Add some Scheduler unit tests and logging

1. calling Start() for invoked tasks
2. correctly schedule by priority
3. self-stopping AutoTimer

This also adds SAL_INFO output to Scheduler and Task to log the
scheduling processing tasks.

Change-Id: I3c8a708d1fd51c550320f8af3f9486c43c32e358

16 files changed, 265 insertions, 51 deletions

diff --git a/include/vcl/svapp.hxx b/include/vcl/svapp.hxx
index 0891859c79e1..c108d4b6d992 100644
--- a/include/vcl/svapp.hxx
+++ b/include/vcl/svapp.hxx
@@ -462,18 +462,25 @@ public:
     */
     static void                 Quit();
 
-    /** Attempt to reschedule in processing of current event(s)
+    /** Attempt to process current pending event(s)
+
+     It doesn't sleep if no events are available for processing.
 
      @param bAllEvents  If set to true, then try to process all the
         events. If set to false, then only process the current
         event. Defaults to false.
 
+     @returns true if any event was processed.
+
      @see Execute, Quit, Yield, EndYield, GetSolarMutex,
           GetMainThreadIdentifier, ReleaseSolarMutex, AcquireSolarMutex,
      */
-    static void                 Reschedule( bool bAllEvents = false );
+    static bool                 Reschedule( bool bAllEvents = false );
+
+    /** Process the next event.
 
-    /** Allow processing of the next event.
+     It sleeps if no event is available for processing and just returns
+     if an event was processed.
 
      @see Execute, Quit, Reschedule, EndYield, GetSolarMutex,
           GetMainThreadIdentifier, ReleaseSolarMutex, AcquireSolarMutex,
diff --git a/vcl/inc/headless/svpinst.hxx b/vcl/inc/headless/svpinst.hxx
index 731642f5762c..4a82c413372a 100644
--- a/vcl/inc/headless/svpinst.hxx
+++ b/vcl/inc/headless/svpinst.hxx
@@ -157,6 +157,7 @@ public:
     // and timer
     virtual SalYieldResult  DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong nReleased) override;
     virtual bool            AnyInput( VclInputFlags nType ) override;
+    virtual bool            IsMainThread() const override { return true; }
 
     // may return NULL to disable session management
     virtual SalSession*     CreateSalSession() override;
diff --git a/vcl/inc/osx/salinst.h b/vcl/inc/osx/salinst.h
index 6570ab32a7e2..b92a2aa35665 100644
--- a/vcl/inc/osx/salinst.h
+++ b/vcl/inc/osx/salinst.h
@@ -142,7 +142,8 @@ public:
     void PostUserEvent( AquaSalFrame* pFrame, SalEvent nType, void* pData );
     void delayedSettingsChanged( bool bInvalidate );
 
-    bool isNSAppThread() const;
+    // Is this the NSAppThread?
+    virtual bool IsMainThread() const override;
 
     void startedPrintJob() { mnActivePrintJobs++; }
     void endedPrintJob() { mnActivePrintJobs--; }
diff --git a/vcl/inc/salinst.hxx b/vcl/inc/salinst.hxx
index ca8017d94513..0e2703af8999 100644
--- a/vcl/inc/salinst.hxx
+++ b/vcl/inc/salinst.hxx
@@ -127,6 +127,7 @@ public:
     virtual void            AcquireYieldMutex( sal_uLong nCount ) = 0;
     // return true, if yield mutex is owned by this thread, else false
     virtual bool            CheckYieldMutex() = 0;
+    virtual bool            IsMainThread() const = 0;
 
     /**
      * Wait for the next event (if bWait) and dispatch it,
diff --git a/vcl/inc/saltimer.hxx b/vcl/inc/saltimer.hxx
index 234a18228af2..fcf450d28a7b 100644
--- a/vcl/inc/saltimer.hxx
+++ b/vcl/inc/saltimer.hxx
@@ -21,10 +21,9 @@
 #define INCLUDED_VCL_INC_SALTIMER_HXX
 
 #include <sal/config.h>
-
 #include <vcl/dllapi.h>
-
 #include <salwtype.hxx>
+#include <iostream>
 
 /*
  * note: there will be only a single instance of SalTimer
@@ -72,6 +71,15 @@ struct ImplSchedulerData
     const char *GetDebugName() const;
 };
 
