Add the unref work items to the front of the workqueue (Bug #3273)

Ensures that memory still gets freed even if the workqueue is overloaded.

apps/openmw/mwworld/cellpreloader.cpp

@@ -238,7 +238,7 @@ namespace MWWorld
         }
 
         // the resource cache is cleared from the worker thread so that we're not holding up the main thread with delete operations
-        mWorkQueue->addWorkItem(new UpdateCacheItem(mResourceSystem, mTerrain, timestamp));
+        mWorkQueue->addWorkItem(new UpdateCacheItem(mResourceSystem, mTerrain, timestamp), true);
     }
 
     void CellPreloader::setExpiryDelay(double expiryDelay)

components/sceneutil/unrefqueue.cpp

@@ -40,7 +40,7 @@ namespace SceneUtil
         if (mWorkItem->mObjects.empty())
             return;
 
-        workQueue->addWorkItem(mWorkItem);
+        workQueue->addWorkItem(mWorkItem, true);
 
         mWorkItem = new UnrefWorkItem;
     }

components/sceneutil/workqueue.cpp

@@ -55,7 +55,7 @@ WorkQueue::~WorkQueue()
     {
         OpenThreads::ScopedLock<OpenThreads::Mutex> lock(mMutex);
         while (!mQueue.empty())
-            mQueue.pop();
+            mQueue.pop_back();
         mIsReleased = true;
         mCondition.broadcast();
     }
@@ -67,7 +67,7 @@ WorkQueue::~WorkQueue()
     }
 }
 
-void WorkQueue::addWorkItem(osg::ref_ptr<WorkItem> item)
+void WorkQueue::addWorkItem(osg::ref_ptr<WorkItem> item, bool front)
 {
     if (item->isDone())
     {
@@ -76,7 +76,10 @@ void WorkQueue::addWorkItem(osg::ref_ptr<WorkItem> item)
     }
 
     OpenThreads::ScopedLock<OpenThreads::Mutex> lock(mMutex);
-    mQueue.push(item);
+    if (front)
+        mQueue.push_front(item);
+    else
+        mQueue.push_back(item);
     mCondition.signal();
 }
 
@@ -90,7 +93,7 @@ osg::ref_ptr<WorkItem> WorkQueue::removeWorkItem()
     if (!mQueue.empty())
     {
         osg::ref_ptr<WorkItem> item = mQueue.front();
-        mQueue.pop();
+        mQueue.pop_front();
         return item;
     }
     else

components/sceneutil/workqueue.hpp

@@ -50,7 +50,8 @@ namespace SceneUtil
 
         /// Add a new work item to the back of the queue.
         /// @par The work item's waitTillDone() method may be used by the caller to wait until the work is complete.
-        void addWorkItem(osg::ref_ptr<WorkItem> item);
+        /// @param front If true, add item to the front of the queue. If false (default), add to the back.
+        void addWorkItem(osg::ref_ptr<WorkItem> item, bool front=false);
 
         /// Get the next work item from the front of the queue. If the queue is empty, waits until a new item is added.
         /// If the workqueue is in the process of being destroyed, may return NULL.
@@ -59,7 +60,7 @@ namespace SceneUtil
 
     private:
         bool mIsReleased;
-        std::queue<osg::ref_ptr<WorkItem> > mQueue;
+        std::deque<osg::ref_ptr<WorkItem> > mQueue;
 
         OpenThreads::Mutex mMutex;
         OpenThreads::Condition mCondition;