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Okhttp uses OkHttpClent to send requests.
can I use the same OkHttpClent instance to requests in different Threads ?
Yes. OkHttpClient is thread safe, and the use case you describe is expected. Do not create a new client instance per thread.
But at the same time, consuming a single Response from multiple threads is probably unwise.
See docs here https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/#okhttpclients-should-be-shared
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We started a new project with Quarkus and Mutiny, and created a bunch of endpoints with Quarkus #Funq, everything has been working fine so far. Now we want to process something very time-consuming in one of the endpoints, and what we are expecting is, once user clicks a button to send the http request from frontend and hits this specific endpoint, we are going to return 202 Accepted immediately, leaving the time-consuming operation processing in another thread from backend, then send notification email accordingly to user once it completes.
I understand this can be done with #Async or CompletableFuture, but now we want to do this with Mutiny. Based on how I read Mutiny documentation here https://smallrye.io/smallrye-mutiny/guides/imperative-to-reactive, runSubscriptionOn will avoid blocking the caller thread by running the time-consuming method on another thread, and my testing showed the time-consuming codes did get executed on a different thread. However, the http request does not return immediately, it is still pending until the time-consuming method finishes executing (as I observe in the browser's developer tool). Did I misunderstand how runSubscriptionOn works? How do I implement this feature with Mutiny?
My #Funq endpoint looks like this
#Inject
MyService myService;
#Funq("api/report")
public Uni<String> sendReport(MyRequest request) {
ExecutorService executor = Executors.newFixedThreadPool(10, r -> new Thread(r, "CUSTOM_THREAD"));
return Uni.createFrom()
.item(() -> myService.timeConsumingMethod(request))
.runSubscriptionOn(executor);
}
Edit: I found the solution using Uni based on #Ladicek's answer. After digging deeper into Quarkus and Uni I have a follow-up question:
Currently most of our blocking methods are not returning Uni on Service level, instead we create Uni object from what they return (i.e. object or list), and return the Uni on Controller level in their endpoints like this
return Uni.createFrom().item(() -> myService.myIOBlockingMethod(request)).
As #Ladicek explained, I do not have to use .runSubscriptionOn explicitly as the IO blocking method will automatically run on a worker thread (as my method on Service level does not return Uni). Is there any downside for this? My understanding is, this will lead to longer response time because it has to jump between the I/O thread and worker thread, am I correct?
What is the best practice for this? Should I always return Uni for those blocking methods on Service level so that they can run on the I/O threads as well? If so I guess I will always need to call .runSubscriptionOn to run it on a different worker thread so that the I/O thread is not blocked, correct?
By returning a Uni, you're basically saying that the response is complete when the Uni completes. What you want is to run the action on a thread pool and return a complete response (Uni or not, that doesn't matter).
By the way, you're creating an extra thread pool in the method, for each request, and don't shut it down. That's wrong. You want to create one thread pool for all requests (e.g. in a #PostConstruct method) and ideally also shut it down when the application ends (in a #PreDestroy method).
According to my research, I found out that in thread per request model, every request that comes spawns a new thread. Let's say I had 100 requests, I'd be having 100 threads running at once. Coming to event looped model (similar to spring webflux), we have a main thread that listens to the requests and delegates tasks to other threads.
Now let's say we have 100 requests on event looped model. Here, the main thread will be free to listen but it will also have threads which will be waiting for response from DB or network, just like thread per request model. How does it make event looped model more scalable.
The key difference between Tomcat with Servlet API < 3.1 and servers as Netty powered with a Spring WebFlux is the way which IO and requests are processed : blocking or non-blocking.
Spring WebFlux favors the second approach :
Part of the answer is the need for a non-blocking web stack to handle
concurrency with a small number of threads and scale with fewer
hardware resources.
So to sum that, by using the Spring WebFlux API, much less threads will be created for as many as client http requests because a thread is not dedicated to a single client http request in this model.
The no-blocking approach means that : whatever the time to process a request, a thread that handles that will not block the application and keep the thread waited for a long time but will process another request during this time.
Take that example : your Rest or Mvc controller receives a request and the essential of the task to perform is requesting the database. With a blocking approach you create one thread by http request. With a no blocking approach, the thread delegates to the database, may serve other requests and that thread or another of the pool will go on the processing when the interaction with the database is finished.
