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       1             : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
       3             : /* This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : #ifndef nsEventQueue_h__
       8             : #define nsEventQueue_h__
       9             : 
      10             : #include <stdlib.h>
      11             : #include "mozilla/CondVar.h"
      12             : #include "mozilla/Mutex.h"
      13             : #include "nsIRunnable.h"
      14             : #include "nsCOMPtr.h"
      15             : #include "mozilla/AlreadyAddRefed.h"
      16             : #include "mozilla/UniquePtr.h"
      17             : 
      18             : class nsThreadPool;
      19             : 
      20             : // A threadsafe FIFO event queue...
      21             : class nsEventQueue
      22             : {
      23             : public:
      24             :   typedef mozilla::MutexAutoLock MutexAutoLock;
      25             : 
      26             :   enum EventQueueType
      27             :   {
      28             :     eNormalQueue,
      29             :     eSharedCondVarQueue
      30             :   };
      31             : 
      32             :   nsEventQueue(mozilla::CondVar& aCondVar, EventQueueType aType);
      33             :   ~nsEventQueue();
      34             : 
      35             :   // This method adds a new event to the pending event queue.  The queue holds
      36             :   // a strong reference to the event after this method returns.  This method
      37             :   // cannot fail.
      38             :   void PutEvent(nsIRunnable* aEvent, MutexAutoLock& aProofOfLock);
      39             :   void PutEvent(already_AddRefed<nsIRunnable>&& aEvent,
      40             :                 MutexAutoLock& aProofOfLock);
      41             : 
      42             :   // Return the first event in the queue without popping it. Returns whether the
      43             :   // queue was empty or not. aEvent is set to null if the queue was empty.
      44             :   bool PeekEvent(nsIRunnable** aEvent, MutexAutoLock& aProofOfLock);
      45             : 
      46             :   // This method gets an event from the event queue.  If mayWait is true, then
      47             :   // the method will block the calling thread until an event is available.  If
      48             :   // the event is null, then the method returns immediately indicating whether
      49             :   // or not an event is pending.  When the resulting event is non-null, the
      50             :   // caller is responsible for releasing the event object.  This method does
      51             :   // not alter the reference count of the resulting event.
      52             :   bool GetEvent(bool aMayWait, nsIRunnable** aEvent,
      53             :                 MutexAutoLock& aProofOfLock);
      54             : 
      55             :   // This method returns true if there is a pending event.
      56        4825 :   bool HasPendingEvent(MutexAutoLock& aProofOfLock)
      57             :   {
      58        4825 :     return GetEvent(false, nullptr, aProofOfLock);
      59             :   }
      60             : 
      61             :   // This method returns the next pending event or null.
      62         159 :   bool GetPendingEvent(nsIRunnable** aRunnable, MutexAutoLock& aProofOfLock)
      63             :   {
      64         159 :     return GetEvent(false, aRunnable, aProofOfLock);
      65             :   }
      66             : 
      67             :   size_t Count(MutexAutoLock&) const;
      68             : 
      69             : private:
      70        7205 :   bool IsEmpty()
      71             :   {
      72        7205 :     return !mHead || (mHead == mTail && mOffsetHead == mOffsetTail);
      73             :   }
      74             : 
      75             :   enum
      76             :   {
      77             :     EVENTS_PER_PAGE = 255
      78             :   };
      79             : 
      80             :   // Page objects are linked together to form a simple deque.
      81             : 
      82             :   struct Page
      83             :   {
      84             :     struct Page* mNext;
      85             :     nsIRunnable* mEvents[EVENTS_PER_PAGE];
      86             :   };
      87             : 
      88             :   static_assert((sizeof(Page) & (sizeof(Page) - 1)) == 0,
      89             :                 "sizeof(Page) should be a power of two to avoid heap slop.");
      90             : 
      91          87 :   static Page* NewPage()
      92             :   {
      93          87 :     return static_cast<Page*>(moz_xcalloc(1, sizeof(Page)));
      94             :   }
      95             : 
      96          17 :   static void FreePage(Page* aPage)
      97             :   {
      98          17 :     free(aPage);
      99          17 :   }
     100             : 
     101             :   Page* mHead;
     102             :   Page* mTail;
     103             : 
     104             :   uint16_t mOffsetHead;  // offset into mHead where next item is removed
     105             :   uint16_t mOffsetTail;  // offset into mTail where next item is added
     106             :   mozilla::CondVar& mEventsAvailable;
     107             : 
     108             :   EventQueueType mType;
     109             : 
     110             :   // These methods are made available to nsThreadPool as a hack, since
     111             :   // nsThreadPool needs to have its threads sleep for fixed amounts of
     112             :   // time as well as being able to wake up all threads when thread
     113             :   // limits change.
     114             :   friend class nsThreadPool;
     115          73 :   void Wait(PRIntervalTime aInterval)
     116             :   {
     117          73 :     MOZ_ASSERT(mType == eNormalQueue);
     118          73 :     mEventsAvailable.Wait(aInterval);
     119          71 :   }
     120           0 :   void NotifyAll()
     121             :   {
     122           0 :     MOZ_ASSERT(mType == eNormalQueue);
     123           0 :     mEventsAvailable.NotifyAll();
     124           0 :   }
     125             : };
     126             : 
     127             : #endif  // nsEventQueue_h__