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const ImplSchedulerData& data )
+{
+    stream << " i: " << data.mbInScheduler
+           << " d: " << data.mbDelete;
+    return stream;
+}
+
 #endif // INCLUDED_VCL_INC_SALTIMER_HXX
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/vcl/inc/unx/gtk/gtkinst.hxx b/vcl/inc/unx/gtk/gtkinst.hxx
index 250fd9b1ca1b..983fbf287deb 100644
--- a/vcl/inc/unx/gtk/gtkinst.hxx
+++ b/vcl/inc/unx/gtk/gtkinst.hxx
@@ -210,6 +210,8 @@ public:
 
     virtual SalYieldResult      DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong nReleased) override;
     virtual bool                AnyInput( VclInputFlags nType ) override;
+    // impossible to handle correctly, as "main thread" depends on the dispatch mutex
+    virtual bool                IsMainThread() const override { return false; }
 
     virtual GenPspGraphics     *CreatePrintGraphics() override;
 
diff --git a/vcl/inc/unx/salinst.h b/vcl/inc/unx/salinst.h
index f3ca193df205..1f9c43bf2232 100644
--- a/vcl/inc/unx/salinst.h
+++ b/vcl/inc/unx/salinst.h
@@ -76,6 +76,7 @@ public:
 
     virtual SalYieldResult      DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong nReleased) override;
     virtual bool                AnyInput( VclInputFlags nType ) override;
+    virtual bool                IsMainThread() const override { return true; }
 
     virtual OUString            GetConnectionIdentifier() override;
     void                        SetLib( SalXLib *pXLib ) { mpXLib = pXLib; }
diff --git a/vcl/inc/win/salinst.h b/vcl/inc/win/salinst.h
index 25b4afb17aa0..022f67e0557a 100644
--- a/vcl/inc/win/salinst.h
+++ b/vcl/inc/win/salinst.h
@@ -62,6 +62,7 @@ public:
     virtual sal_uIntPtr         ReleaseYieldMutex() override;
     virtual void                AcquireYieldMutex( sal_uIntPtr nCount ) override;
     virtual bool                CheckYieldMutex() override;
+    virtual bool                IsMainThread() const override;
 
     virtual SalYieldResult      DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong nReleased) override;
     virtual bool                AnyInput( VclInputFlags nType ) override;
diff --git a/vcl/osx/salinst.cxx b/vcl/osx/salinst.cxx
index 0a1dd479af0d..c73f94685f07 100644
--- a/vcl/osx/salinst.cxx
+++ b/vcl/osx/salinst.cxx
@@ -445,7 +445,7 @@ bool AquaSalInstance::CheckYieldMutex()
     return bRet;
 }
 
-bool AquaSalInstance::isNSAppThread() const
+bool AquaSalInstance::IsMainThread() const
 {
     return osl::Thread::getCurrentIdentifier() == maMainThread;
 }
@@ -607,7 +607,7 @@ SalYieldResult AquaSalInstance::DoYield(bool bWait, bool bHandleAllCurrentEvents
     // handle cocoa event queue
     // cocoa events may be only handled in the thread the NSApp was created
     bool bHadEvent = false;
-    if( isNSAppThread() && mnActivePrintJobs == 0 )
+    if( IsMainThread() && mnActivePrintJobs == 0 )
     {
         // we need to be woken up by a cocoa-event
         // if a user event should be posted by the event handling below
@@ -742,7 +742,7 @@ bool AquaSalInstance::AnyInput( VclInputFlags nType )
         }
     }
 
-    if (![NSThread isMainThread])
+    if (!IsMainThread())
         return false;
 
