From 5e58062d5f5b8af0ce2e6b0be0e6a5ddc3613509 Mon Sep 17 00:00:00 2001
From: Danylo Fitel <danylo.fitel@outlook.com>
Date: Mon, 20 Apr 2020 17:12:36 -0700
Subject: [PATCH 1/2] Not resetting exception list to null in ReadExceptions,
 so that in case multiple tasks are finishing at the same time they will both
 read a non-empty list of exceptions.

Returning a copy of exception list from ReadExceptions to prevent concurrent reads by CompleteLoopNow and writes by tasks still running in case the loop was canceled.
---
 src/Extensions/ParallelForEachExtensions.cs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/Extensions/ParallelForEachExtensions.cs b/src/Extensions/ParallelForEachExtensions.cs
index 4c7d7f8..68ce8fd 100644
--- a/src/Extensions/ParallelForEachExtensions.cs
+++ b/src/Extensions/ParallelForEachExtensions.cs
@@ -76,11 +76,12 @@ public List<Exception> ReadExceptions()
                     _exceptionListLock.Enter(ref lockTaken);
                 try
                 {
-                    return _exceptionList;
+                    // Return a copy, so the list being returned will not be modified
+                    // by tasks that are still running if the loop was canceled
+                    return new List<Exception>(_exceptionList);
                 }
                 finally
                 {
-                    _exceptionList = null;
                     _exceptionListLock.Exit(useMemoryBarrier: false);
                 }
             }

From 4becfd4dd3fa0cb24027482d8f0207bf9f3cf9b6 Mon Sep 17 00:00:00 2001
From: Danylo Fitel <danylo.fitel@outlook.com>
Date: Mon, 17 Aug 2020 17:54:01 -0700
Subject: [PATCH 2/2] Fixing the happy path

---
 src/Extensions/ParallelForEachExtensions.cs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Extensions/ParallelForEachExtensions.cs b/src/Extensions/ParallelForEachExtensions.cs
index 68ce8fd..fa20ccf 100644
--- a/src/Extensions/ParallelForEachExtensions.cs
+++ b/src/Extensions/ParallelForEachExtensions.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -78,7 +79,7 @@ public List<Exception> ReadExceptions()
                 {
                     // Return a copy, so the list being returned will not be modified
                     // by tasks that are still running if the loop was canceled
-                    return new List<Exception>(_exceptionList);
+                    return new List<Exception>(_exceptionList ?? Enumerable.Empty<Exception>());
                 }
                 finally
                 {