Re: [Vala] Thread Support

[Daniel Espinosa <esodan gmail com>]

Thanks for your comments and suggestions.


2014-08-13 14:02 GMT-05:00 Jim Nelson <jim yorba org>:

> On Wed, Aug 13, 2014 at 10:55 AM, Daniel Espinosa <esodan gmail com>
> wrote:
>
> I have an async function called directly in my code. When compiles I get
> this: XXXXXXX: warning: implicit .begin is deprecated
>
>
> That means you called the async method with neither a yield keyword nor
> with the begin modifier.  You need to do either this:
>
> yield read_async();
This form is not documented in Vala Manual. I'll add it. This seems to be
more convenient for reading, the second could be read as "an object
read_async have a method called begin() and it is called", but the first
means: "you call a function read_async() and yields it up to finish it".
I'll use the first form in my code.



> or this:
>
> read_async.begin();

For the comment above, I think this form must be deprecated to add clear
meaning in Vala code for async functions, even the compiler must rise an
error when yield is used in unasync function.


> Vala used to support:
>
> read_async()
>
> as being equivalent to using .begin(), but that form was deprecated, hence
> the message you're seeing.
>
> Thread<void> th = new Thread<void>.try ("loading scl", () => {
> async_function (); /*Asinc function */ return null; }); th.join (); Error
> message is: XXXXX: error: The name `try' does not exist in the context of
> `GLib.Thread' I've checked glib-2.0.vapi, for both vala-0.20 and 0.22, that
> function is present just for GLIB_2_32, checking my installed version I
> have a 2.40 on a GNOME Ubuntu 14.04 box.
>
>
> Add this flag to valac:
>
> --target-glib=2.40
>
> or:
>
> --target-glib=2.32
>
> Be aware by doing this you're making your app incompatible with earlier
> versions of glib.

Then this is a bug in glib-2.0.vapi, because it seds:

[Deprecated (since = "2.32", replacement = "new Thread<T> ()")]
[CCode (simple_generics = true)]
public static unowned Thread<T> create<T> (ThreadFunc<T> func, bool
joinable) throws ThreadError;

Then this makes compiler to throws a warning each time you don't use
--target-glib=2.32 or some thing, and this is a mistake because you are
using "generic" code, if I use Thread<T>.try I'm making back incompatible
code.

If I follow compiler warning to replace deprecated code, I found the
problem above, then defining GLIB_2_32 must be present by default or even
better modify to glib-2.0.vapi to help the developer how to proceed:

[Deprecated (since = "2.32", replacement = "new Thread<T> () and valac's
--target-glib=2.32 flag")]
[CCode (simple_generics = true)]
public static unowned Thread<T> create<T> (ThreadFunc<T> func, bool
joinable) throws ThreadError;



> Regarding your code itself, there's a few more problems.  First, you can't
> use <void> as a type parameter, you must give an actual type that
> represents storage.  "void *" is probably the best way to go if you truly
> have nothing to pass to your threads.

Your explanation is a good point to be added to Vala's Manual.


> Second, you're calling an async method within the background thread.
>  There's nothing technically wrong with this, but I suspect that's not what
> you really want.  The usual pattern of use is to call the async method from
> your main ("foreground") thread.  The async call might use background
> threads as an implementation strategy (to do the work without blocking the
> foreground thread).
>
> -- Jim

You're right, I've changed to

async_function.begin ()

and I've removed Thread, but now I'll use

yield async_function().

for better understanding.

Warning from compiler must suggest to use this instead to just warn about
use implicit .begin is deprecated. Message could be:

"async functions should use attribute .begin or 'yield' modifier when it is
called"

-- 
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