     unsigned/*NSUInteger*/ nEventMask = 0;
@@ -1019,7 +1019,7 @@ OUString AquaSalInstance::getOSVersion()
 YieldMutexReleaser::YieldMutexReleaser() : mnCount( 0 )
 {
     SalData* pSalData = GetSalData();
-    if( ! pSalData->mpFirstInstance->isNSAppThread() )
+    if( ! pSalData->mpFirstInstance->IsMainThread() )
     {
         SalData::ensureThreadAutoreleasePool();
         mnCount = pSalData->mpFirstInstance->ReleaseYieldMutex();
diff --git a/vcl/osx/saltimer.cxx b/vcl/osx/saltimer.cxx
index b28a6598cec6..9b2c1df83c83 100644
--- a/vcl/osx/saltimer.cxx
+++ b/vcl/osx/saltimer.cxx
@@ -33,7 +33,7 @@ bool AquaSalTimer::bDispatchTimer = false;
 void ImplSalStartTimer( sal_uLong nMS )
 {
     SalData* pSalData = GetSalData();
-    if( pSalData->mpFirstInstance->isNSAppThread() )
+    if( !pSalData->mpFirstInstance->IsMainThread() )
     {
         AquaSalTimer::bDispatchTimer = true;
         NSTimeInterval aTI = double(nMS)/1000.0;
diff --git a/vcl/qa/cppunit/timer.cxx b/vcl/qa/cppunit/timer.cxx
index 47439ad19e8b..83b0a7cc01e5 100644
--- a/vcl/qa/cppunit/timer.cxx
+++ b/vcl/qa/cppunit/timer.cxx
@@ -64,9 +64,12 @@ public:
     void testAutoTimer();
     void testMultiAutoTimers();
 #endif
-    void testRecursiveTimer();
+    void testAutoTimerStop();
+    void testNestedTimer();
     void testSlowTimerCallback();
     void testTriggerIdleFromIdle();
+    void testInvokedReStart();
+    void testPriority();
 
     CPPUNIT_TEST_SUITE(TimerTest);
     CPPUNIT_TEST(testIdle);
@@ -79,9 +82,12 @@ public:
     CPPUNIT_TEST(testAutoTimer);
     CPPUNIT_TEST(testMultiAutoTimers);
 #endif
-    CPPUNIT_TEST(testRecursiveTimer);
+    CPPUNIT_TEST(testAutoTimerStop);
+    CPPUNIT_TEST(testNestedTimer);
     CPPUNIT_TEST(testSlowTimerCallback);
     CPPUNIT_TEST(testTriggerIdleFromIdle);
+    CPPUNIT_TEST(testInvokedReStart);
+    CPPUNIT_TEST(testPriority);
 
     CPPUNIT_TEST_SUITE_END();
 };
@@ -100,7 +106,7 @@ class IdleBool : public Idle
     bool &mrBool;
 public:
     explicit IdleBool( bool &rBool ) :
-        Idle(), mrBool( rBool )
+        Idle( "IdleBool" ), mrBool( rBool )
     {
         SetPriority( TaskPriority::LOWEST );
         Start();
@@ -117,7 +123,7 @@ void TimerTest::testIdle()
 {
     bool bTriggered = false;
     IdleBool aTest( bTriggered );
-    Scheduler::ProcessTaskScheduling( true );
+    while ( Application::Reschedule() );
     CPPUNIT_ASSERT_MESSAGE("idle triggered", bTriggered);
 }
 
@@ -148,7 +154,7 @@ class TimerBool : public Timer
     bool &mrBool;
 public:
     TimerBool( sal_uLong nMS, bool &rBool ) :
-        Timer(), mrBool( rBool )
+        Timer( "TimerBool" ), mrBool( rBool )
     {
         SetTimeout( nMS );
         Start();
@@ -180,17 +186,26 @@ void TimerTest::testDurations()
 class AutoTimerCount : public AutoTimer
 {
     sal_Int32 &mrCount;
+    const sal_Int32 mnMaxCount;
+
 public:
-    AutoTimerCount( sal_uLong nMS, sal_Int32 &rCount ) :
-        AutoTimer(), mrCount( rCount )
+    AutoTimerCount( sal_uLong nMS, sal_Int32 &rCount,
+                    const sal_Int32 nMaxCount = -1 )
+        : AutoTimer( "AutoTimerCount" )
+        , mrCount( rCount )
+        , mnMaxCount( nMaxCount )
     {
         SetTimeout( nMS );
         Start();
         mrCount = 0;
     }
+
     virtual void Invoke() override
     {
-        mrCount++;
+        ++mrCount;
+        CPPUNIT_ASSERT( mnMaxCount < 0 || mrCount <= mnMaxCount );
+        if ( mrCount == mnMaxCount )
+            Stop();
     }
 };
 
@@ -296,11 +311,22 @@ void TimerTest::testMultiAutoTimers()
 }
 #endif // TEST_TIMERPRECISION
 
