The CustomSyncrhonizationContext is designed to run a single task.

As such, the Run method should never be called more than once.
Make the constructor and Run method private and add a public static Run method to
run a single task on an instance of the context.

Author: David Ellingsworth

src/RestSharp/AsyncHelpers.cs

@@ -25,9 +25,7 @@ static class AsyncHelpers {
     /// </summary>
     /// <param name="task">Callback for asynchronous task to run</param>
     static void RunSync(Func<Task> task) {
-        var customContext  = new CustomSynchronizationContext(task);
-
-        customContext.Run();
+        CustomSynchronizationContext.Run(task);
     }
 
     /// <summary>
@@ -56,7 +54,7 @@ class CustomSynchronizationContext : SynchronizationContext {
         /// Constructor for the custom context
         /// </summary>
         /// <param name="task">Task to execute</param>
-        public CustomSynchronizationContext(Func<Task> task) =>
+        private CustomSynchronizationContext(Func<Task> task) =>
             _task = task ?? throw new ArgumentNullException(nameof(task), "Please remember to pass a Task to be executed");
 
         /// <summary>
@@ -72,7 +70,7 @@ public override void Post(SendOrPostCallback function, object? state) {
         /// <summary>
         /// Enqueues the function to be executed and executes all resulting continuations until it is completely done
         /// </summary>
-        public void Run() {
+        private void Run() {
             var currentContext = SynchronizationContext.Current;
 
             try {
@@ -117,6 +115,12 @@ async void PostCallback(object? _) {
             }
         }
 
+        public static void Run(Func<Task> task) {
+            var customContext = new CustomSynchronizationContext(task);
+
+            customContext.Run();
+        }
+
         /// <summary>
         /// When overridden in a derived class, dispatches a synchronous message to a synchronization context.
         /// </summary>