tdf#100337 Message boxes showup empty with white background

the bug here was that we had, on the stack, going into the scheduler
THREE times. Two of those were idles.

The original code would end up always picking the first idle from inside
    ImplSchedulerData::GetMostImportantTask
and then
    ImplSchedulerData::Invoke
would just return because we were still inside that Idle, and the second
Idle would never get executed

Since the second Idle was responsible for painting the dialog in the
bug, sometimes the dialog would never get painted.

Change-Id: Ia15b98a06e231c8e1c29450e05a76ad427e41e36
Reviewed-on: https://gerrit.libreoffice.org/31785
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
(cherry picked from commit 19a4eaab9a55a2ecb33b727bad6307c5a2badc23)
Reviewed-on: https://gerrit.libreoffice.org/31798
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

2 files changed, 37 insertions, 1 deletions

diff --git a/vcl/qa/cppunit/timer.cxx b/vcl/qa/cppunit/timer.cxx
index 07fdc92ffbac..ca7a0284e91a 100644
--- a/vcl/qa/cppunit/timer.cxx
+++ b/vcl/qa/cppunit/timer.cxx
@@ -66,6 +66,7 @@ public:
 #endif
     void testRecursiveTimer();
     void testSlowTimerCallback();
+    void testTriggerIdleFromIdle();
 
     CPPUNIT_TEST_SUITE(TimerTest);
     CPPUNIT_TEST(testIdle);
@@ -80,6 +81,7 @@ public:
 #endif
     CPPUNIT_TEST(testRecursiveTimer);
     CPPUNIT_TEST(testSlowTimerCallback);
+    CPPUNIT_TEST(testTriggerIdleFromIdle);
 
     CPPUNIT_TEST_SUITE_END();
 };
@@ -353,6 +355,39 @@ void TimerTest::testSlowTimerCallback()
         Application::Yield();
 }
 
+
+class TriggerIdleFromIdle : public Idle
+{
+    bool* mpTriggered;
+    TriggerIdleFromIdle* mpOther;
+public:
+    explicit TriggerIdleFromIdle( bool* pTriggered, TriggerIdleFromIdle* pOther ) :
+        Idle(), mpTriggered(pTriggered), mpOther(pOther)
+    {
+    }
+    virtual void Invoke() override
+    {
+        Start();
+        if (mpOther)
+            mpOther->Start();
+        Application::Yield();
+        if (mpTriggered)
+            *mpTriggered = true;
+    }
+};
+
+void TimerTest::testTriggerIdleFromIdle()
+{
+    bool bTriggered1 = false;
+    bool bTriggered2 = false;
+    TriggerIdleFromIdle aTest2( &bTriggered2, nullptr );
+    TriggerIdleFromIdle aTest1( &bTriggered1, &aTest2 );
+    aTest1.Start();
+    Application::Yield();
+    CPPUNIT_ASSERT_MESSAGE("idle triggered", bTriggered1);
+    CPPUNIT_ASSERT_MESSAGE("idle triggered", bTriggered2);
+}
+
 CPPUNIT_TEST_SUITE_REGISTRATION(TimerTest);
 
 CPPUNIT_PLUGIN_IMPLEMENT();
diff --git a/vcl/source/app/scheduler.cxx b/vcl/source/app/scheduler.cxx
index 4caa4d27e82e..c8f4054919d3 100644
--- a/vcl/source/app/scheduler.cxx
+++ b/vcl/source/app/scheduler.cxx
@@ -33,6 +33,7 @@ void ImplSchedulerData::Invoke()
 {
     DBG_TESTSOLARMUTEX();
 
+    assert(!mbInScheduler);
     if (mbDelete || mbInScheduler )
         return;
 
@@ -56,7 +57,7 @@ ImplSchedulerData *ImplSchedulerData::GetMostImportantTask( bool bTimerOnly )
     sal_uInt64 nTimeNow = tools::Time::GetSystemTicks();
     for ( ImplSchedulerData *pSchedulerData = pSVData->mpFirstSchedulerData; pSchedulerData; pSchedulerData = pSchedulerData->mpNext )
     {
-        if ( !pSchedulerData->mpScheduler || pSchedulerData->mbDelete ||
+        if ( !pSchedulerData->mpScheduler || pSchedulerData->mbDelete || pSchedulerData->mbInScheduler ||
              !pSchedulerData->mpScheduler->ReadyForSchedule( bTimerOnly, nTimeNow ) ||
              !pSchedulerData->mpScheduler->IsActive())
             continue;