Change Queue to ConcurrentQueue

RichardSzalay.MockHttp.Tests/MockHttpMessageHandlerTests.cs

@@ -1,6 +1,9 @@
 using System;
+using System.Collections.Concurrent;
+using System.Linq;
 using System.Net;
 using System.Net.Http;
+using System.Threading;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -232,6 +235,29 @@ public void Should_not_match_expect_out_of_order()
         Assert.Equal(HttpStatusCode.NotFound, result.StatusCode);
     }
 
+    [Fact]
+    public async Task Should_work_with_multiple_concurrent_writes_to_queue()
+    {
+        var mockHandler = new MockHttpMessageHandler();
+        var tasks = new ConcurrentQueue<Task>();
+        var readyEvent = new ManualResetEvent(false);
+
+        for (int i = 0; i < 100; i++)
+        {
+            tasks.Enqueue(Task.Run(async () =>
+            {
+                await Task.Yield();
+                readyEvent.WaitOne();
+                mockHandler
+                    .Expect("/test")
+                    .Respond("application/json", "{'status' : 'First'}");
+            }));
+        }
+        readyEvent.Set();
+
+        await Task.WhenAll(tasks).ConfigureAwait(false);
+    }
+
     [Fact]
     public void VerifyNoOutstandingExpectation_should_fail_if_outstanding_expectation()
     {

RichardSzalay.MockHttp/MockHttpMessageHandler.cs

@@ -1,5 +1,6 @@
 using RichardSzalay.MockHttp.Matchers;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http;
@@ -13,7 +14,7 @@ namespace RichardSzalay.MockHttp;
 /// </summary>
 public class MockHttpMessageHandler : HttpMessageHandler
 {
-    private Queue<IMockedRequest> requestExpectations = new();
+    private ConcurrentQueue<IMockedRequest> requestExpectations = new();
     private List<IMockedRequest> backendDefinitions = new();
     private Dictionary<IMockedRequest, int> matchCounts = new();
     private object lockObject = new();
@@ -108,15 +109,25 @@ private IMockedRequest FindHandler(HttpRequestMessage request)
 
         if (requestExpectations.Count > 0)
         {
-            var handler = requestExpectations.Peek();
-            var handlerResult = EvaluateMockedRequest(handler, request);
+            var peeked = requestExpectations.TryPeek(out var peekedHandler);
+            if (!peeked)
+            {
+                throw new InvalidOperationException("Concurrent read/write on mock queue");
+            }
+
+            var handlerResult = EvaluateMockedRequest(peekedHandler!, request);
             results.RequestExpectationResult = handlerResult;
 
             results.UnevaluatedRequestExpectations.AddRange(requestExpectations.Skip(1));
 
             if (handlerResult.Success)
             {
-                requestExpectations.Dequeue();
+                requestExpectations.TryDequeue(out var handler);
+
+                if (peekedHandler != handler)
+                {
+                    throw new Exception("Queue order changed between evaluation and result");
+                }
 
                 results.Handler = handler;
             }
@@ -366,7 +377,14 @@ public void VerifyNoOutstandingExpectation()
     /// </summary>
     public void ResetExpectations()
     {
+#if NET5_0_OR_GREATER
         requestExpectations.Clear();
+#else
+        while (!requestExpectations.IsEmpty)
+        {
+            requestExpectations.TryDequeue(out IMockedRequest _);
+        }
+#endif
     }
 
     /// <summary>