Special handling for macos dispatcher quirks

src/Avalonia.Base/Threading/Dispatcher.Queue.cs

@@ -9,7 +9,9 @@ public partial class Dispatcher
     private readonly DispatcherPriorityQueue _queue = new();
     private bool _signaled;
     private bool _explicitBackgroundProcessingRequested;
-    private const int MaximumTimeProcessingBackgroundJobs = 50;
+    private const int MaximumInputStarvationTimeInFallbackMode = 50;
+    private const int MaximumInputStarvationTimeInExplicitProcessingExplicitMode = 50;
+    private int _maximumInputStarvationTime;
 
     void RequestBackgroundProcessing()
     {
@@ -35,8 +37,8 @@ private void OnReadyForExplicitBackgroundProcessing()
         lock (InstanceLock)
         {
             _explicitBackgroundProcessingRequested = false;
-            ExecuteJobsCore();
         }
+        ExecuteJobsCore(true);
     }
 
     /// <summary>
@@ -130,10 +132,10 @@ private void Signaled()
         lock (InstanceLock)
             _signaled = false;
 
-        ExecuteJobsCore();
+        ExecuteJobsCore(false);
     }
 
-    void ExecuteJobsCore()
+    void ExecuteJobsCore(bool fromExplicitBackgroundProcessingCallback)
     {
         long? backgroundJobExecutionStartedAt = null;
         while (true)
@@ -151,7 +153,6 @@ void ExecuteJobsCore()
             if (job.Priority > DispatcherPriority.Input)
             {
                 ExecuteJob(job);
-                backgroundJobExecutionStartedAt = null;
             }
             // If platform supports pending input query, ask the platform if we can continue running low priority jobs
             else if (_pendingInputImpl?.CanQueryPendingInput == true)
@@ -164,14 +165,21 @@ void ExecuteJobsCore()
                     return;
                 }
             }
+            // We can't ask if the implementation has pending input, so we should let it to call us back
+            // Once it thinks that input is handled
+            else if (_backgroundProcessingImpl != null && !fromExplicitBackgroundProcessingCallback)
+            {
+                RequestBackgroundProcessing();
+                return;
+            }
             // We can't check if there is pending input, but still need to enforce interactivity
             // so we stop processing background jobs after some timeout and start a timer to continue later
             else
             {
                 if (backgroundJobExecutionStartedAt == null)
                     backgroundJobExecutionStartedAt = Now;
 
-                if (Now - backgroundJobExecutionStartedAt.Value > MaximumTimeProcessingBackgroundJobs)
+                if (Now - backgroundJobExecutionStartedAt.Value > _maximumInputStarvationTime)
                 {
                     _signaled = true;
                     RequestBackgroundProcessing();

src/Avalonia.Base/Threading/Dispatcher.Timers.cs

@@ -127,7 +127,7 @@ private void OnOSTimer()
         if (needToPromoteTimers)
             PromoteTimers();
         if (needToProcessQueue)
-            ExecuteJobsCore();
+            ExecuteJobsCore(false);
         UpdateOSTimer();
     }
 

src/Avalonia.Base/Threading/Dispatcher.cs

@@ -34,6 +34,9 @@ internal Dispatcher(IDispatcherImpl impl)
         _controlledImpl = _impl as IControlledDispatcherImpl;
         _pendingInputImpl = _impl as IDispatcherImplWithPendingInput;
         _backgroundProcessingImpl = _impl as IDispatcherImplWithExplicitBackgroundProcessing;
+        _maximumInputStarvationTime = _backgroundProcessingImpl == null ?
+            MaximumInputStarvationTimeInFallbackMode :
+            MaximumInputStarvationTimeInExplicitProcessingExplicitMode;
         if (_backgroundProcessingImpl != null)
             _backgroundProcessingImpl.ReadyForBackgroundProcessing += OnReadyForExplicitBackgroundProcessing;
     }

src/Avalonia.Base/Threading/DispatcherFrame.cs

@@ -38,10 +38,14 @@ public DispatcherFrame() : this(true)
     ///        for their important criteria to be met.  These frames
     ///        should have a timeout associated with them.
     /// </param>
-    public DispatcherFrame(bool exitWhenRequested)
+    public DispatcherFrame(bool exitWhenRequested) : this(Dispatcher.UIThread, exitWhenRequested)
     {
-        Dispatcher = Dispatcher.UIThread;
         Dispatcher.VerifyAccess();
+    }
+
+    internal DispatcherFrame(Dispatcher dispatcher, bool exitWhenRequested)
+    {
+        Dispatcher = dispatcher;
         _exitWhenRequested = exitWhenRequested;
         _continue = true;
     }