tmf/org.lttng.scope.tmf2.views.core/src/org/lttng/scope/tmf2/views/core/NestingBoolean.java

   1 /*
   2  * Copyright (C) 2017 EfficiOS Inc., Alexandre Montplaisir <alexmonthy@efficios.com>
   3  *
   4  * All rights reserved. This program and the accompanying materials are
   5  * made available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  */
   9
  10 package org.lttng.scope.tmf2.views.core;
  11
  12 import java.util.concurrent.atomic.AtomicInteger;
  13
  14 import javafx.beans.property.BooleanProperty;
  15 import javafx.beans.property.ReadOnlyBooleanProperty;
  16 import javafx.beans.property.SimpleBooleanProperty;
  17 import javafx.beans.value.ChangeListener;
  18
  19 /**
  20  * Utility class that serves as a wrapper around a single boolean flag that can
  21  * be enabled/disabled. It counts the number of times {@link #disable()} is
  22  * called, and only really re-enables the inner value when {@link #enable()} is
  23  * called that many times.
  24  *
  25  * It is meant to be useful in multi-thread scenarios, where concurrent
  26  * "critical sections" may want to disable something like a listener, and not
  27  * have it really be re-enabled until all critical sections are finished. Thus
  28  * it is thread-safe.
  29  *
  30  * The inner value is exposed through the {@link #enabledProperty()} method, which
  31  * returns a {@link ReadOnlyBooleanProperty}. You can attach
  32  * {@link ChangeListener}s to that property to get notified of inner value
  33  * changes.
  34  *
  35  * It is "enabled" at creation time.
  36  *
  37  * @author Alexandre Montplaisir
  38  */
  39 public class NestingBoolean {
  40
  41     private final AtomicInteger fDisabledCount = new AtomicInteger(0);
  42     private final BooleanProperty fBoolean = new SimpleBooleanProperty(true);
  43
  44     /**
  45      * Decrease the "disabled" count by 1. If it reaches (or already was at) 0
  46      * then the value is truly enabled.
  47      */
  48     public synchronized void enable() {
  49         /* Decrement the count but only if it is currently above 0 */
  50         int ret = fDisabledCount.updateAndGet(value -> value > 0 ? value - 1 : 0);
  51         if (ret == 0) {
  52             fBoolean.set(true);
  53         }
  54     }
  55
  56     /**
  57      * Increase the "disabled" count by 1. The inner value will necessarily be
  58      * disabled after this call.
  59      */
  60     public synchronized void disable() {
  61         fDisabledCount.incrementAndGet();
  62         fBoolean.set(false);
  63     }
  64
  65     /**
  66      * Property representing the inner boolean value.
  67      *
  68      * @return The inner value
  69      */
  70     public ReadOnlyBooleanProperty enabledProperty() {
  71         return fBoolean;
  72     }
  73 }