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      1 /*
      2  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14  *     its contributors may be used to endorse or promote products derived
     15  *     from this software without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #include "config.h"
     30 #include "WorkQueue.h"
     31 
     32 #include "WorkQueueItem.h"
     33 #include <wtf/Assertions.h>
     34 
     35 static const unsigned queueLength = 1024;
     36 
     37 static WorkQueueItem* theQueue[queueLength];
     38 static unsigned startOfQueue;
     39 static unsigned endOfQueue;
     40 
     41 WorkQueue* WorkQueue::shared()
     42 {
     43     static WorkQueue* sharedInstance = new WorkQueue;
     44     return sharedInstance;
     45 }
     46 
     47 WorkQueue::WorkQueue()
     48     : m_frozen(false)
     49 {
     50 }
     51 
     52 void WorkQueue::queue(WorkQueueItem* item)
     53 {
     54     ASSERT(endOfQueue < queueLength);
     55     ASSERT(endOfQueue >= startOfQueue);
     56 
     57     if (m_frozen) {
     58         delete item;
     59         return;
     60     }
     61 
     62     theQueue[endOfQueue++] = item;
     63 }
     64 
     65 WorkQueueItem* WorkQueue::dequeue()
     66 {
     67     ASSERT(endOfQueue >= startOfQueue);
     68 
     69     if (startOfQueue == endOfQueue)
     70         return 0;
     71 
     72     return theQueue[startOfQueue++];
     73 }
     74 
     75 unsigned WorkQueue::count()
     76 {
     77     return endOfQueue - startOfQueue;
     78 }
     79 
     80 void WorkQueue::clear()
     81 {
     82     for (unsigned i = startOfQueue; i < endOfQueue; ++i) {
     83         delete theQueue[i];
     84         theQueue[i] = 0;
     85     }
     86 
     87     startOfQueue = 0;
     88     endOfQueue = 0;
     89 }
     90 
     91 bool WorkQueue::processWork()
     92 {
     93     bool startedLoad = false;
     94 
     95     while (!startedLoad && count()) {
     96         WorkQueueItem* item = dequeue();
     97         ASSERT(item);
     98         startedLoad = item->invoke();
     99         delete item;
    100     }
    101 
    102     // If we're done and we didn't start a load, then we're really done, so return true.
    103     return !startedLoad;
    104 }
    105