JIT: Move Thread sync and exec context save/restore to happen around runtime async bodies

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

@@ -534,7 +534,7 @@ public static void HandleSuspended<T, TOps>(T task) where T : Task, ITaskComplet
                 sentinelContinuation.Next = null;
 
                 // Head continuation should be the result of async call to AwaitAwaiter or UnsafeAwaitAwaiter.
-                // These never have special continuation handling.
+                // These never have special continuation context handling.
                 const ContinuationFlags continueFlags =
                     ContinuationFlags.ContinueOnCapturedSynchronizationContext |
                     ContinuationFlags.ContinueOnThreadPool |
@@ -753,35 +753,39 @@ private static void CaptureContexts(out ExecutionContext? execCtx, out Synchroni
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static void RestoreContexts(bool suspended, ExecutionContext? previousExecCtx, SynchronizationContext? previousSyncCtx)
+        private static void RestoreContexts(bool started, ExecutionContext? previousExecCtx, SynchronizationContext? previousSyncCtx)
         {
-            Thread thread = Thread.CurrentThreadAssumedInitialized;
-            if (!suspended && previousSyncCtx != thread._synchronizationContext)
+            if (started)
             {
-                thread._synchronizationContext = previousSyncCtx;
-            }
+                Thread thread = Thread.CurrentThreadAssumedInitialized;
+                if (previousSyncCtx != thread._synchronizationContext)
+                {
+                    thread._synchronizationContext = previousSyncCtx;
+                }
 
-            ExecutionContext? currentExecCtx = thread._executionContext;
-            if (previousExecCtx != currentExecCtx)
-            {
-                ExecutionContext.RestoreChangedContextToThread(thread, previousExecCtx, currentExecCtx);
+                ExecutionContext? currentExecCtx = thread._executionContext;
+                if (previousExecCtx != currentExecCtx)
+                {
+                    ExecutionContext.RestoreChangedContextToThread(thread, previousExecCtx, currentExecCtx);
+                }
             }
         }
 
-        private static void CaptureContinuationContext(SynchronizationContext syncCtx, ref object context, ref ContinuationFlags flags)
+        private static void CaptureContinuationContext(ref object continuationContext, ref ContinuationFlags flags)
         {
+            SynchronizationContext? syncCtx = Thread.CurrentThreadAssumedInitialized._synchronizationContext;
             if (syncCtx != null && syncCtx.GetType() != typeof(SynchronizationContext))
             {
                 flags |= ContinuationFlags.ContinueOnCapturedSynchronizationContext;
-                context = syncCtx;
+                continuationContext = syncCtx;
                 return;
             }
 
             TaskScheduler? sched = TaskScheduler.InternalCurrent;
             if (sched != null && sched != TaskScheduler.Default)
             {
                 flags |= ContinuationFlags.ContinueOnCapturedTaskScheduler;
-                context = sched;
+                continuationContext = sched;
                 return;
             }
 

src/coreclr/inc/clrconfigvalues.h

@@ -714,7 +714,7 @@ RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableRiscV64Zbb,             W("EnableRiscV64
 #endif
 
 // Runtime-async
-RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 0, "Enables runtime async method support")
+RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 1, "Enables runtime async method support")
 
 ///
 /// Uncategorized

src/coreclr/inc/corinfo.h

@@ -722,6 +722,7 @@ enum CorInfoOptions
                                                CORINFO_GENERICS_CTXT_FROM_METHODDESC |
                                                CORINFO_GENERICS_CTXT_FROM_METHODTABLE),
     CORINFO_GENERICS_CTXT_KEEP_ALIVE        = 0x00000100, // Keep the generics context alive throughout the method even if there is no explicit use, and report its location to the CLR
+    CORINFO_ASYNC_SAVE_CONTEXTS             = 0x00000200, // Runtime async method must save and restore contexts
 };
 
 //