Parallel HTTP requests with Retrofit

Question

I have an Android application that is currently using Volley library to make network requests and show downloaded images with NetworkImageView.

I would like to test Retrofit's capabilities and since I need to run lots of requests (thousands) I'm a bit concerned about the parallel execution. Volley handles parallel requests with the RequestQueue that limits the concurrent running requests to four, while the other requests are enqueued waiting to be executed. In Retrofit documentations I haven't found any way to handle the number of concurrent requests and I suspect that such details are left to the developer in this library.

Is this correct? If so, is there any android-oriented implementation/library available? Otherwise, what are the best practices to handle parallel requests?

Solution

Retrofit uses an Executor for queueing requests.

The default uses Executors.newCachedThreadPool which allows for unlimited threads. This fits most use cases since normally you would only ever have one or two requests happening at once.

You can change this behavior, however, by supplying your own when building the RestAdapter. Call setExecutors and pass in an executor that uses a confined thread pool (limited to whatever number you would like). For the second argument, simply pass a new instance of MainThreadExecutor so that callbacks happen on the main thread.

Comments

[Vektor88]

Are you suggesting to use a ThreadPoolExecutor to handle my threads? If yes, I was using this before migrating to Volley, but I had two main problems: 1) I was losing some requests because the queue was full, Volley has an unbounded queue. 2) Some requests were removed from the queue because they were waiting too long.

[Jake Wharton]

Yes. Using an unbounded queue will solve both 1 and 2. There are a few in java.util.concurrent to choose from.

[Jake Wharton]

Awesome! Glad it was helpful.

[Kaloyan Roussev]

Please provide code example of how to limit to max 5 requests at a time

[Matthew Daumen]

RestAdapter restAdapter = new RestAdapter.Builder() .setEndpoint(SomeEndpoint) .setExecutors(Executors.newFixedThreadPool(5), null) .build(); Note the second arg is the callback executor - this will put the callback on the same thread as the client. square.github.io/retrofit/javadoc/retrofit/…

[remedy.]

@JakeWharton So when building the RestAdapter and using setExecutors, it will set a specified number of allowed requests to be put into the queue (if needed) correct? How would one be able to handle the concurrency upon receiving the response from the CallBack? Does retrofit handle this?

[Riten]

Can this method be used with the latest Retrofit 2.0 ??

[pba]

With retrofit 2.0, as in written in this retrofit github issue, OkHttpClient dispatcher has to be used. There is a sample in this other github issue.