Hi,
here is something that has been puzzeling me (and that may just be
because I have misunderstood something trivial): I have read that
JavaScript interpreters are usually single threaded. A page on
supported language features seems to imply that for this reason, GWT
doesn't not honor the synchronized keyword and does not provide any
other locking mechanisms. Also of course you can't create more threads
as you would in a normal Java application.
Not that I would want to do that but what I'm wondering is when the
Callbacks of AJAX calls are served. If they are served right away that
would be like introducing another thread and would in some cases
introduce the need for mutexes.
Here is a concrete example: I have a call that, say, fetches a String
Foo. Foo is needed at a few places in my program, so I write a Proxy
method that will cache Foo so it is only fetched once. So on a call of
that method it will check if Foo is in the cache and if not make the
AJAX call (the method will also 'return' Foo via an AsyncCallback).
This implementation will of course still fetch Foo multiple times,
since the method will likely have been called more than once before
the AJAX call returns and can cache the value of Foo. So what I would
like to do is for my Proxy method, to store a list of requests for
example like so:
private List<AsyncCallback<String>> callbacks = new ...;
private String foo;
public FooProxy {
MyServiceAsync.getFoo(new AsyncCallback() {
/* On Success, cache the value in foo and notify all callbacks */
});
}
public void getFoo(AsyncCallback<String> callback) {
if(foo != null) callback.onSuccess(foo);
else callbacks.add(callback);
}
But if the callback from MyServiceAsync.getFoo can interrupt a call to
getFoo at any time, this is clearly not 'thread safe'. However without
any language support, I don't think it can be made so...
Am I making any false assumptions here? Is there any other obvious way
of achieving the desired effect?
Thanks,
Johannes
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