From b1f600dd21cf2efa60958d18becaf2e90d67b01a Mon Sep 17 00:00:00 2001
From: Alexey Fedorov <mail@alexeyfv.ru>
Date: Thu, 27 Mar 2025 20:32:15 +0100
Subject: [PATCH 1/2] Fix multiple calls of the same async subscribers when
 dispatching events

---
 .../DispatchToEventSubscribersTests.cs        | 26 +++++++++++++++++++
 .../Subscribers/DispatchToEventSubscribers.cs |  2 ++
 2 files changed, 28 insertions(+)

diff --git a/Source/EventFlow.Tests/UnitTests/Subscribers/DispatchToEventSubscribersTests.cs b/Source/EventFlow.Tests/UnitTests/Subscribers/DispatchToEventSubscribersTests.cs
index 14af8edfb..2b76e6dd6 100644
--- a/Source/EventFlow.Tests/UnitTests/Subscribers/DispatchToEventSubscribersTests.cs
+++ b/Source/EventFlow.Tests/UnitTests/Subscribers/DispatchToEventSubscribersTests.cs
@@ -122,6 +122,20 @@ public void SubscriberExceptionIsThrownIfConfigured()
             _logMock.VerifyNoProblems();
         }
 
+        [Test]
+        public async Task OnlyOneAsynchronousSubscriberGetCalled()
+        {
+            // Arrange
+            var subscriberMock = ArrangeMultipleAsynchronousSubscribers<ThingyPingEvent>();
+
+            // Act
+            await Sut.DispatchToAsynchronousSubscribersAsync(A<DomainEvent<ThingyAggregate, ThingyId, ThingyPingEvent>>(), CancellationToken.None).ConfigureAwait(false);
+
+            // Assert
+            subscriberMock.Verify(s => s.HandleAsync(It.IsAny<IDomainEvent<ThingyAggregate, ThingyId, ThingyPingEvent>>(), It.IsAny<CancellationToken>()), Times.Once);
+            _logMock.VerifyNoProblems();
+        }
+
         private Mock<ISubscribeSynchronousTo<ThingyAggregate, ThingyId, TEvent>> ArrangeSynchronousSubscriber<TEvent>()
             where TEvent : IAggregateEvent<ThingyAggregate, ThingyId>
         {
@@ -146,5 +160,17 @@ private Mock<ISubscribeAsynchronousTo<ThingyAggregate, ThingyId, TEvent>> Arrang
 
             return subscriberMock;
         }
+
+        private Mock<ISubscribeAsynchronousTo<ThingyAggregate, ThingyId, TEvent>> ArrangeMultipleAsynchronousSubscribers<TEvent>()
+            where TEvent : IAggregateEvent<ThingyAggregate, ThingyId>
+        {
+            var subscriberMock = new Mock<ISubscribeAsynchronousTo<ThingyAggregate, ThingyId, TEvent>>();
+
+            _serviceProviderMock
+                .Setup(r => r.GetService(typeof(IEnumerable<ISubscribeAsynchronousTo<ThingyAggregate, ThingyId, TEvent>>)))
+                .Returns(new object[] { subscriberMock.Object, subscriberMock.Object, subscriberMock.Object });
+
+            return subscriberMock;
+        }
     }
 }
diff --git a/Source/EventFlow/Subscribers/DispatchToEventSubscribers.cs b/Source/EventFlow/Subscribers/DispatchToEventSubscribers.cs
index c7ff1f07b..7d72e5d35 100644
--- a/Source/EventFlow/Subscribers/DispatchToEventSubscribers.cs
+++ b/Source/EventFlow/Subscribers/DispatchToEventSubscribers.cs
@@ -127,6 +127,8 @@ private async Task DispatchToSubscribersAsync(
                 .ConfigureAwait(false);
             var subscribers = _serviceProvider.GetServices(subscriberInformation.SubscriberType)
                 .Cast<ISubscribe>()
+                .GroupBy(s => s.GetType())
+                .Select(g => g.First())
                 .OrderBy(s => s.GetType().Name)
                 .ToList();
 

From 3d56226da0a9bc2c7b00648336077fa1ea163dbf Mon Sep 17 00:00:00 2001
From: Alexey Fedorov <mail@alexeyfv.ru>
Date: Sun, 27 Apr 2025 10:32:14 +0200
Subject: [PATCH 2/2] Upate release notes

---
 RELEASE_NOTES.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 4b9b5204c..62ee9f622 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,6 +1,6 @@
 ### New in 1.2.1 (working version, not released yet)
 
-* *Nothing yet...*
+* Fix: Prevent multiple calls of the same async subscribers when dispatching events (by @alexeyfv)
 
 ### New in 1.2.0 (released 2025-03-09)