+void TimerTest::testAutoTimerStop()
+{
+    sal_Int32 nTimerCount = 0;
+    const sal_Int32 nMaxCount = 5;
+    AutoTimerCount aAutoTimer( 0, nTimerCount, nMaxCount );
+    while ( nMaxCount != nTimerCount )
+        Application::Yield();
+    CPPUNIT_ASSERT( !aAutoTimer.IsActive() );
+    CPPUNIT_ASSERT( !Application::Reschedule() );
+}
+
 
 class YieldTimer : public Timer
 {
 public:
-    explicit YieldTimer( sal_uLong nMS ) : Timer()
+    explicit YieldTimer( sal_uLong nMS ) : Timer( "YieldTimer" )
     {
         SetTimeout( nMS );
         Start();
@@ -312,7 +338,7 @@ public:
     }
 };
 
-void TimerTest::testRecursiveTimer()
+void TimerTest::testNestedTimer()
 {
     sal_Int32 nCount = 0;
     YieldTimer aCount(5);
@@ -328,7 +354,7 @@ class SlowCallbackTimer : public Timer
     bool &mbSlow;
 public:
     SlowCallbackTimer( sal_uLong nMS, bool &bBeenSlow ) :
-        Timer(), mbSlow( bBeenSlow )
+        Timer( "SlowCallbackTimer" ), mbSlow( bBeenSlow )
     {
         SetTimeout( nMS );
         Start();
@@ -362,7 +388,7 @@ class TriggerIdleFromIdle : public Idle
     TriggerIdleFromIdle* mpOther;
 public:
     explicit TriggerIdleFromIdle( bool* pTriggered, TriggerIdleFromIdle* pOther ) :
-        Idle(), mpTriggered(pTriggered), mpOther(pOther)
+        Idle( "TriggerIdleFromIdle" ), mpTriggered(pTriggered), mpOther(pOther)
     {
     }
     virtual void Invoke() override
@@ -388,6 +414,79 @@ void TimerTest::testTriggerIdleFromIdle()
     CPPUNIT_ASSERT_MESSAGE("idle triggered", bTriggered2);
 }
 
+
+class IdleInvokedReStart : public Idle
+{
+    sal_Int32 &mrCount;
+public:
+    IdleInvokedReStart( sal_Int32 &rCount )
+        : Idle( "IdleInvokedReStart" ), mrCount( rCount )
+    {
+        Start();
+    }
+    virtual void Invoke() override
+    {
+        mrCount++;
+        if ( mrCount < 2 )
+            Start();
+    }
+};
+
+void TimerTest::testInvokedReStart()
+{
+    sal_Int32 nCount = 0;
+    IdleInvokedReStart aIdle( nCount );
+    while ( Application::Reschedule() );
+    CPPUNIT_ASSERT_EQUAL( nCount, sal_Int32(2) );
+}
+
+
+class IdleSerializer : public Idle
+{
+    sal_uInt32 mnPosition;
+    sal_uInt32 &mrProcesed;
+public:
+    IdleSerializer( const sal_Char *pDebugName,
+                    sal_uInt32 nPosition, sal_uInt32 &rProcesed )
+        : Idle( pDebugName )
+        , mnPosition( nPosition )
+        , mrProcesed( rProcesed )
+    {
+        Start();
+    }
+    virtual void Invoke() override
+    {
+        ++mrProcesed;
+        CPPUNIT_ASSERT_EQUAL_MESSAGE( "Ignored prio", mnPosition, mrProcesed );
+    }
+};
+
+void TimerTest::testPriority()
+{
+    // scope, so tasks are deleted
+    {
+        // Start: 1st Idle low, 2nd high
+        sal_uInt32 nProcessed = 0;
+        IdleSerializer aLowPrioIdle( "IdleSerializer LowPrio", 2, nProcessed );
+        aLowPrioIdle.SetPriority( TaskPriority::LOWEST );
+        IdleSerializer aHighPrioIdle( "IdleSerializer HighPrio", 1, nProcessed );
+        aHighPrioIdle.SetPriority( TaskPriority::HIGHEST );
+        while ( Application::Reschedule() );
+        CPPUNIT_ASSERT_EQUAL_MESSAGE( "Not all idles processed", sal_uInt32(2), nProcessed );
+    }
+
+    {
+        // Start: 1st Idle high, 2nd low
+        sal_uInt32 nProcessed = 0;
+        IdleSerializer aHighPrioIdle( "IdleSerializer HighPrio", 1, nProcessed );
+        aHighPrioIdle.SetPriority( TaskPriority::HIGHEST );
+        IdleSerializer aLowPrioIdle( "IdleSerializer LowPrio", 2, nProcessed );
+        aLowPrioIdle.SetPriority( TaskPriority::LOWEST );
+        while ( Application::Reschedule() );
+        CPPUNIT_ASSERT_EQUAL_MESSAGE( "Not all idles processed", sal_uInt32(2), nProcessed );
+    }
+}
+
 CPPUNIT_TEST_SUITE_REGISTRATION(TimerTest);
 