I have an array of objects that i need to send to an endpoint. I am currently looping through the array and sending the requests one by one. The issue is that i now have over 35,000 requests to be made, and i need to update the database with the response.In my limited knowledge of springboot , i am not aware of any method i can use to send the 35,000 requests at once (without looping through one by one).
Is the best method to use still employing looping but utilize asynchronous calls, or is there a method that i can use to send the 35,000 http requests at once?..i just need a pointer because i am not aware how threads can be used, since this is already an array and each element needs to be sent.
Thank you
Well, first off 35,000 at a time of, well, anything, is a bad idea.
However, if you look in to the Java ExecutorService, this gives you the ability to fill a queue with tasks, and then each task will be performed by a thread taken from a thread pool. As the threads complete, the service pulls another request from the queue and handles that. So, you simply provide a Runnable that performs your web requests, create an Adequately Sized Thread Pool (which is basically sized through experimentation to give the best throughput), and then let the threads crunch away on the queue of tasks.
You will need a queue large enough to absorb all of your tasks, or you can look at something like the NotifyingBlockingThreadPoolExecutor. This will allow you to just gorge a queue and block when the queue gets to full, until all of your tasks are complete.
Addenda:
I don't know enough about Spring Boot to comment about whether a "batch job" would do what you want or not.
However, on that note, an alternative to creating 35,000 individual entries for the ExecutorService, you could, indeed, send a subset. For example 3,500 entries representing 10 items each, or 350 with 100 each. The idea there is to leverage any potential gains from reusing HTTP connections and what not, so there's less stand up and tear down for each request. Standing up 350 connections if far cheaper than standing up 35,000.
Can I pass the requestBody() headers() or anything else I retrieve from a finished OkHttp Call<> around to other threads, or is it necessary to copy the relevant data first?
You can pass the RequestBody to another thread, but only one thread is allowed to read the body. If multiple threads attempt to read it, you’re going to have a bad time.
Request and response headers are immutable.
(This probably duplicates the question ASP.NET MVC4 Async controller - Why to use?, but about webapi, and I do not agree with answers in there)
Suppose I have a long running SQL request. Its data should be than serialized to JSON and sent to browser (as a response for xhr request). Sample code:
public class DataController : ApiController
{
public Task<Data> Get()
{
return LoadDataAsync(); // Load data asynchronously?
}
}
What actually happens when I do $.getJson('api/data', ...) (see this poster http://www.asp.net/posters/web-api/ASP.NET-Web-API-Poster.pdf):
[IIS] Request is accepted by IIS.
[IIS] IIS waits for one thread [THREAD] from the managed pool (http://msdn.microsoft.com/en-us/library/0ka9477y(v=vs.110).aspx) and starts work in it.
[THREAD] Webapi Creates new DataController object in that thread, and other classes.
[THREAD] Uses task-parallel lib to start a sql-query in [THREAD2]
[THREAD] goes back to managed pool, ready for other processing
[THREAD2] works with sql driver, reads data as it ready and invokes [THREAD3] to reply for xhr request
[THREAD3] sends response.
Please, feel free to correct me, if there's something wrong.
In the question above, they say, the point and profit is, that [THREAD2] is not from The Managed Pool, however MSDN article (link above) says that
By default, parallel library types like Task and Task<TResult> use thread pool threads to run tasks.
So I make a conclusion, that all THREE THREADS are from managed pool.
Furthermore, if I used synchronous method, I would still keep my server responsive, using only one thread (from the precious thread pool).
So, what's the actual point of swapping from 1 thread to 3 threads? Why not just maximize threads in thread pool?
Are there any clearly useful ways of using async controllers?
I think the key misunderstanding is around how async tasks work. I have an async intro on my blog that may help.
In particular, a Task returned by an async method does not run any code. Rather, it is just a convenient way to notify callers of the result of that method. The MSDN docs you quoted only apply to tasks that actually run code, e.g., Task.Run.
BTW, the poster you referenced has nothing to do with threads. Here's what happens in an async database request (slightly simplified):
Request is accepted by IIS and passed to ASP.NET.
