Thread

callbacks (Sdk)

callbacks // Sdk

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jan-willem de bleser

Oct 3, 1998, 5:02pm
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Ok. Ive looked over all the docuentation but i still cant figure out
what a callback is. can someone explain to me what it is and how to use
it?

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jeanphi

Oct 4, 1998, 8:17am
Hi,

If I well understood, the callbacks are functions that allow you to get info
from the server.

like aw_world list_list seems to send you the list of worlds running on the
universe you are in.

jeanphi

netropolis

Oct 4, 1998, 10:05am
Basically, a callback is a function pointer which is used to call a
function. Check the following code...

/* pointer to a function */
void (*afunction)(int);

/* callback installer */
void set_callback(void (*acallback)(int)) { afunction = acallback; }

/* callback caller */
void call_callback(int a) { afunction(a); }

/* function to install as a callback */
void mycallback(int a)
{
printf("a=%d\n", a);
}

void main(void)
{
set_callback(mycallback);
call_callback(1);
}

This is a generic example to show how callbacks work, too much work just
to print "a=1" :))

Using the AW SDK, you don't have to implement the "set_callback" and
"call_callback" functions. You have to write the function that will be
installed as callback using "aw_callback_set", the SDK is responsible
for calling it.

Check http://www.activeworlds.com/sdk/asynchro.htm

HTH,

-Netro

jan-willem de bleser

Oct 5, 1998, 7:10pm
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but the function returns the info itself. i reread it a few times and it seems
like you can tell the function to return before it is done so you can continue
the rest of the program. the data is then recieved later.

[View Quote] > Hi,
>
> If I well understood, the callbacks are functions that allow you to get info
> from the server.
>
> like aw_world list_list seems to send you the list of worlds running on the
> universe you are in.
>
> jeanphi



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n: De Bleser;Jan-willem
org: High school
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--------------6E497948E93E4073BCF2125C--

edward sumerfield

Oct 7, 1998, 12:23am
There is practically no difference between callbacks and aw_event_set
functions. Its just a way for the SDK to call your code.

I don't understand why the SDK implements them using different mechanisms.

Netropolis said it all.

Edward Sumerfield.

[View Quote]

roland vilett

Oct 7, 1998, 2:41pm
>There is practically no difference between callbacks and aw_event_set
>functions. Its just a way for the SDK to call your code.
>
>I don't understand why the SDK implements them using different mechanisms.


There is a conceptual difference. Callbacks occur in order to report the
results to you of specific actions that your app has triggered, e.g. adding
an object, looking up a citizen, etc. Success or failure of the request is
common to all callbacks, thus the callback functions take a single int rc
argument. Meanwhile, events can happen at any time, not necessarily in
response to your application's actions. They don't have a concept of
succeeding or failing, thus the event handlers do not take any arguments.

-Roland

jan-willem de bleser

Oct 7, 1998, 7:09pm
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Roland, can you please slowly explain how to use callbacks and where to use
them?

[View Quote] >
> There is a conceptual difference. Callbacks occur in order to report the
> results to you of specific actions that your app has triggered, e.g. adding
> an object, looking up a citizen, etc. Success or failure of the request is
> common to all callbacks, thus the callback functions take a single int rc
> argument. Meanwhile, events can happen at any time, not necessarily in
> response to your application's actions. They don't have a concept of
> succeeding or failing, thus the event handlers do not take any arguments.
>
> -Roland



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org: High school
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roland vilett

Oct 7, 1998, 11:06pm
I did the best job I can do of explaining callbacks in the "Asynchronous
Operation" section of the SDK docs:

http://www.activeworlds.com/sdk/asynchro.htm

-Roland

[View Quote]

jan-willem de bleser

Oct 7, 1998, 11:32pm
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whats Asynchronous Operation?

[View Quote] > I did the best job I can do of explaining callbacks in the "Asynchronous
> Operation" section of the SDK docs:
>
> http://www.activeworlds.com/sdk/asynchro.htm
>
> -Roland
>
[View Quote]

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n: De Bleser;Jan-willem
org: High school
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edward sumerfield

Oct 8, 1998, 2:07am
Time to take a programming coarse.

Synchronous operation is one thing after another.
Asynchronous operation is many things at once.

Well, kind of. Lets use a little bit of psuedo code.

Sync operation:

while do forever

do this thing and wait
done

Async operation:

while do forever

do this thing and while it is doing it return.

/* so the thing is still goint but this code is continuing anyway.
*/

do another thing.
done

How about an example.

You want to read a message from a communications line. You can call a read
function and wait for data to arrive at your machine, sync operation. Or you
can call a read function to indicate that you wand date but then return. Now
while you are waiting for data to arrive you can be doing something else.
When the data arrives the other part of your program calls you.

I think I may be making things more complicated than they need to be. Sorry.

The aw sdk.

aw_callback_set(function);
aw_query
while ()

do something.
}

function() {

this will be called when the query operation is complete.
}

You know, if you don't need to get into higher efficiency bots I would just
ignore the issue.

Edward Sumerfield.

[View Quote]

jan-willem de bleser

Oct 8, 1998, 9:19am
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actually, you helped. thanks

[View Quote] > Time to take a programming coarse.
>
> Synchronous operation is one thing after another.
> Asynchronous operation is many things at once.
>
> Well, kind of. Lets use a little bit of psuedo code.
>
> Sync operation:
>
> while do forever
>
> do this thing and wait
> done
>
> Async operation:
>
> while do forever
>
> do this thing and while it is doing it return.
>
> /* so the thing is still goint but this code is continuing anyway.
> */
>
> do another thing.
> done
>
> How about an example.
>
> You want to read a message from a communications line. You can call a read
> function and wait for data to arrive at your machine, sync operation. Or you
> can call a read function to indicate that you wand date but then return. Now
> while you are waiting for data to arrive you can be doing something else.
> When the data arrives the other part of your program calls you.
>
> I think I may be making things more complicated than they need to be. Sorry.
>
> The aw sdk.
>
> aw_callback_set(function);
> aw_query
> while ()
>
> do something.
> }
>
> function() {
>
> this will be called when the query operation is complete.
> }
>
> You know, if you don't need to get into higher efficiency bots I would just
> ignore the issue.
>
> Edward Sumerfield.
>
[View Quote]

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begin: vcard
fn: Jan-willem De Bleser
n: De Bleser;Jan-willem
org: High school
email;internet: debleser at mediaone.net
x-mozilla-cpt: ;0
x-mozilla-html: FALSE
version: 2.1
end: vcard


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