xbmc/threads/Event.cpp

   1 /*
   2  *  Copyright (c) 2002 Frodo
   3  *      Portions Copyright (c) by the authors of ffmpeg and xvid
   4  *  Copyright (C) 2002-2018 Team Kodi
   5  *  This file is part of Kodi - https://kodi.tv
   6  *
   7  *  SPDX-License-Identifier: GPL-2.0-or-later
   8  *  See LICENSES/README.md for more information.
   9  */
  10
  11 #include "Event.h"
  12
  13 #include <algorithm>
  14 #include <limits>
  15 #include <memory>
  16 #include <mutex>
  17
  18 using namespace std::chrono_literals;
  19
  20 void CEvent::addGroup(XbmcThreads::CEventGroup* group)
  21 {
  22   std::unique_lock<CCriticalSection> lock(groupListMutex);
  23   if (!groups)
  24     groups = std::make_unique<std::vector<XbmcThreads::CEventGroup*>>();
  25
  26   groups->push_back(group);
  27 }
  28
  29 void CEvent::removeGroup(XbmcThreads::CEventGroup* group)
  30 {
  31   std::unique_lock<CCriticalSection> lock(groupListMutex);
  32   if (groups)
  33   {
  34     groups->erase(std::remove(groups->begin(), groups->end(), group), groups->end());
  35     if (groups->empty())
  36     {
  37       groups.reset();
  38     }
  39   }
  40 }
  41
  42 // locking is ALWAYS done in this order:
  43 //  CEvent::groupListMutex -> CEventGroup::mutex -> CEvent::mutex
  44 void CEvent::Set()
  45 {
  46   // Originally I had this without locking. Thanks to FernetMenta who
  47   // pointed out that this creates a race condition between setting
  48   // checking the signal and calling wait() on the Wait call in the
  49   // CEvent class. This now perfectly matches the boost example here:
  50   // http://www.boost.org/doc/libs/1_41_0/doc/html/thread/synchronization.html#thread.synchronization.condvar_ref
  51   {
  52     std::unique_lock<CCriticalSection> slock(mutex);
  53     signaled = true;
  54   }
  55
  56   actualCv.notifyAll();
  57
  58   std::unique_lock<CCriticalSection> l(groupListMutex);
  59   if (groups)
  60   {
  61     for (auto* group : *groups)
  62       group->Set(this);
  63   }
  64 }
  65
  66 namespace XbmcThreads
  67 {
  68   /**
  69    * This will block until any one of the CEvents in the group are
  70    * signaled at which point a pointer to that CEvents will be
  71    * returned.
  72    */
  73   CEvent* CEventGroup::wait()
  74   {
  75     return wait(std::chrono::milliseconds::max());
  76   }
  77
  78   CEventGroup::CEventGroup(std::initializer_list<CEvent*> eventsList)
  79   : events{eventsList}
  80   {
  81     // we preping for a wait, so we need to set the group value on
  82     // all of the CEvents.
  83     for (auto* event : events)
  84     {
  85       event->addGroup(this);
  86     }
  87   }
  88
  89   CEventGroup::~CEventGroup()
  90   {
  91     for (auto* event : events)
  92     {
  93       event->removeGroup(this);
  94     }
  95   }
  96 }