Errors and the introspection format
thiago.macieira at trolltech.com
Tue Feb 21 01:53:43 PST 2006
Havoc Pennington wrote:
>Possibly the NoReply annotation should have been GLib.NoReply, and
>separately we should have a Qt.Async to match the DCOP-compat kind of
>feature done in Qt bindings which is slightly different; this would also
>help clarify that NoReply is just about bindings and code generation,
>not about any intrinsic property of an interface or the wire protocol.
No, they're the same thing.
As I explained in the other email, the term "async" is being abused
for "no-reply" because of DCOP compaibility (i.e., old misnomer). It
means "the function will still be executing while control has returned to
you". It's not an asynchronous call in the sense of DBusPendingCall
callbacks -- which, in the original Qt binding implementation, was
But, as you suggested, here are a few use-cases to clarify:
I'd say this is a normal call. While the music player will take some time
to load, you want to know whether the launching was successful. So this
method would be have one output argument indicating success.
Again, normal call. This would be a really slow call, so its return value
will take some time to happen. Since this is really exceptional, the
caller should know what it is doing, set the timeouts higher and place an
asynchronous (DBusPendingCall) call, so that it'll get the reply
hopefully sometime before the next century.
* ReloadConfiguration: (a.k.a. SIGHUP)
You just want to make it reload the configuration: there's no success or
not. This would be a candidate for the NoReply annotation.
When a caller tries to place a call to this function, it should see the
annotation and SHOULD use "fire-and-forget" (DCOP "async") mode.
If the caller did not set the noreply flag in the call message, the callee
MUST return a reply. In this case, it'll be an empty success reply every
time if the method was called, or an error if it couldn't.
Like CalculatePI, this is a lengthy operation. However, given the number
of possible different outcomes and given the fact that the application
will probably want to show some progress bars, estimated time and
possibly even start to render the file while its download in progress,
I'd say this is a real asynchronous function with special circumstances:
all the replies will be handled through Method "Callbacks" back to the
user application. It should return ASAP a handle indicating the context,
which will be used all the callbacks. But the real download will start
later and you won't know if the _download_ succeeded until much later.
So, I'd say the input parameters for a DownloadFile function would be the
URL of the file to download and the service + path of the callback object
(interface and methods would be standardised elsewhere). We'd have
methods like "Data" for data being received, "MetaData" to receive (for
instance) headers, "Finished" to signal completion or "Error" if
something weird happens.
Thiago José Macieira - thiago.macieira AT trolltech.com
Trolltech AS - Sandakerveien 116, NO-0402 Oslo, Norway
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