 CPPUNIT_PLUGIN_IMPLEMENT();
diff --git a/vcl/source/app/scheduler.cxx b/vcl/source/app/scheduler.cxx
index 1c52ad170d28..2b372a6616e0 100644
--- a/vcl/source/app/scheduler.cxx
+++ b/vcl/source/app/scheduler.cxx
@@ -19,13 +19,58 @@
 
 #include <svdata.hxx>
 #include <tools/time.hxx>
-#include <vcl/scheduler.hxx>
+#include <vcl/idle.hxx>
 #include <saltimer.hxx>
 #include <salinst.hxx>
 #include <comphelper/profilezone.hxx>
 
 namespace {
 const sal_uInt64 MaximumTimeoutMs = 1000 * 60; // 1 minute
+
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const Task& task )
+{
+    stream << "a: " << task.IsActive() << " p: " << (int) task.GetPriority();
+    const sal_Char *name = task.GetDebugName();
+    if( nullptr == name )
+        return stream << " (nullptr)";
+    else
+        return stream << " " << name;
+}
+
+/**
+ * clang won't compile this in the Timer.hxx header, even with a class Idle
+ * forward definition, due to the incomplete Idle type in the template.
+ * Currently the code is just used in the Scheduler, so we keep it local.
+ *
+ * @see http://clang.llvm.org/compatibility.html#undep_incomplete
+ */
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const Timer& timer )
+{
+    bool bIsIdle = (dynamic_cast<const Idle*>( &timer ) != nullptr);
+    stream << (bIsIdle ? "Idle " : "Timer")
+           << " a: " << timer.IsActive() << " p: " << (int) timer.GetPriority();
+    const sal_Char *name = timer.GetDebugName();
+    if ( nullptr == name )
+        stream << " (nullptr)";
+    else
+        stream << " " << name;
+    if ( !bIsIdle )
+        stream << " " << timer.GetTimeout() << "ms";
+    stream << " (" << &timer << ")";
+    return stream;
+}
+
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const Idle& idle )
+{
+    return stream << static_cast<const Timer*>( &idle );
+}
+
 }
 
 void ImplSchedulerData::Invoke()
@@ -140,6 +185,7 @@ bool Scheduler::ProcessTaskScheduling( bool bIdle )
              !pSchedulerData->mpTask->ReadyForSchedule( bIdle, nTime ) ||
              !pSchedulerData->mpTask->IsActive())
             continue;
+
         if (!pMostUrgent)
             pMostUrgent = pSchedulerData;
         else
@@ -156,7 +202,8 @@ bool Scheduler::ProcessTaskScheduling( bool bIdle )
     {
         ::comphelper::ProfileZone aZone( pMostUrgent->GetDebugName() );
 
-        SAL_INFO("vcl.schedule", "Invoke task " << pMostUrgent->GetDebugName());
+        SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks() << " "
+                  << pMostUrgent << "  invoke     " << *pMostUrgent->mpTask );
 
         pMostUrgent->mnUpdateTime = nTime;
         pMostUrgent->Invoke();
@@ -192,6 +239,18 @@ sal_uInt64 Scheduler::CalculateMinimumTimeout( bool &bHasActiveIdles )
     pSchedulerData = pSVData->mpFirstSchedulerData;
     while ( pSchedulerData )
     {
+        const Timer *timer = dynamic_cast<Timer*>( pSchedulerData->mpTask );
+        if ( timer )
+            SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks() << " "
+                << pSchedulerData << " " << *pSchedulerData << " " << *timer );
+        else if ( pSchedulerData->mpTask )
+            SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks() << " "
+                << pSchedulerData << " " << *pSchedulerData
+                << " " << *pSchedulerData->mpTask );
+        else
+            SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks() << " "
+                << pSchedulerData << " " << *pSchedulerData << " (to be deleted)" );
+
         ImplSchedulerData *pNext = pSchedulerData->mpNext;
 
