Unlock scheduler in deinit for ProcessEventsToIdle

The scheduler is normally never locked when not processing its own
task lists. So while the fix is correct, that ProcessEventsToIdle
shouldn't run with a locked scheduler, just unlock it in the
actual shutdown case, where the deadlock occurred.

This also reverts commit 46f6b39c6d8acd064bafb2416feba757ba0d0fbc.

Change-Id: If1603c1563772dd1d156dc6d9bcddbf58aa721c1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/107241
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

4 files changed, 14 insertions, 20 deletions

diff --git a/vcl/README.scheduler b/vcl/README.scheduler
index 52c76dac5b85..718509033e79 100644
--- a/vcl/README.scheduler
+++ b/vcl/README.scheduler
@@ -58,6 +58,17 @@ Task::mpSchedulerData, which is actually a part of the scheduler.
 Before invoking the task, we have to release the lock, so others can
 Start new Tasks.
 
+The Scheduler just processes it's own Tasks in the main thread and needs
+the SolarMutex for it and for DeInit (tested by DBG_TESTSOLARMUTEX). All
+the other interaction just take the SchedulerMutex or don't need locking
+at all.
+
+There is a "workaround" for static Task objecs, which would crash LO on
+destruction, because Task::~Task would try to de-register itself in the
+Scheduler, while the SchedulerLock would be long gone. OTOH this makes
+Task handling less error-prone, than doing "special" manual cleanup.
+There is also a "= TODOs and ideas =" to get rid if static Tasks.
+
 
 = Lifecycle / thread-safety of Scheduler-based objects =
 
diff --git a/vcl/inc/schedulerimpl.hxx b/vcl/inc/schedulerimpl.hxx
index d95fb0157880..ffb08084252c 100644
--- a/vcl/inc/schedulerimpl.hxx
+++ b/vcl/inc/schedulerimpl.hxx
@@ -65,25 +65,6 @@ public:
     }
 };
 
-class SchedulerGuardReleaser final
-{
-public:
-    SchedulerGuardReleaser()
-    {
-        Scheduler::Lock();
-        m_nLockCount = Scheduler::Unlock(true) - 1;
-    }
-
-    ~SchedulerGuardReleaser()
-    {
-        if (m_nLockCount)
-            Scheduler::Lock(m_nLockCount);
-    }
-
-private:
-    sal_uInt32 m_nLockCount;
-};
-
 #endif // INCLUDED_VCL_INC_SCHEDULERIMPL_HXX
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/vcl/source/app/scheduler.cxx b/vcl/source/app/scheduler.cxx
index f9fc3dc01fc6..9ae60f3f344d 100644
--- a/vcl/source/app/scheduler.cxx
+++ b/vcl/source/app/scheduler.cxx
@@ -124,7 +124,10 @@ void Scheduler::ImplDeInitScheduler()
               "DeInit the scheduler - pending tasks: " << nTasks );
 
     // clean up all the sfx::SfxItemDisruptor_Impl Idles
+    sal_uInt32 nLockCount = Unlock(true);
+    assert(1 == nLockCount);
     ProcessEventsToIdle();
+    Lock(nLockCount);
 #endif
     rSchedCtx.mbActive = false;
 
diff --git a/vcl/source/app/svapp.cxx b/vcl/source/app/svapp.cxx
index 0b30a0b6b688..f91375e77edd 100644
--- a/vcl/source/app/svapp.cxx
+++ b/vcl/source/app/svapp.cxx
@@ -462,7 +462,6 @@ bool Application::Reschedule( bool i_bAllEvents )
 
 void Scheduler::ProcessEventsToIdle()
 {
-    SchedulerGuardReleaser aReleaser;
     int nSanity = 1;
     while( Application::Reschedule( true ) )
     {