() == 0;

   102     }

   103 

   104     /**

   105      * Resets this object to its initial state.

   106      */

   107     public void reset() {

   108         val.set(0);

   109     }

   110 

   111     /**

   112      * Returns the current value of this demand.

   113      *

   114      * @return the current value of this demand

   115      */

   116     public long get() {

   117         return val.get();

   118     }

   119 

   120     @Override

   121     public String toString() {

   122         return String.valueOf(val.get());

   123     }

   124 }