tdf#100092: Deterministic scheduling to prevent unpredictable behavior.

Low priority idles can fire more or less randomly, and consequently two
consequent runs of LibreOffice differ in the amount of the idles that have
been performed during an operation.

This commit adds a possibility to turn on a 'deterministic mode' where two
subsequent runs of LibreOffice trigger about the same amount of events when
they perform the same set of operations.

Change-Id: I92566ef4eee20e7d604cfd48f01c4df30c77e653
Reviewed-on: https://gerrit.libreoffice.org/25712
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

5 files changed, 67 insertions, 9 deletions

diff --git a/include/vcl/scheduler.hxx b/include/vcl/scheduler.hxx
index 95303ee48f5e..ee83c1e89e9e 100644
--- a/include/vcl/scheduler.hxx
+++ b/include/vcl/scheduler.hxx
@@ -53,6 +53,7 @@ protected:
     // These should be constexpr static, when supported.
     static const sal_uInt64 ImmediateTimeoutMs = 1;
     static const sal_uInt64 MaximumTimeoutMs = 1000 * 60; // 1 minute
+    static const sal_uInt64 InfiniteTimeoutMs = 1000 * 60 * 60 * 24; // 1 day
 
     static void ImplStartTimer(sal_uInt64 nMS, bool bForce = false);
 
@@ -90,7 +91,7 @@ public:
     Scheduler&      operator=( const Scheduler& rScheduler );
     static void ImplDeInitScheduler();
 
-    // Process one pending Timer with highhest priority
+    /// Process one pending Timer with highhest priority
     static void CallbackTaskScheduling( bool ignore );
     /// Calculate minimum timeout - and return its value.
     static sal_uInt64 CalculateMinimumTimeout( bool &bHasActiveIdles );
@@ -98,6 +99,12 @@ public:
     static bool       ProcessTaskScheduling( bool bTimerOnly );
     /// Process all events until we are idle
     static void       ProcessEventsToIdle();
+
+    /// Control the deterministic mode.  In this mode, two subsequent runs of
+    /// LibreOffice fire about the same amount idles.
+    static void SetDeterministicMode(bool bDeterministic);
+    /// Return the current state of deterministic mode.
+    static bool GetDeterministicMode();
 };
 
 #endif // INCLUDED_VCL_SCHEDULER_HXX
diff --git a/offapi/com/sun/star/awt/XToolkitExperimental.idl b/offapi/com/sun/star/awt/XToolkitExperimental.idl
index 7c5d36331958..89828b2864e1 100644
--- a/offapi/com/sun/star/awt/XToolkitExperimental.idl
+++ b/offapi/com/sun/star/awt/XToolkitExperimental.idl
@@ -19,14 +19,18 @@ module com {  module sun {  module star {  module awt {
 
 interface XToolkitExperimental : XToolkit2
 {
-  /** Process all pending idle events
-   */
-  void processEventsToIdle();
+    /** Process all pending idle events
+     */
+    void processEventsToIdle();
 
 
-  /** Get the number of OpenGL buffer swaps.
-   */
-  hyper getOpenGLBufferSwapCounter();
+    /** Get the number of OpenGL buffer swaps.
+     */
+    hyper getOpenGLBufferSwapCounter();
+
+    /** Turn on or off deterministic scheduling (off is the default).
+     */
+    void setDeterministicScheduling([in] boolean bDeterministicMode);
 };
 
 }; }; }; };
diff --git a/toolkit/source/awt/vclxtoolkit.cxx b/toolkit/source/awt/vclxtoolkit.cxx
index 3b5548be561b..262697baa903 100644
--- a/toolkit/source/awt/vclxtoolkit.cxx
+++ b/toolkit/source/awt/vclxtoolkit.cxx
@@ -199,6 +199,9 @@ public:
     virtual sal_Int64 SAL_CALL getOpenGLBufferSwapCounter()
         throw (css::uno::RuntimeException, std::exception) override;
 
