michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim:set ts=2 sw=2 sts=2 et cindent: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef nsEventQueue_h__
michael@0: #define nsEventQueue_h__
michael@0: 
michael@0: #include <stdlib.h>
michael@0: #include "mozilla/ReentrantMonitor.h"
michael@0: #include "nsIRunnable.h"
michael@0: 
michael@0: // A threadsafe FIFO event queue...
michael@0: class nsEventQueue
michael@0: {
michael@0:   typedef mozilla::ReentrantMonitor ReentrantMonitor;
michael@0: 
michael@0: public:
michael@0:   nsEventQueue();
michael@0:   ~nsEventQueue();
michael@0: 
michael@0:   // This method adds a new event to the pending event queue.  The event object
michael@0:   // is AddRef'd if this method succeeds.  This method returns true if the
michael@0:   // event was stored in the event queue, and it returns false if it could
michael@0:   // not allocate sufficient memory.
michael@0:   bool PutEvent(nsIRunnable *event);
michael@0: 
michael@0:   // This method gets an event from the event queue.  If mayWait is true, then
michael@0:   // the method will block the calling thread until an event is available.  If
michael@0:   // the event is null, then the method returns immediately indicating whether
michael@0:   // or not an event is pending.  When the resulting event is non-null, the
michael@0:   // caller is responsible for releasing the event object.  This method does
michael@0:   // not alter the reference count of the resulting event.
michael@0:   bool GetEvent(bool mayWait, nsIRunnable **event);
michael@0: 
michael@0:   // This method returns true if there is a pending event.
michael@0:   bool HasPendingEvent() {
michael@0:     return GetEvent(false, nullptr);
michael@0:   }
michael@0: 
michael@0:   // This method returns the next pending event or null.
michael@0:   bool GetPendingEvent(nsIRunnable **runnable) {
michael@0:     return GetEvent(false, runnable);
michael@0:   }
michael@0: 
michael@0:   // This method waits for and returns the next pending event.
michael@0:   bool WaitPendingEvent(nsIRunnable **runnable) {
michael@0:     return GetEvent(true, runnable);
michael@0:   }
michael@0: 
michael@0:   // Expose the event queue's monitor for "power users"
michael@0:   ReentrantMonitor& GetReentrantMonitor() {
michael@0:     return mReentrantMonitor;
michael@0:   }
michael@0: 
michael@0: private:
michael@0: 
michael@0:   bool IsEmpty() {
michael@0:     return !mHead || (mHead == mTail && mOffsetHead == mOffsetTail);
michael@0:   }
michael@0: 
michael@0:   enum { EVENTS_PER_PAGE = 255 };
michael@0: 
michael@0:   // Page objects are linked together to form a simple deque.
michael@0: 
michael@0:   struct Page {
michael@0:     struct Page *mNext;
michael@0:     nsIRunnable *mEvents[EVENTS_PER_PAGE];
michael@0:   };
michael@0: 
michael@0:   static_assert((sizeof(Page) & (sizeof(Page) - 1)) == 0,
michael@0:                 "sizeof(Page) should be a power of two to avoid heap slop.");
michael@0: 
michael@0:   static Page *NewPage() {
michael@0:     return static_cast<Page *>(calloc(1, sizeof(Page)));
michael@0:   }
michael@0: 
michael@0:   static void FreePage(Page *p) {
michael@0:     free(p);
michael@0:   }
michael@0: 
michael@0:   ReentrantMonitor mReentrantMonitor;
michael@0: 
michael@0:   Page *mHead;
michael@0:   Page *mTail;
michael@0: 
michael@0:   uint16_t mOffsetHead;  // offset into mHead where next item is removed
michael@0:   uint16_t mOffsetTail;  // offset into mTail where next item is added
michael@0: };
michael@0: 
michael@0: #endif  // nsEventQueue_h__