Avoid pinning OverlappedData objects

[preetamshetty1]

NativeOverlapped moved the data to native memory. The code below creates an AsyncPinned handle for the object and consequently the userData. Can we consider avoiding the pinning here? Or move these to the POH?

The handle right now does contribute to fragmentation. Especially for cases where there may be long running connections etc. which may promote these to GEN2.

overlappedHolder->m_handle = GetAppDomain()->CreateTypedHandle(overlapped, HNDTYPE_ASYNCPINNED);

HandleTable:
0000023FD9E5A950 (async pinned handle)
-> 0000023FB8978590 System.Threading.OverlappedData

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[preetamshetty1]

The GC will ignore these objects as suggested in

runtime/src/coreclr/vm/gcenv.ee.cpp

Lines 1521 to 1558 in 9d6396d

	void GCToEEInterface::WalkAsyncPinnedForPromotion(Object* object, ScanContext* sc, promote_func* callback)
	{
	LIMITED_METHOD_CONTRACT;
	assert(object != nullptr);
	assert(sc != nullptr);
	assert(callback != nullptr);
	if (object->GetGCSafeMethodTable() != g_pOverlappedDataClass)
	{
	// not an overlapped data object - nothing to do.
	return;
	}
	// reporting the pinned user objects
	OverlappedDataObject *pOverlapped = (OverlappedDataObject *)object;
	if (pOverlapped->m_userObject != NULL)
	{
	if (pOverlapped->m_userObject->GetGCSafeMethodTable() == g_pPredefinedArrayTypes[ELEMENT_TYPE_OBJECT].AsMethodTable())
	{
	// OverlappedDataObject is very special. An async pin handle keeps it alive.
	// During GC, we also make sure
	// 1. m_userObject itself does not move if m_userObject is not array
	// 2. Every object pointed by m_userObject does not move if m_userObject is array
	// We do not want to pin m_userObject if it is array.
	ArrayBase* pUserObject = (ArrayBase*)OBJECTREFToObject(pOverlapped->m_userObject);
	Object **ppObj = (Object**)pUserObject->GetDataPtr(TRUE);
	size_t num = pUserObject->GetNumComponents();
	for (size_t i = 0; i < num; i++)
	{
	callback(ppObj + i, sc, GC_CALL_PINNED);
	}
	}
	else
	{
	callback(&OBJECTREF_TO_UNCHECKED_OBJECTREF(pOverlapped->m_userObject), (ScanContext *)sc, GC_CALL_PINNED);
	}
	}
	}

. Closing this specific request.