Re: [boost] [rfc] rcpp

Subject: Re: [boost] [rfc] rcpp
From: Daniel Trebbien (dtrebbien_at_[hidden])
Date: 2010-02-28 14:41:13

> What kind of HANDLE that can be returned from DuplicateHandle should not  
> be disposed by CloseHandle?

The only time I should call `CloseHandle` on the `HANDLE` result from  
`DuplicateHandle` is if the `DuplicateHandle` call succeeded. This is  
because the MSDN documentation does not assert that the `HANDLE` resulting  
 from `DuplicateHandle` will never be `NULL` or `INVALID_HANDLE_VALUE`.

>> Essentially the underlying resource type in this case
>> is a pair of a `HANDLE` and `BOOL`, where the "invalid value" is a
>> pair with the `BOOL` set to `FALSE` and an indeterminate value of the
>> `HANDLE`. In order to use the `rcpp::resource` template, I would need
>> to override the `==` operator so that equality of the resource means
>> equality of the `BOOL` member only, which is not ideal. I think that
>> an `is_invalid` member would do the trick rather nicely, however.
> Why do not use boost::optional<HANDLE> as underlying resource type?

I hadn't thought of this. Seems like it would work...

>> Also, I think that it would be nice to have a `shared_resource`
>> template. I have an application in mind where I would like to create a
>> shared `HANDLE` that is only closed if it is invalid and all
>> references to it have been destroyed (a shared reference count reaches
>> 0).
> I thought about that. I don't think it has wide application. Moreover it  
> can be emulated with boost::shared_ptr<rcpp::resource>. Is it worth  
> while?

I think so because `boost::shared_ptr` adds a level of indirection that is  
unnecessary.