         // Should Task be released from scheduling?
@@ -216,10 +275,6 @@ sal_uInt64 Scheduler::CalculateMinimumTimeout( bool &bHasActiveIdles )
                     sal_uInt64 nOldMinPeriod = nMinPeriod;
                     nMinPeriod = pSchedulerData->mpTask->UpdateMinPeriod(
                                                            nOldMinPeriod, nTime );
-                    SAL_INFO("vcl.schedule", "Have active timer '" <<
-                             pSchedulerData->GetDebugName() <<
-                             "' update min period from " << nOldMinPeriod <<
-                             " to " << nMinPeriod);
                     assert( nMinPeriod <= nOldMinPeriod );
                     if ( nMinPeriod > nOldMinPeriod )
                     {
@@ -229,11 +284,7 @@ sal_uInt64 Scheduler::CalculateMinimumTimeout( bool &bHasActiveIdles )
                     }
                 }
                 else
-                {
-                    SAL_INFO("vcl.schedule", "Have active idle '" <<
-                             pSchedulerData->GetDebugName() << "'");
                     bHasActiveIdles = true;
-                }
             }
             pPrevSchedulerData = pSchedulerData;
         }
@@ -309,15 +360,22 @@ void Task::Start()
             pPrev->mpNext = mpSchedulerData;
         else
             pSVData->mpFirstSchedulerData = mpSchedulerData;
+        SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks()
+                  << " " << mpSchedulerData << "  added      " << *this );
     }
+    else
+        SAL_INFO( "vcl.schedule", tools::Time::GetSystemTicks()
+                  << " " << mpSchedulerData << "  restarted  " << *this );
+
     mpSchedulerData->mbDelete      = false;
     mpSchedulerData->mnUpdateTime  = tools::Time::GetSystemTicks();
 }
 
 void Task::Stop()
 {
+    SAL_INFO_IF( mbActive, "vcl.schedule", tools::Time::GetSystemTicks()
+                  << " " << mpSchedulerData << "  stopped    " << *this );
     mbActive = false;
-
     if ( mpSchedulerData )
         mpSchedulerData->mbDelete = true;
 }
diff --git a/vcl/source/app/svapp.cxx b/vcl/source/app/svapp.cxx
index c4d22d397013..fff8619d51fc 100644
--- a/vcl/source/app/svapp.cxx
+++ b/vcl/source/app/svapp.cxx
@@ -516,9 +516,9 @@ inline bool ImplYield(bool i_bWait, bool i_bAllEvents, sal_uLong const nReleased
     return bHasActiveIdles || eResult == SalYieldResult::EVENT;
 }
 
-void Application::Reschedule( bool i_bAllEvents )
+bool Application::Reschedule( bool i_bAllEvents )
 {
-    ImplYield(false, i_bAllEvents, 0);
+    return ImplYield(false, i_bAllEvents, 0);
 }
 
 void Scheduler::ProcessEventsToSignal(bool& bSignal)
@@ -541,6 +541,30 @@ void Scheduler::ProcessEventsToIdle()
             break;
         }
     }
+#if OSL_DEBUG_LEVEL > 0
+    // If we yield from a non-main thread we just can guarantee that all idle
+    // events were processed at some point, but our check can't prevent further
+    // processing in the main thread, which may add new events, so skip it.
+    const ImplSVData* pSVData = ImplGetSVData();
+    if ( !pSVData->mpDefInst->IsMainThread() )
+        return;
+    const ImplSchedulerData* pSchedulerData = ImplGetSVData()->mpFirstSchedulerData;
+    bool bAnyIdle = false;
+    while ( pSchedulerData )
+    {
+        if ( pSchedulerData->mpTask && !pSchedulerData->mbInScheduler )
+        {
+            Idle *pIdle = dynamic_cast<Idle*>( pSchedulerData->mpTask );
+            if ( pIdle && pIdle->IsActive() )
+            {
+                bAnyIdle = true;
+                SAL_WARN( "vcl.schedule",  "Unprocessed Idle: " << pIdle->GetDebugName() );
+            }
+        }
+        pSchedulerData = pSchedulerData->mpNext;
+    }
+    assert( !bAnyIdle );
+#endif
 }
 
 extern "C" {
diff --git a/vcl/unx/kde4/KDESalInstance.cxx b/vcl/unx/kde4/KDESalInstance.cxx
index dfe02cd36e2e..56f3df9465cb 100644
--- a/vcl/unx/kde4/KDESalInstance.cxx
+++ b/vcl/unx/kde4/KDESalInstance.cxx
@@ -25,6 +25,8 @@
 #include "KDEXLib.hxx"
 #include "KDESalDisplay.hxx"
 
