[openbeosstorage] Re: Registrar-Based Notification Mechanism
- From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
- To: openbeosstorage@xxxxxxxxxxxxx
- Date: Tue, 18 Feb 2003 18:16:17 +0100 CET
"Ingo Weinhold" <bonefish@xxxxxxxxxxxxxxx> wrote:
[...]
> > Why is that=3D3F Why should the hook approach make it necessary to
> > prepare
> > the data that has to be written to the ring buffer while the
> > "direct"
> > approach wouldn't=3D3F
> That may depend on the implementation. Assuming that you have a
> notification=5Fevent structure, that shall contain the relevant data in
> a
> flattened form, and the hook functions of the subscribers shall be
> called with a pointer to such a structure, then, obviously the data
> need to be copied into that structure before the hooks can be called.
> Unless, and that is maybe what you are referring to, the structure
> does
> already exist anyway and thus doesn't need to be composed for that
> purpose -- then there is no extra overhead.
>
> But if you have to fill in such a structure -- you do perhaps
> allocate
> it on the stack -- then this structure has to be copied into the ring
> buffer by the hook responsible for the registrar communication in a
> second step. While, otherwise, without the kernel hooks, the function
> would allocate space in the ring buffer and fill in the data
> directly.
Ah yes, now I understand what you meant, thanks!
[...]
> > Ah, yes, I see, so it should provide a Flatten() call that already
> > defines the target handler - something it has to provide internally
> > anyway. That should be very easy to do.
> No, that's not what one would want. Setting the target of a BMessage
> (fTarget, fPreferred) can easily be done now using the friend
> function
> =5Fset=5Fmessage=5Ftarget=5F(). The point is to flatten the message only once
> and for each target set the respective handler in the flattened data.
> I
> could imagine a private `static status=5Ft
> BMessage::SendFlattened(const
> void *data, size=5Ft size, BMessenger target,...)' that sets the target
> in the flattened data and sends it to the respective port.
Again, you thought more than me... :-))
Sure, that's exactly what one would want to have, but that again, would
be easy to do, once BMessage is in place. Just a friend method that
sets the target and calculates the checksum to complete the flattened
buffer - that can be used by Flatten(), too (but only once, there).
Adios...
Axel.
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