Re: async code and the callback-chain
Daniel, First thing, With Asynchronous call you should never get the Stack over flow as Asynchronous calls are running in different thread and your function retursn back before calls finish. But i think you have genuine problem of asynchronous call chains...where writing code become too problematic. I had the same issue and long back i started this discussion that having synchronous calls will be a good idea too., so that you don't need to write async callback and leave it up to the developer if they want to use synchronous calls. But that time then i had to create a single class with one boolean variable for each kind of call and correpsonding data. So whenevr a call finishes i call the function of that class as MySIngleTonCLass.setLoginCallFNished(true) MySIngleTonCLass.setUser(User) MySIngleTonCLass.refresh(); if some other class finishes then i call something like MySIngleTonCLass.setDataRetrivedCall1(true) MySIngleTonCLass.setDataRetrived1(someData) MySIngleTonCLass.refresh(); MySIngleTonCLass.setDataRetrivedCall2(true) MySIngleTonCLass.setDataRetrived2(someData2) MySIngleTonCLass.refresh(); and then had to write my login in MySIngletonClass to update UI. ( my problem area was updating the UI) so i do something like if(getLoginCallFNished() and user != null) create Logout Link else create loginLink if(getDataRetrivedCall1() and data1!= null) Display the Data else Display No Data found So yopu need to see if such kind of solution will fir to your problem. But definitely asynchrnous call WILL not give you stack overflow. It must be your code somewhere. Ravi On Jun 12, 2:14 pm, daniel d.brelov...@googlemail.com wrote: hi all, I hope someone can help to find a solution to the following problem: I have some complex code that may need data from the server. When I make a request I get the data asynchronous, so I have to provide a callback to handle the response. Now all the code that use this function need a callback too. But this leads to very long chains of nested callbacks. Especially when I need to call async methods in a loop and every call may depend on the previous, I can`t find a way to do this without calling the method recursive in the onSuccess of the callback. But this way I get a StackOverflow very fast. I can`t request all data first and run the code that needs it after that, cause which data is needed may depend on the data I already got. I have really no idea - hopefully you have thx in advance --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Re: async code and the callback-chain
Hi Ravi,
thanks for your reply.
You`re right. ts not the async call itself that leads to the
stackoverflow. its because of the callback chain that comes when a
large amount of code depends directly or indirectly on the callback.
supposed i have some simple code like this:
public Value doSomething(Value v){
Value newV = getValue();
//do something with the values
//e.g. add them
return newV.add(v);
}
public Value execute(){
Value v1 = getValue();
Value v2 = doSomething(v1);
Value v3 = doSomesting(v2);
return doSomething(v3);
}
everything is fine with this... but when i decide that getValue()
should request the Value from the Server i have to rewrite the code
to:
private void doSomething(final Value v, final AsyncCallbackValue
callback){
getValue(new AsyncCallbackValue(){
public void onSuccess(Value result) {
//do something with the values
//e.g. add them
callback.onSuccess(result.add(v));
}
public void onFailure(Throwable caught) {
callback.onFailure(caught);
}
});
}
public void execute(final AsyncCallbackValue callback){
getValue(new AsyncCallbackValue(){
public void onSuccess(Value result) {
doSomething(result, new AsyncCallbackValue(){
public void onSuccess(Value result) {
doSomething(result, new
AsyncCallbackValue(){
public void onSuccess(Value
result) {
doSomething(result, new
AsyncCallbackValue(){
public void
onSuccess(Value result) {
callback.onSuccess(result);
}
public void
onFailure(Throwable caught) {
callback.onFailure(caught);
}
});
}
public void onFailure(Throwable
caught) {
callback.onFailure(caught);
}
});
}
public void onFailure(Throwable caught) {
callback.onFailure(caught);
}
});
}
public void onFailure(Throwable caught) {
callback.onFailure(caught);
}
});
}
of course i would not write such code, but it illustrates the problem.
The chain of callbacks gets longer with every call to doSomething.
Imagine it should be called in a loop for 100 times or more ... than a
stackoverflow occures. And even if getValue doesn`t need to aks the
server every time (maybe most values are cached on clientside) the
code must be written in this way. I can reduce the amount of written
code by providing a recursive method for such calls, but i don't find
a way to get rid of the callback chain.
On 12 Jun., 18:06, Ravi ping2r...@gmail.com wrote:
Daniel,
First thing, With Asynchronous call you should never get the Stack
over flow as Asynchronous calls are running in different thread and
your function retursn back before calls finish.
But i think you have genuine problem of asynchronous call
chains...where writing code become too problematic.
I had the same issue and long back i started this discussion that
having synchronous calls will be a good idea too., so that you don't
need to write async callback and leave it up to the developer if they
want to use synchronous calls.
But that time then i had to create a single class with one boolean
variable for each kind of call and correpsonding data.
So whenevr a call finishes i call the function of that class as
MySIngleTonCLass.setLoginCallFNished(true)
MySIngleTonCLass.setUser(User)
MySIngleTonCLass.refresh();
if some other class finishes then i call something like
MySIngleTonCLass.setDataRetrivedCall1(true)
MySIngleTonCLass.setDataRetrived1(someData)
MySIngleTonCLass.refresh();
MySIngleTonCLass.setDataRetrivedCall2(true)
MySIngleTonCLass.setDataRetrived2(someData2)
MySIngleTonCLass.refresh();
and then had to write my login in MySIngletonClass to update UI. ( my
problem area was updating the UI)
so i do something like
if(getLoginCallFNished() and user != null)
