From 9d5a4a9f5a9e545495b406b324515199a0f22a08 Mon Sep 17 00:00:00 2001
From: yomunsam <yomunsam@outlook.com>
Date: Sat, 7 Mar 2020 20:10:59 +0800
Subject: [PATCH] It seems that the problem has not been completely resolved
 just now

---
 Assets/UniRx.Async/UnityAsyncExtensions.cs | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/Assets/UniRx.Async/UnityAsyncExtensions.cs b/Assets/UniRx.Async/UnityAsyncExtensions.cs
index fdb6cd3..68aca43 100644
--- a/Assets/UniRx.Async/UnityAsyncExtensions.cs
+++ b/Assets/UniRx.Async/UnityAsyncExtensions.cs
@@ -792,14 +792,18 @@ namespace UniRx.Async
 
             public void UnsafeOnCompleted(Action continuation)
             {
-                if(asyncOperation != null && asyncOperation.isDone)
-                {
-                    continuation?.Invoke();
-                    return;
-                }
+                
                 Error.ThrowWhenContinuationIsAlreadyRegistered(continuationAction);
                 continuationAction = continuation.AsFuncOfT<AsyncOperation>();
-                asyncOperation.completed += continuationAction;
+                lock (asyncOperation)
+                {
+                    if (asyncOperation.isDone)
+                    {
+                        continuation?.Invoke();
+                        return;
+                    }
+                    asyncOperation.completed += continuationAction;
+                }
             }
         }