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Bug 623635 - [annotation] Add begin/finish annotations for GAsyncResult
[annotation] Add begin/finish annotations for GAsyncResult
Product: gobject-introspection
Classification: Platform
Component: general
Other Linux
: Normal enhancement
: ---
Assigned To: gobject-introspection Maintainer(s)
gobject-introspection Maintainer(s)
Depends on:
Reported: 2010-07-05 21:28 UTC by Travis Reitter
Modified: 2018-02-08 11:55 UTC
See Also:
GNOME target: ---
GNOME version: ---

Description Travis Reitter 2010-07-05 21:28:17 UTC
Some languages (like Vala) support native syntax for asynchronous functions.

Vala's GLib/C parser has a heuristic that treats pairs of functions with signatures

void    $(foo)_async (..., GAsyncResultCallback cb, ...);
$(type) $(foo)_finish (..., GAsyncResult *res, ...);

as a native async function returning type $(type).

In order for Vala's (and other languages') GIR parser to generate the same binding, without having to hard-code this heuristic, g-ir-scanner/compiler will need to implement it and adjust GIR output accordingly.
Comment 1 André Klapper 2015-02-07 17:21:49 UTC
[Mass-moving gobject-introspection tickets to its own Bugzilla product - see bug 708029. Mass-filter your bugmail for this message: introspection20150207 ]
Comment 2 Philip Chimento 2017-01-26 22:31:06 UTC
Future versions of Javascript will gain native syntax for this as well, I would expect that to land in GNOME 3.26.
Comment 3 Emmanuele Bassi (:ebassi) 2017-09-15 11:40:24 UTC
Rust is also interested in this, so I think we have critical mass for a new annotation, and possibly some heuristic.
Comment 4 Sebastian Dröge (slomo) 2017-09-15 11:47:29 UTC
As a heuristic, this should work for the cases that I saw so far:

If there is a xxx_finish() function with a GAsyncResult parameter, check
  a) Is there a xxx_async() function with a GAsyncResultCallback parameter, or
  b) Is there a xxx() function with a GAsyncResultCallback parameter

b) is the case for various GDBus functions where the sync variant is called xxx_sync() instead.

One might also want to annotate which function is the sync variant, if any.
Comment 5 Emmanuele Bassi (:ebassi) 2017-09-15 11:53:47 UTC
Let's start the bikeshed.

We should use a function-level annotation, e.g.

   * foo_bar_decide_async: (async-finish foo_bar_decide_finish):
   * @self: a #FooBar
   * @blah: a #FooBlah
   * @cancellable: (nullable): a #GCancellable
   * @callback: a #GAsyncResultCallback
   * @data: data to pass to @callback
   * ...

This also works for functions that are asynchronous but have no '_async' modifier (e.g. GDBus):

   * foo_bar_collect: (async-finish foo_bar_collect_finish):
   * ...

These would be translated into the GIR as an attribute to the callable elements — function, method, virtual-method, e.g.

  attribute async-finish { xsd:string }?

The heuristics for automatically detecting this in the scanner would be:

  - the callable has a GAsyncResultCallback argument
    - if the callable ends with '_async', remove that token
    - check if function_name + '_finish' exists in the same namespace
    - check if function_name + '_finish' has a GAsyncResult argument

This should keep the false positives to zero.
Comment 6 Sebastian Dröge (slomo) 2017-09-15 12:42:42 UTC
I like the color of your bikeshed. Maybe in addition having a way of linking the sync version of a function to the async one, and the other way around, would be useful. But I can only think of it being useful for documentation purposes right now.
Comment 7 Philip Chimento 2017-09-19 04:23:49 UTC

Here's Vala's heuristic:

Looks like exactly the same.
Comment 8 Antoni 2017-11-12 17:18:22 UTC
I found this function:

That has a `_finish` method that requires an annotation because the `_finish` method has a different prefix (no `_bytes`).
Comment 9 GNOME Infrastructure Team 2018-02-08 11:55:46 UTC
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