Cannot tick() recursively; event reactor already active about amp HOT 11 CLOSED

In case you like to wait "synchronously" for a promise, just yield it.

\Amp\run(function() {
    $promise = \Amp\Dns\resolve('google.ca');
    $result = yield $promise;
    var_dump($result);
});

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@staabm He knows that…

By the way, your icicle example works as expected (or not?) as it does not wait on the same loop, but once on the icicle loop, once on the amp loop.

The main issue with wait() inside already async context is that it leads to heavy recursion which may or may not fail depending on whether a certain generator is already in your stack trace (cannot resume a current running Generator). It's a large pitfall which may only happen in more complex applications.
Also, the VM only continues after a wait() if all calls afterwards to wait() are resolved (due to the way stacktraces work. That's what we have Generators for!).

Thus we forbid this explicitly. You have to yield Promises or yield from Generators. That's an inherent requirement which we cannot lift without making Amp very unstable.

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Surprisingly, my icicle example works great. Amp\Dns\Resolve yields just fine inside the Icicle loop.

I can't leverage yield, becaus yield isn't allowed in the same function with a return. And I can't pass promises up the entire stack where the Amp context is created because I have a middle layer I don't want to change. So unless I'm missing something, its impossible to use a generator inside an \Amp\wait() context, which is the heart of my issue.

IE this is not allowed:

\Amp\run(function() {
    function resolve() {
        $promise = \Amp\Dns\resolve('google.ca');
        $result = (yield $promise);
        return ($result);
    }
    var_dump(resolve());
});

PHP Fatal error: Generators cannot return values using "return"

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Looks like you are using PHP 5.

In this case you may yield new \Amp\CoroutineResult($result); instead of a return.

P.s.: that icicle works great is that you example is so simple and you are effectively using two different loops here. In your problematic gist, it's all one same loop, thus problematic.

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That doesn't work either. It just moves the problem.

\Amp\run(function() {
    function resolve() {
        $promise = \Amp\Dns\resolve('google.ca');
        $result = (yield $promise);
        yield new \Amp\CoroutineResult($result);
    }
    $generator = resolve();
    // cant wait:
    \Amp\wait(\Amp\resolve($generator));
   // can't (yield resolve()); because then I can't return to my parent which is synchronous
});

I can't figure out how to use yield where inside the call stack there is a return that waits synchronously inside an Amp context. :) omg my head hurts.

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@chrisleavoy It's not possible. You can't do it with the middle being unaware of promises.

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oh, you want to explicitly run synchronously (i.e. block everything else possibly waiting? right?).

In this case you have to replace the reactor around that:

$old = \Amp\reactor();
\Amp\reactor(\Amp\driver())
$result = \Amp\wait(resolve());
\Amp\reactor($old);

from amp.

Thats not quite what I need. In my example gist, (updated: https://gist.github.com/chrisleavoy/9c2386e3b408399c4ba2e5a4db055888) I'll have 4 or more parallel "plugins" running asynchronously. Each plugin has a synchronous function and waits for the underlying DNS query, which should yield in the outer Amp reactor letting other plugins run when ready. If I create multiple Amp reactors, the yield doesn't work. In my Icicle example (https://gist.github.com/chrisleavoy/18b4032402d7b2d7f688655fe28eab60) parallel Amp\waits inside one outer Icicle reactor, seems to work. Ideally I'd like to get this working without Icicle though.

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https://gist.github.com/bwoebi/7cba5729647b7ee76fcc337a06e0a5ed

You must keep your functions async between each other. You must call Amp\wait() only outside the async tree.
There is no way around that; this is inherent to Amp and Icicle.

Your Icicle/Amp mix just seems to work now, but it will fail in much more complicated setups.

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Darn.

Thanks so much for the schooling. Much appreciated. I was really trying not to chain the entire call stack but it sounds like its not possible. On closer debugging, my Iclcle/Amp mix, wasn't actually async. I had only made it so overly complicated that I wasn't tracing it properly. 😆

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No problem, people who have coded always sync before all have similar problems...

Happy to help out and make you understand the concepts properly!

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