+    virtual void SAL_CALL setDeterministicScheduling(sal_Bool bDeterministicMode)
+        throw (css::uno::RuntimeException, std::exception) override;
+
     // css::awt::XToolkit
     css::uno::Reference< css::awt::XWindowPeer >  SAL_CALL getDesktopWindow(  ) throw(css::uno::RuntimeException, std::exception) override;
     css::awt::Rectangle                                        SAL_CALL getWorkArea(  ) throw(css::uno::RuntimeException, std::exception) override;
@@ -1922,7 +1925,14 @@ void SAL_CALL VCLXToolkit::processEventsToIdle()
 sal_Int64 SAL_CALL VCLXToolkit::getOpenGLBufferSwapCounter()
     throw (css::uno::RuntimeException, std::exception)
 {
-     return OpenGLWrapper::getBufferSwapCounter();
+    return OpenGLWrapper::getBufferSwapCounter();
+}
+
+void SAL_CALL VCLXToolkit::setDeterministicScheduling(sal_Bool bDeterministicMode)
+    throw (css::uno::RuntimeException, std::exception)
+{
+    SolarMutexGuard aSolarGuard;
+    Scheduler::SetDeterministicMode(bDeterministicMode);
 }
 
 // css:awt:XToolkitRobot
diff --git a/vcl/source/app/idle.cxx b/vcl/source/app/idle.cxx
index 123f37a13e4f..587e05fc2d98 100644
--- a/vcl/source/app/idle.cxx
+++ b/vcl/source/app/idle.cxx
@@ -44,7 +44,23 @@ Idle::Idle( const Idle& rIdle ) : Scheduler(rIdle)
 void Idle::Start()
 {
     Scheduler::Start();
-    Scheduler::ImplStartTimer(Scheduler::ImmediateTimeoutMs);
+
+    sal_uInt64 nPeriod = Scheduler::ImmediateTimeoutMs;
+    if (Scheduler::GetDeterministicMode())
+    {
+        switch (mePriority)
+        {
+            case SchedulerPriority::LOW:
+            case SchedulerPriority::LOWER:
+            case SchedulerPriority::LOWEST:
+                nPeriod = Scheduler::InfiniteTimeoutMs;
+                break;
+            default:
+                break;
+        }
+    }
+
+    Scheduler::ImplStartTimer(nPeriod);
 }
 
 bool Idle::ReadyForSchedule( bool bTimerOnly, sal_uInt64 /* nTimeNow */ ) const
@@ -67,6 +83,15 @@ sal_uInt64 Idle::UpdateMinPeriod( sal_uInt64 nMinPeriod, sal_uInt64 /* nTime */
     case SchedulerPriority::REPAINT:
         nMinPeriod = ImmediateTimeoutMs; // don't wait.
         break;
+    case SchedulerPriority::LOW:
+    case SchedulerPriority::LOWER:
+    case SchedulerPriority::LOWEST:
+        if (Scheduler::GetDeterministicMode())
+        {
+            nMinPeriod = Scheduler::InfiniteTimeoutMs;
+            break;
+        }
+        // fall-through intended
     default:
         // FIXME: tdf#92036 workaround, I should be 1 too - wait 5ms
         if (nMinPeriod > 5) // only shrink the min. period if nothing is quicker.
diff --git a/vcl/source/app/scheduler.cxx b/vcl/source/app/scheduler.cxx
index 879ca422a5ac..efb65ca110d2 100644
--- a/vcl/source/app/scheduler.cxx
+++ b/vcl/source/app/scheduler.cxx
@@ -174,6 +174,18 @@ bool Scheduler::ProcessTaskScheduling( bool bTimerOnly )
         return false;
 }
 
+static bool g_bDeterministicMode = false;
+
+void Scheduler::SetDeterministicMode(bool bDeterministic)
+{
+    g_bDeterministicMode = bDeterministic;
+}
+
+bool Scheduler::GetDeterministicMode()
+{
+    return g_bDeterministicMode;
+}
+
 sal_uInt64 Scheduler::CalculateMinimumTimeout( bool &bHasActiveIdles )
 {
     // process all pending Tasks