Change scheduler list to be queue-like

The scheduler modifies the SchedulerData list mainly in two ways:
1. Remove a finished item
2. Append a new item

This optimizes the Append operation by keeping a last element
pointer, so we don't have to walk the whole list to find it. This
way this list is converted to a queue-like structure.

Change-Id: If7214e1f6016414551abbef11f26f332737f7893

2 files changed, 24 insertions, 18 deletions

diff --git a/vcl/inc/svdata.hxx b/vcl/inc/svdata.hxx
index e9a80f28a64d..f9de696650ad 100644
--- a/vcl/inc/svdata.hxx
+++ b/vcl/inc/svdata.hxx
@@ -66,10 +66,6 @@ class Image;
 class PopupMenu;
 class Application;
 class OutputDevice;
-namespace vcl
-{
-    class Window;
-}
 class SystemWindow;
 class WorkWindow;
 class Dialog;
@@ -101,7 +97,13 @@ class OpenGLContext;
 #define SV_ICON_ID_DATABASE                            12
 #define SV_ICON_ID_FORMULA                             13
 
-namespace vcl { class DisplayConnectionDispatch; class SettingsConfigItem; class DeleteOnDeinitBase; }
+namespace vcl
+{
+    class DisplayConnectionDispatch;
+    class SettingsConfigItem;
+    class DeleteOnDeinitBase;
+    class Window;
+}
 
 class LocaleConfigurationListener : public utl::ConfigurationListener
 {
@@ -320,6 +322,7 @@ struct BlendFrameCache
 struct ImplSchedulerContext
 {
     ImplSchedulerData*      mpFirstSchedulerData = nullptr; ///< list of all active tasks
+    ImplSchedulerData*      mpLastSchedulerData = nullptr;  ///< last item of the mpFirstSchedulerData list
     SalTimer*               mpSalTimer = nullptr;           ///< interface to sal event loop / system timer
     sal_uInt64              mnTimerPeriod = 0;              ///< current timer period
     sal_uInt64              mnLastProcessTime = 0;          ///< last time a task was processed
diff --git a/vcl/source/app/scheduler.cxx b/vcl/source/app/scheduler.cxx
index dc6ff9fab5a9..9b954f4a1c3f 100644
--- a/vcl/source/app/scheduler.cxx
+++ b/vcl/source/app/scheduler.cxx
@@ -107,7 +107,8 @@ void Scheduler::ImplDeInitScheduler()
     }
 
     rSchedCtx.mpFirstSchedulerData = nullptr;
-    rSchedCtx.mnTimerPeriod = 0;
+    rSchedCtx.mpLastSchedulerData  = nullptr;
+    rSchedCtx.mnTimerPeriod        = 0;
 }
 
 /**
@@ -234,6 +235,8 @@ bool Scheduler::ProcessTaskScheduling( bool bIdle )
                 pPrevSchedulerData->mpNext = pSchedulerData->mpNext;
             else
                 rSchedCtx.mpFirstSchedulerData = pSchedulerData->mpNext;
+            if ( !pSchedulerData->mpNext )
+                rSchedCtx.mpLastSchedulerData = pPrevSchedulerData;
             if ( pSchedulerData->mpTask )
                 pSchedulerData->mpTask->mpSchedulerData = nullptr;
             ImplSchedulerData *pDeleteItem = pSchedulerData;
@@ -333,23 +336,23 @@ void Task::Start()
     if ( !mpSchedulerData )
     {
         // insert Task
-        mpSchedulerData                = new ImplSchedulerData;
-        mpSchedulerData->mpTask        = this;
-        mpSchedulerData->mbInScheduler = false;
+        ImplSchedulerData* pSchedulerData = new ImplSchedulerData;
+        pSchedulerData->mpTask            = this;
+        pSchedulerData->mbInScheduler     = false;
+        pSchedulerData->mpNext            = nullptr;
+        mpSchedulerData = pSchedulerData;
 
         // insert last due to SFX!
-        ImplSchedulerData* pPrev = nullptr;
-        ImplSchedulerData* pData = rSchedCtx.mpFirstSchedulerData;
-        while ( pData )
+        if ( !rSchedCtx.mpLastSchedulerData )
         {
-            pPrev = pData;
-            pData = pData->mpNext;
+            rSchedCtx.mpFirstSchedulerData = pSchedulerData;
+            rSchedCtx.mpLastSchedulerData = pSchedulerData;
         }
-        mpSchedulerData->mpNext = nullptr;
-        if ( pPrev )
-            pPrev->mpNext = mpSchedulerData;
         else
-            rSchedCtx.mpFirstSchedulerData = mpSchedulerData;
+        {
+            rSchedCtx.mpLastSchedulerData->mpNext = pSchedulerData;
+            rSchedCtx.mpLastSchedulerData = pSchedulerData;
+        }
         SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks()
                   << " " << mpSchedulerData << "  added      " << *this );
     }