The COM enumerator does not call VCOMM to detect COM devices, rather it writes directly to the port. When called to enumerate a device on a COM port, COMENUM calls ACQUIRE_RESOURCE with ACQUIRE_NO_STEAL, so that it does not inadvertently interfere with another program using the port.
The COM enumerator always returns TRUE for RESOURCE_STEAL_REQUEST.
When it receives a RESOURCE_RETURN_NOTIFY, the enumerator resumes its watch COM device attach/detach on the port.
The COM enumerator never calls RELEASE_RESOURCE.