text: /*
   *  Copyright (C) 2015 Igalia S.L
   *
   *  This library is free software; you can redistribute it and/or
   *  modify it under the terms of the GNU Lesser General Public
   *  License as published by the Free Software Foundation; either
   *  version 2 of the License, or (at your option) any later version.
   *
   *  This library is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   *  Lesser General Public License for more details.
   *
   *  You should have received a copy of the GNU Lesser General Public
   *  License along with this library; if not, write to the Free Software
   *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
   */
  
  #pragma once
  
  #include <functional>
  #include <wtf/Atomics.h>
  #include <wtf/Lock.h>
  #include <wtf/MainThread.h>
  #include <wtf/RunLoop.h>
  #include <wtf/ThreadSafeRefCounted.h>
  
  namespace WebCore {
  
  template <typename T>
  class MainThreadNotifier final : public ThreadSafeRefCounted<MainThreadNotifier<T>> {
  public:
      static Ref<MainThreadNotifier> create()
      {
          return adoptRef(*new MainThreadNotifier());
      }
  
      ~MainThreadNotifier()
      {
          ASSERT(!m_isValid.load());
      }
  
      bool isValid() const { return m_isValid.load(); }
  
      template<typename F>
      void notify(T notificationType, F&& callbackFunctor)
      {
          ASSERT(m_isValid.load());
          // Assert that there is only one bit on at a time.
          ASSERT(!(static_cast<int>(notificationType) & (static_cast<int>(notificationType) - 1)));
          if (isMainThread()) {
              removePendingNotification(notificationType);
              callbackFunctor();
              return;
          }
  
          if (!addPendingNotification(notificationType))
              return;
  
          RunLoop::main().dispatch([this, protectedThis = makeRef(*this), notificationType, callback = WTF::Function<void()>(WTFMove(callbackFunctor))] {
              if (!m_isValid.load())
                  return;
              if (removePendingNotification(notificationType))
                  callback();
          });
      }
  
      template<typename F>
      void notifyAndWait(T notificationType, F&& callbackFunctor)
      {
          Lock mutex;
          Condition condition;
  
          notify(notificationType, [functor = WTFMove(callbackFunctor), &condition, &mutex] {
              functor();
              LockHolder holder(mutex);
              condition.notifyOne();
          });
  
          if (!isMainThread()) {
              LockHolder holder(mutex);
              condition.wait(mutex);
          }
      }
  
      void cancelPendingNotifications(unsigned mask = 0)
      {
          ASSERT(m_isValid.load());
          LockHolder locker(m_pendingNotificationsLock);
          if (mask)
              m_pendingNotifications &= ~mask;
          else
              m_pendingNotifications = 0;
      }
  
      void invalidate()
      {
          ASSERT(m_isValid.load());
          m_isValid.store(false);
      }
  
  private:
      MainThreadNotifier()
      {
          m_isValid.store(true);
      }
  
      bool addPendingNotification(T notificationType)
      {
          LockHolder locker(m_pendingNotificationsLock);
          if (notificationType & m_pendingNotifications)
              return false;
          m_pendingNotifications |= notificationType;
          return true;
      }
  
      bool removePendingNotification(T notificationType)
      {
          LockHolder locker(m_pendingNotificationsLock);
          if (notificationType & m_pendingNotifications) {
              m_pendingNotifications &= ~notificationType;
              return true;
          }
          return false;
      }
  
      Lock m_pendingNotificationsLock;
      unsigned m_pendingNotifications { 0 };
      Atomic<bool> m_isValid;
  };
  
  } // namespace WebCore
  
  