ASP.NET takes one of its thread pool threads and assigns it to that request.
WebApi creates DataController etc.
The controller action starts an asynchronous SQL query.
The request thread returns to the thread pool. There are now no threads processing the request.
When the result arrives from the SQL server, a thread pool thread reads the response.
That thread pool thread notifies the request that it is ready to continue processing.
Since ASP.NET knows that no other threads are handling that request, it just assigns that same thread the request so it can finish it off directly.
If you want some proof-of-concept code, I have an old Gist that artificially restricts the ASP.NET thread pool to the number of cores (which is its minimum setting) and then does N+1 synchronous and asynchronous requests. That code just does a delay for a second instead of contacting a SQL server, but the general principle is the same.
The profit of asynchronous actions is that while the controller is waiting for the sql query to finish no threads are allocated for this request, while if you used a synchronous method a thread would be locked up in the execution of this method from the start to end of that method. While SQL server is doing its job the thread isn't doing anything but waiting.
If you use asynchronous methods this same thread can respond to other requests while SQL server is doing its thing.
I believe your steps are wrong at step 4, I don't think it will create a new thread to do the SQL query. At 6 there isn't created a new thread, it is just one of the available threads that will be used to continue from where the first thread left off. The thread at 6 could be the same as started the async operation.
The point of async is not to make an application multi threaded but rather to let a single threaded application carry on with something different instead of waiting for a response from an external call that is executing on a different thread or process.
Consider a desk top application that shows stock prices from different exchanges. The application needs to make a couple of REST / http calls to get some data from each of the remote stock exchange servers.
A single threaded application would make the first call, wait doing nothing until it got the first set of prices, update it's window, then make a call to the next external stock price server, again wait doing nothing until it got the prices, update it's window... etc..
We could go all multi threaded kick off the requests in parallel and update the screen in parallel, but since most of the time is spent waiting for a response from the remote server this seems overkill.
It might be better for the thread to:
Make a request for the first server but instead of waiting for the answer leave a marker, a place to come back to when the prices arrive and move on to issuing the second request, again leaving a marker of a place to come back to...etc.
When all the requests have been issued the application execution thread can go on to dealing with user input or what ever is required.
Now when a response from one of the servers is received the thread can be directed to continue from the marker it laid down previously and update the window.
All of the above could have been coded long hand, single threaded, but was so horrendous going multi threaded was often easier. Now the process of leaving the marker and coming back is done by the compiler when we write async/await. All single threaded.
There are two key points here:
1) Multi threaded does still happen! The processing of our request for stock prices happens on a different thread (on a different machine). If we were doing db access the same would be true. In examples where the wait is for a timer, the timer runs on a different thread. Our application though is single threaded, the execution point just jumps around (in a controlled manner) while external threads execute
2) We lose the benefit of async execution as soon as the application requires an async operation to complete. Consider an application showing the price of coffee from two exchanges, the application could initiate the requests and update it's windows asynchronously on a single thread, but now if the application also calculated the difference in price between two exchanges it would have to wait for the async calls to complete. This is forced on us because an async method (such as one we might write to call an exchange for a stock price) does not return the stock price but a Task, which can be thought of as a way to get back to the marker that was laid down so the function can complete and return the stock price.
This means that every function that calls an async function needs to be async or to wait for the "other thread/process/machine" call at the bottom of the call stack to complete, and if we are waiting for the bottom call to complete well why bother with async at all?
When writing a web api, IIS or other host is the desktop application, we write our controller methods async so that the host can execute other methods on our thread to service other requests while our code is waiting for a response from work on a different thread/process/machine.
I my opinion the following describes a clear advantage of async controllers over synchronous ones.
A web application using synchronous methods to service high latency
calls where the thread pool grows to the .NET 4.5 default maximum of
5, 000 threads would consume approximately 5 GB more memory than an
application able the service the same requests using asynchronous
methods and only 50 threads. When you’re doing asynchronous work,
you’re not always using a thread. For example, when you make an
asynchronous web service request, ASP.NET will not be using any
threads between the async method call and the await. Using the thread
pool to service requests with high latency can lead to a large memory
footprint and poor utilization of the server hardware.
from Using Asynchronous Methods in ASP.NET MVC 4