How to get the name of an Event from a handle

Question

I have an array of Win32 event handles that I'm waiting on using WaitForMultipleObjects(). This returns the index in the array of events that triggered but what I need to know is the name of the event. I've been looking through MSDN and can't see anything to do this.

Basically I have a class that monitors the registry through events using RegNotifyChangeKeyValue() for a defined period of time but before it starts other classes register there interest in keys and values. I then wait on a separate thread and report back the name of the keys that have been modified. The event name is the key that the event is for and I don't know until runtime how many of these there will be or what they will be called. I don't want to create one thread per key as it's not very performant.

Does anyone know how to get the event name or a better way of doing this?

Answer 1

Personally I wouldn't do it that way. Create your own mapping (std::map?) between event and key name and then do your own lookup when an event is signalled.

Answer 2

You could probably do it with undocumented NT stuff, maybe NtQueryObject(handle,ObjectNameInformation,....)

Answer 3

Normally the name of an event is used to call OpenEvent() to get the Handle. This way, you don't need to communicate a handle at runtime, but instead settle on a naming convention for the name of the event.

I can think of three ways to do this:

• Loop over all hard-coded event names and call OpenEvent()
• Save the handles and names in an std::map
• Create a class to store your handles and names (possibly in an std::map), and write methods to quickly get a name from a handle.

Are you deciding what actions to take based on the name of the event? An 'if else if' statement that checks the names of the handles one-by-one to determine what action to take? This kind of scenario usually leads me to consider inheritance as a potential solution. Bear with me for a bit.

What if you create a base class, say EventAction. This has a handle to an event, and a virtual member function go_go_commandos(). You derive from it for each 'event' that has an action to be taken, and implement the action in the go_go_commandos() method of each deriving class.

Now what you need is a container so you can say actionlist->GetEventAction( handle )->go_go_commandos().

Did that help at all?