dont allow new writes if theres a write with delayed completion

2 files changed, 3 insertions, 2 deletions

diff --git a/src/csharp/Grpc.Core/Internal/AsyncCall.cs b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
index db40b553ce..264c28ae7a 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCall.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
@@ -372,7 +372,8 @@ namespace Grpc.Core.Internal
         private Task CheckSendPreconditionsClientSide()
         {
             GrpcPreconditions.CheckState(!halfcloseRequested, "Request stream has already been completed.");
-            GrpcPreconditions.CheckState(streamingWriteTcs == null, "Only one write can be pending at a time.");
+            // if there is a delayed streaming write, we will treat that as if the write was still in progress until the call finishes.
+            GrpcPreconditions.CheckState(streamingWriteTcs == null && (finished || delayedStreamingWriteTcs == null), "Only one write can be pending at a time.");
 
             if (cancelRequested)
             {
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
index 50fdfa9006..8d9f548d62 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
@@ -208,7 +208,7 @@ namespace Grpc.Core.Internal
         {
             GrpcPreconditions.CheckState(!halfcloseRequested, "Response stream has already been completed.");
             GrpcPreconditions.CheckState(!finished, "Already finished.");
-            GrpcPreconditions.CheckState(streamingWriteTcs == null, "Only one write can be pending at a time");
+            GrpcPreconditions.CheckState(streamingWriteTcs == null && delayedStreamingWriteTcs == null, "Only one write can be pending at a time");
             GrpcPreconditions.CheckState(!disposed);
 
             return null;