juce/source/src/events/juce_AsyncUpdater.cpp

   1 /*
   2   ==============================================================================
   3
   4    This file is part of the JUCE library - "Jules' Utility Class Extensions"
   5    Copyright 2004-11 by Raw Material Software Ltd.
   6
   7   ------------------------------------------------------------------------------
   8
   9    JUCE can be redistributed and/or modified under the terms of the GNU General
  10    Public License (Version 2), as published by the Free Software Foundation.
  11    A copy of the license is included in the JUCE distribution, or can be found
  12    online at www.gnu.org/licenses.
  13
  14    JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
  15    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  16    A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  17
  18   ------------------------------------------------------------------------------
  19
  20    To release a closed-source product which uses JUCE, commercial licenses are
  21    available: visit www.rawmaterialsoftware.com/juce for more information.
  22
  23   ==============================================================================
  24 */
  25
  26 #include "../core/juce_StandardHeader.h"
  27
  28 BEGIN_JUCE_NAMESPACE
  29
  30 #include "juce_AsyncUpdater.h"
  31 #include "juce_CallbackMessage.h"
  32 #include "juce_MessageManager.h"
  33
  34
  35 //==============================================================================
  36 class AsyncUpdaterMessage  : public CallbackMessage
  37 {
  38 public:
  39     AsyncUpdaterMessage (AsyncUpdater& owner_)
  40         : owner (owner_)
  41     {
  42     }
  43
  44     void messageCallback()
  45     {
  46         if (shouldDeliver.compareAndSetBool (0, 1))
  47             owner.handleAsyncUpdate();
  48     }
  49
  50     Atomic<int> shouldDeliver;
  51
  52 private:
  53     AsyncUpdater& owner;
  54 };
  55
  56 //==============================================================================
  57 AsyncUpdater::AsyncUpdater()
  58 {
  59     message = new AsyncUpdaterMessage (*this);
  60 }
  61
  62 inline Atomic<int>& AsyncUpdater::getDeliveryFlag() const noexcept
  63 {
  64     return static_cast <AsyncUpdaterMessage*> (message.getObject())->shouldDeliver;
  65 }
  66
  67 AsyncUpdater::~AsyncUpdater()
  68 {
  69     // You're deleting this object with a background thread while there's an update
  70     // pending on the main event thread - that's pretty dodgy threading, as the callback could
  71     // happen after this destructor has finished. You should either use a MessageManagerLock while
  72     // deleting this object, or find some other way to avoid such a race condition.
  73     jassert ((! isUpdatePending()) || MessageManager::getInstance()->currentThreadHasLockedMessageManager());
  74
  75     getDeliveryFlag().set (0);
  76 }
  77
  78 void AsyncUpdater::triggerAsyncUpdate()
  79 {
  80     if (getDeliveryFlag().compareAndSetBool (1, 0))
  81         message->post();
  82 }
  83
  84 void AsyncUpdater::cancelPendingUpdate() noexcept
  85 {
  86     getDeliveryFlag().set (0);
  87 }
  88
  89 void AsyncUpdater::handleUpdateNowIfNeeded()
  90 {
  91     // This can only be called by the event thread.
  92     jassert (MessageManager::getInstance()->currentThreadHasLockedMessageManager());
  93
  94     if (getDeliveryFlag().exchange (0) != 0)
  95         handleAsyncUpdate();
  96 }
  97
  98 bool AsyncUpdater::isUpdatePending() const noexcept
  99 {
 100     return getDeliveryFlag().value != 0;
 101 }
 102
 103
 104 END_JUCE_NAMESPACE