Respect IsFlowSuppressed when capturing execution context for suspension.

Author: VSadov

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

@@ -31,6 +31,9 @@ internal struct ExecutionAndSyncBlockStore
         public void Push()
         {
             _thread = Thread.CurrentThread;
+            // Here we get the execution context for synchronous restoring,
+            // not for flowing across suspension to potentially another thread.
+            // Therefore we do not need to worry about IsFlowSuppressed
             _previousExecutionCtx = _thread._executionContext;
             _previousSyncCtx = _thread._synchronizationContext;
         }
@@ -178,6 +181,9 @@ private struct RuntimeAsyncAwaitState
             public void CaptureContexts()
             {
                 Thread curThread = Thread.CurrentThreadAssumedInitialized;
+                // Here we get the execution context for presenting to the notifier,
+                // not for flowing across suspension to potentially another thread.
+                // Therefore we do not need to worry about IsFlowSuppressed
                 ExecutionContext = curThread._executionContext;
                 SynchronizationContext = curThread._synchronizationContext;
             }
@@ -775,10 +781,19 @@ private static ValueTask ValueTaskFromException(Exception ex)
             return new ValueTask<T?>(TaskFromException<T>(ex));
         }
 
+        // Called when capturing execution context for suspension.
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static ExecutionContext? CaptureExecutionContext()
         {
-            return Thread.CurrentThreadAssumedInitialized._executionContext;
+            ExecutionContext? executionContext = Thread.CurrentThreadAssumedInitialized._executionContext;
+            if (executionContext?.m_isFlowSuppressed == true)
+            {
+                // 'null' is the internal representation of default execution
+                // context that contains no variables.
+                executionContext = null;
+            }
+
+            return executionContext;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -796,6 +811,9 @@ private static void RestoreExecutionContext(ExecutionContext? previousExecCtx)
         private static void CaptureContexts(out ExecutionContext? execCtx, out SynchronizationContext? syncCtx)
         {
             Thread thread = Thread.CurrentThreadAssumedInitialized;
+            // Here we get the execution context for synchronous restoring,
+            // not for flowing across suspension to potentially another thread.
+            // Therefore we do not need to worry about IsFlowSuppressed
             execCtx = thread._executionContext;
             syncCtx = thread._synchronizationContext;
         }

src/libraries/System.Private.CoreLib/src/System/Threading/ExecutionContext.cs

@@ -24,7 +24,7 @@ public sealed class ExecutionContext : IDisposable, ISerializable
 
         private readonly IAsyncLocalValueMap? m_localValues;
         private readonly IAsyncLocal[]? m_localChangeNotifications;
-        private readonly bool m_isFlowSuppressed;
+        internal readonly bool m_isFlowSuppressed;
         private readonly bool m_isDefault;
 
         private ExecutionContext()