caching the CancellationToken will prevent race condition (#2125)

To be a good citizen, it is important that the caller of this method can (and should) call Dispose() on the returned token source. The problem though, is that each time cts.Token was called before, it would try to create a new CancellationToken which means that it could throw an ObjectDisposed exception leading to noisy logs.

src/Proto.Actor/Timers/Scheduler.cs

@@ -11,7 +11,7 @@ namespace Proto.Timers;
 /// </summary>
 /// <remarks>
 ///     The user is responsible for cancelling sends. They will not be automatically
-///     cancelled when this object is distroyed and will be left around in the background.
+///     cancelled when this object is destroyed and will be left around in the background.
 /// </remarks>
 [PublicAPI]
 public class Scheduler
@@ -37,13 +37,14 @@ public Scheduler(ISenderContext context)
     public CancellationTokenSource SendOnce(TimeSpan delay, PID target, object message)
     {
         var cts = new CancellationTokenSource();
+        var token = cts.Token;
 
         _ = SafeTask.Run(async () =>
             {
-                await Task.Delay(delay, cts.Token).ConfigureAwait(false);
+                await Task.Delay(delay, token).ConfigureAwait(false);
 
                 _context.Send(target, message);
-            }, cts.Token
+            }, token
         );
 
         return cts;
@@ -70,28 +71,19 @@ public CancellationTokenSource SendRepeatedly(TimeSpan interval, PID target, obj
     public CancellationTokenSource SendRepeatedly(TimeSpan delay, TimeSpan interval, PID target, object message)
     {
         var cts = new CancellationTokenSource();
+        var token = cts.Token;
 
         _ = SafeTask.Run(async () =>
             {
-                await Task.Delay(delay, cts.Token).ConfigureAwait(false);
+                await Task.Delay(delay, token).ConfigureAwait(false);
 
-                async Task Trigger()
+                while (!cts.IsCancellationRequested)
                 {
-                    while (true)
-                    {
-                        if (cts.IsCancellationRequested)
-                        {
-                            return;
-                        }
+                    _context.Send(target, message);
 
-                        _context.Send(target, message);
-
-                        await Task.Delay(interval, cts.Token).ConfigureAwait(false);
-                    }
+                    await Task.Delay(interval, token).ConfigureAwait(false);
                 }
-
-                await Trigger().ConfigureAwait(false);
-            }, cts.Token
+            }, token
         );
 
         return cts;
@@ -109,28 +101,19 @@ async Task Trigger()
     public CancellationTokenSource RequestRepeatedly(TimeSpan delay, TimeSpan interval, PID target, object message)
     {
         var cts = new CancellationTokenSource();
+        var token = cts.Token;
 
         _ = SafeTask.Run(async () =>
             {
-                await Task.Delay(delay, cts.Token).ConfigureAwait(false);
+                await Task.Delay(delay, token).ConfigureAwait(false);
 
-                async Task Trigger()
+                while (!cts.IsCancellationRequested)
                 {
-                    while (true)
-                    {
-                        if (cts.IsCancellationRequested)
-                        {
-                            return;
-                        }
+                    _context.Request(target, message);
 
-                        _context.Request(target, message);
-
-                        await Task.Delay(interval, cts.Token).ConfigureAwait(false);
-                    }
+                    await Task.Delay(interval, token).ConfigureAwait(false);
                 }
-
-                await Trigger().ConfigureAwait(false);
-            }, cts.Token
+            }, token
         );
 
         return cts;