Breaking out of a Gearman loop - php

Question

I have a php application that gets requests for part numbers from our server. At that moment, we reach out to a third party API to gather pricing information to make sure we have the latest pricing for that particular request. Sometimes the third party API is slow or it might be down, so we have a database that stores the latest pricing requests for each particular part number that we can use as a fallback. I'd like to run the request to the third party API and the database in parallel using Gearman. Here is the idea:
Receive request
Through gearman, create two jobs:
Request to third party API
MySQL database lookup
Wait in a loop and return the results based on the following conditions:
If the third party API has completed return that result, return that result immediately
If an elapsed time has passed, (e.g. 2 seconds) and the third party API hasn't responded, return the MySQL lookup data
Using gearman, my thoughts were to either run the two tasks in the foreground and break out of runTasks() within the setCompleteCallback() call, or to run them in the background and check in on the two tasks within a separate loop and check in on the tasks using jobStatus().
Unfortunately, I can't get either route to work for me while still getting access to the resulting data. Is there a a better way, or are there some existing examples of how someone has made this work?

Answer 1

I think you've described a single blocking problem, namely the results of an 3rd-party API lookup. There's two ways you can handle this from my point of view, either you could abort the attempt altogether if you decide that you've run out of time or you could report back to the client that you ran out of time but continue on with the lookup anyway, just to update your local cache just in case it happens to respond slower than you would like. I'll describe how I would go about the former problem because that would be easier.
From the client side:
$request = array(
'productId' => 5,
);
$client = new GearmanClient( );
$client->addServer( '127.0.0.1', 4730 );
$results = json_decode($client->doNormal('apiPriceLookup', json_encode( $request )));
if($results && property_exists($results->success) && $results->success) {
// Use local data
} else {
// Use fresh data
}
This will create a job on the job server with a function name of 'apiPriceLookup' and pass it the workload data containing a product id of 5. It will wait for the results to come back, and check for a success property. If it exists and is true, then the api lookup was successful.
The idea is to set the timeout condition then in the worker task, which completely depends on how you're implementing the API lookup. If you're using cURL (or some wrapper around cURL), you can see the answer to how to detect a timeout here.
From the worker side:
$worker= new GearmanWorker();
$worker->addServer();
$worker->addFunction("apiPriceLookup", "apiPriceLookup", $count);
while ($worker->work());
function apiPriceLookup($job) {
$payload = json_decode($job->workload());
try {
$results = [
'data' => PerformApiLookupForProductId($payload->productId),
'success' => true,
];
} catch(Exception $e) {
$results = ['success' => false];
}
return json_encode($results);
}
This just creates a GearmanWorker object and subscribes it the function of apiPriceLookup. It will call the function apiPriceLookup whenever a client submits a task to the job server. That function calls out to another function, PerformApiLookupForProductId, which should be written so as to throw an exception whenever a timeout condition occurs.
I don't think this would be considered using exceptions to control logic flow, I think timeout conditions generally are exceptional (or should be) events. For instance, Guzzle will throw a GuzzleHttp\Exception\RequestException when it has decided to timeout.