Guard against work being queued on an already-disposed ThreadedTaskScheduler

osu.Framework.Tests/Threading/ThreadedTaskSchedulerTest.cs

@@ -65,5 +65,25 @@ public void EnsureEventualDisposalWithStuckTasks()
 
             Assert.That(exited.Wait(30000));
         }
+
+        [Test]
+        public void EnsureScheduledTaskReturnsOnDisposal()
+        {
+            ManualResetEventSlim exited = new ManualResetEventSlim();
+            ManualResetEventSlim run = new ManualResetEventSlim();
+            ThreadedTaskScheduler taskScheduler = new ThreadedTaskScheduler(4, "test");
+
+            taskScheduler.Dispose();
+
+            Task.Run(async () =>
+            {
+                // ReSharper disable once AccessToDisposedClosure
+                await Task.Factory.StartNew(() => { run.Set(); }, default, TaskCreationOptions.HideScheduler, taskScheduler).ConfigureAwait(false);
+                exited.Set();
+            });
+
+            Assert.That(run.Wait(30000));
+            Assert.That(exited.Wait(30000));
+        }
     }
 }

osu.Framework/Threading/ThreadedTaskScheduler.cs

@@ -10,6 +10,7 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using osu.Framework.Logging;
 
 namespace osu.Framework.Threading
 {
@@ -82,7 +83,19 @@ private void processTasks()
         /// Queues a Task to be executed by this scheduler.
         /// </summary>
         /// <param name="task">The task to be executed.</param>
-        protected override void QueueTask(Task task) => tasks.Add(task);
+        protected override void QueueTask(Task task)
+        {
+            try
+            {
+                tasks.Add(task);
+            }
+            catch (ObjectDisposedException)
+            {
+                // tasks may have been disposed. there's no easy way to check on this other than catch for it.
+                Logger.Log($"Task was queued for execution on a {nameof(ThreadedTaskScheduler)} ({name}) after it was disposed. The task will be executed inline.");
+                TryExecuteTask(task);
+            }
+        }
 
         /// <summary>
         /// Provides a list of the scheduled tasks for the debugger to consume.