xpcom/threads/nsEventQueue.h

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   3 /* ***** BEGIN LICENSE BLOCK *****
   4  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   5  *
   6  * The contents of this file are subject to the Mozilla Public License Version
   7  * 1.1 (the "License"); you may not use this file except in compliance with
   8  * the License. You may obtain a copy of the License at
   9  * http://www.mozilla.org/MPL/
  10  *
  11  * Software distributed under the License is distributed on an "AS IS" basis,
  12  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  13  * for the specific language governing rights and limitations under the
  14  * License.
  15  *
  16  * The Original Code is Mozilla code.
  17  *
  18  * The Initial Developer of the Original Code is Google Inc.
  19  * Portions created by the Initial Developer are Copyright (C) 2006
  20  * the Initial Developer. All Rights Reserved.
  21  *
  22  * Contributor(s):
  23  *  Darin Fisher <darin@meer.net>
  24  *
  25  * Alternatively, the contents of this file may be used under the terms of
  26  * either the GNU General Public License Version 2 or later (the "GPL"), or
  27  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  28  * in which case the provisions of the GPL or the LGPL are applicable instead
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  34  * the provisions above, a recipient may use your version of this file under
  35  * the terms of any one of the MPL, the GPL or the LGPL.
  36  *
  37  * ***** END LICENSE BLOCK ***** */
  38
  39 #ifndef nsEventQueue_h__
  40 #define nsEventQueue_h__
  41
  42 #include <stdlib.h>
  43 #include "prmon.h"
  44 #include "nsIRunnable.h"
  45
  46 // A threadsafe FIFO event queue...
  47 class NS_COM nsEventQueue
  48 {
  49 public:
  50   nsEventQueue();
  51   ~nsEventQueue();
  52
  53   // Returns "true" if the event queue has been completely constructed.
  54   PRBool IsInitialized() { return mMonitor != nsnull; }
  55
  56   // This method adds a new event to the pending event queue.  The event object
  57   // is AddRef'd if this method succeeds.  This method returns PR_TRUE if the
  58   // event was stored in the event queue, and it returns PR_FALSE if it could
  59   // not allocate sufficient memory.
  60   PRBool PutEvent(nsIRunnable *event);
  61
  62   // This method gets an event from the event queue.  If mayWait is true, then
  63   // the method will block the calling thread until an event is available.  If
  64   // the event is null, then the method returns immediately indicating whether
  65   // or not an event is pending.  When the resulting event is non-null, the
  66   // caller is responsible for releasing the event object.  This method does
  67   // not alter the reference count of the resulting event.
  68   PRBool GetEvent(PRBool mayWait, nsIRunnable **event);
  69
  70   // This method returns true if there is a pending event.
  71   PRBool HasPendingEvent() {
  72     return GetEvent(PR_FALSE, nsnull);
  73   }
  74
  75   // This method returns the next pending event or null.
  76   PRBool GetPendingEvent(nsIRunnable **runnable) {
  77     return GetEvent(PR_FALSE, runnable);
  78   }
  79
  80   // This method waits for and returns the next pending event.
  81   PRBool WaitPendingEvent(nsIRunnable **runnable) {
  82     return GetEvent(PR_TRUE, runnable);
  83   }
  84
  85   // Expose the event queue's monitor for "power users"
  86   PRMonitor *Monitor() {
  87     return mMonitor;
  88   }
  89
  90 private:
  91
  92   PRBool IsEmpty() {
  93     return !mHead || (mHead == mTail && mOffsetHead == mOffsetTail);
  94   }
  95
  96   enum { EVENTS_PER_PAGE = 250 };
  97
  98   // Page objects are linked together to form a simple deque.
  99
 100   struct Page; friend struct Page; // VC6!
 101   struct Page {
 102     struct Page *mNext;
 103     nsIRunnable *mEvents[EVENTS_PER_PAGE];
 104   };
 105
 106   static Page *NewPage() {
 107     return static_cast<Page *>(calloc(1, sizeof(Page)));
 108   }
 109
 110   static void FreePage(Page *p) {
 111     free(p);
 112   }
 113
 114   PRMonitor *mMonitor;
 115
 116   Page *mHead;
 117   Page *mTail;
 118
 119   PRUint16 mOffsetHead;  // offset into mHead where next item is removed
 120   PRUint16 mOffsetTail;  // offset into mTail where next item is added
 121 };
 122
 123 #endif  // nsEventQueue_h__