+#include <QtGui/QApplication>
+#include <QtCore/QThread>
 #include <QX11Info>
 
 using namespace com::sun::star;
@@ -58,4 +60,9 @@ SalX11Display* KDESalInstance::CreateDisplay() const
     return new SalKDEDisplay( QX11Info::display() );
 }
 
+bool KDESalInstance::IsMainThread() const
+{
+    return qApp->thread() == QThread::currentThread();
+}
+
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/vcl/unx/kde4/KDESalInstance.hxx b/vcl/unx/kde4/KDESalInstance.hxx
index 54a0b405d96f..7b7417caaaf1 100644
--- a/vcl/unx/kde4/KDESalInstance.hxx
+++ b/vcl/unx/kde4/KDESalInstance.hxx
@@ -26,18 +26,20 @@ class SalFrame;
 
 class KDESalInstance : public X11SalInstance
 {
-    protected:
-        virtual SalX11Display* CreateDisplay() const override;
+protected:
+    virtual SalX11Display* CreateDisplay() const override;
 
-    public:
-        explicit KDESalInstance(SalYieldMutex* pMutex);
-        virtual SalFrame* CreateFrame( SalFrame* pParent, SalFrameStyleFlags nStyle ) override;
+public:
+    explicit KDESalInstance(SalYieldMutex* pMutex);
+    virtual SalFrame* CreateFrame( SalFrame* pParent, SalFrameStyleFlags nStyle ) override;
 
-        virtual bool hasNativeFileSelection() const override { return true; }
+    virtual bool hasNativeFileSelection() const override { return true; }
 
-        virtual css::uno::Reference< css::ui::dialogs::XFilePicker2 >
-            createFilePicker( const css::uno::Reference<
-                                  css::uno::XComponentContext >& ) override;
+    virtual css::uno::Reference< css::ui::dialogs::XFilePicker2 >
+        createFilePicker( const css::uno::Reference<
+                              css::uno::XComponentContext >& ) override;
+
+    virtual bool IsMainThread() const override;
 };
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/vcl/win/app/salinst.cxx b/vcl/win/app/salinst.cxx
index 78147ae67608..1fbdda70b261 100644
--- a/vcl/win/app/salinst.cxx
+++ b/vcl/win/app/salinst.cxx
@@ -188,10 +188,7 @@ void ImplSalYieldMutexAcquireWithWait()
     if ( !pInst )
         return;
 
-    DWORD nThreadId = GetCurrentThreadId();
-    SalData* pSalData = GetSalData();
-
-    if ( pSalData->mnAppThreadId == nThreadId )
+    if ( pInst->IsMainThread() )
     {
         // tdf#96887 If this is the main thread, then we must wait for two things:
         // - the mpSalYieldMutex being freed
@@ -594,13 +591,18 @@ ImplSalYield( bool bWait, bool bHandleAllCurrentEvents )
                      SalYieldResult::TIMEOUT;
 }
 
+bool WinSalInstance::IsMainThread() const
+{
+    const SalData* pSalData = GetSalData();
+    return pSalData->mnAppThreadId == GetCurrentThreadId();
+}
+
 SalYieldResult WinSalInstance::DoYield(bool bWait, bool bHandleAllCurrentEvents, sal_uLong const nReleased)
 {
     SalYieldResult eDidWork = SalYieldResult::TIMEOUT;
     // NOTE: if nReleased != 0 this will be called without SolarMutex
     //       so don't do anything dangerous before releasing it here
     SalYieldMutex*  pYieldMutex = mpSalYieldMutex;
-    SalData*        pSalData = GetSalData();
     DWORD           nCurThreadId = GetCurrentThreadId();
     sal_uLong const nCount = (nReleased != 0)
                                 ? nReleased
@@ -611,7 +613,7 @@ SalYieldResult WinSalInstance::DoYield(bool bWait, bool bHandleAllCurrentEvents,
         pYieldMutex->release();
         n--;
     }
-    if ( pSalData->mnAppThreadId != nCurThreadId )
+    if ( !IsMainThread() )
     {
         // #97739# A SendMessage call blocks until the called thread (here: the main thread)
         // returns. During a yield however, messages are processed in the main thread that might