Fix race conditions in tests

test/Polly.Core.Tests/Hedging/HedgingResilienceStrategyTests.cs

@@ -15,7 +15,7 @@ public class HedgingResilienceStrategyTests : IDisposable
     private static readonly TimeSpan AssertTimeout = TimeSpan.FromSeconds(15);
 
     private readonly HedgingStrategyOptions<string> _options = new();
-    private readonly List<TelemetryEventArguments> _events = new();
+    private readonly ConcurrentQueue<TelemetryEventArguments> _events = new();
     private readonly ResilienceStrategyTelemetry _telemetry;
     private readonly HedgingTimeProvider _timeProvider;
     private readonly HedgingActions _actions;
@@ -27,7 +27,7 @@ public class HedgingResilienceStrategyTests : IDisposable
 
     public HedgingResilienceStrategyTests(ITestOutputHelper testOutput)
     {
-        _telemetry = TestUtilities.CreateResilienceTelemetry(_events.Add);
+        _telemetry = TestUtilities.CreateResilienceTelemetry(_events.Enqueue);
         _timeProvider = new HedgingTimeProvider { AutoAdvance = _options.HedgingDelay };
         _actions = new HedgingActions(_timeProvider);
         _primaryTasks = new PrimaryStringTasks(_timeProvider);

test/Polly.Core.Tests/Hedging/HedgingTimeProvider.cs

@@ -20,14 +20,14 @@ public void Advance(TimeSpan diff)
 
     public Func<int> TimeStampProvider { get; set; } = () => 0;
 
-    public List<TimerEntry> TimerEntries { get; } = new List<TimerEntry>();
+    public ConcurrentQueue<TimerEntry> TimerEntries { get; } = new();
 
     public override DateTimeOffset GetUtcNow() => _utcNow;
 
     public override ITimer CreateTimer(TimerCallback callback, object? state, TimeSpan dueTime, TimeSpan period)
     {
         var entry = new TimerEntry(dueTime, new TaskCompletionSource<bool>(), _utcNow.Add(dueTime), () => callback(state));
-        TimerEntries.Add(entry);
+        TimerEntries.Enqueue(entry);
 
         Advance(AutoAdvance);
 

test/Polly.TestUtils/TestUtilities.cs

@@ -105,6 +105,7 @@ public static ResilienceContext WithResultType<T>(this ResilienceContext context
     private sealed class CallbackDiagnosticSource : DiagnosticSource
     {
         private readonly Action<TelemetryEventArguments> _callback;
+        private readonly object _syncRoot = new();
 
         public CallbackDiagnosticSource(Action<TelemetryEventArguments> callback) => _callback = callback;
 
@@ -122,7 +123,11 @@ public override void Write(string name, object? value)
 
             // copy the args because these are pooled and in tests we want to preserve them
             args = TelemetryEventArguments.Get(args.Source, args.EventName, args.Context, args.Outcome, arguments);
-            _callback(args);
+
+            lock (_syncRoot)
+            {
+                _callback(args);
+            }
         }
     }
 }