Develop Reference

Handle Multiple Concurent Requests for Express Sever on Same Endpoint API

this question might be duplicated but I am still not getting the answer. I am fairly new to node.js so I might need some help. Many have said that node.js is perfectly free to run incoming requests asynchronously, but the code below shows that if multiple requests hit the same endpoint, say /test3, the callback function will:
Print "test3"
Call setTimeout() to prevent blocking of event loop
Wait for 5 seconds and send a response of "test3" to the client
My question here is if client 1 and client 2 call /test3 endpoint at the same time, and the assumption here is that client 1 hits the endpoint first, client 2 has to wait for client 1 to finish first before entering the event loop.
Can anybody here tells me if it is possible for multiple clients to call a single endpoint and run concurrently, not sequentially, but something like 1 thread per connection kind of analogy.
Of course, if I were to call other endpoint /test1 or /test2 while the code is still executing on /test3, I would still get a response straight from /test2, which is "test2" immediately.
app.get("/test1", (req, res) => {
console.log("test1");
setTimeout(() => res.send("test1"), 5000);
});
app.get("/test2", async (req, res, next) => {
console.log("test2");
res.send("test2");
});
app.get("/test3", (req, res) => {
console.log("test3");
setTimeout(() => res.send("test3"), 5000);
});

For those who have visited, it has got nothing to do with blocking of event loop.
I have found something interesting. The answer to the question can be found here.
When I was using chrome, the requests keep getting blocked after the first request. However, with safari, I was able to hit the endpoint concurrently. For more details look at the following link below.
GET requests from Chrome browser are blocking the API to receive further requests in NODEJS

Run your application in cluster. Lookup Pm2

This question needs more details to be answer and is clearly an opinion-based question. just because it is an strawman argument I will answer it.
first of all we need to define run concurrently, it is ambiguous if we assume the literal meaning in stric theory nothing RUNS CONCURRENTLY
CPUs can only carry out one instruction at a time.
The speed at which the CPU can carry out instructions is called the clock speed. This is controlled by a clock. With every tick of the clock, the CPU fetches and executes one instruction. The clock speed is measured in cycles per second, and 1c/s is known as 1 hertz. This means that a CPU with a clock speed of 2 gigahertz (GHz) can carry out two thousand million (or two billion for those in the US) for the rest of us/world 2000 million cycles per second.
cpu running multiple task "concurrently"
yes you're right now-days computers even cell phones comes with multi core which means the number of tasks running at the same time will depend upon the number of cores, but If you ask any expert such as this Associate Staff Engineer AKA me will tell you that is very very rarely you'll find a server with more than one core. why would you spend 500 USD for a multi core server if you can spawn a hold bunch of ...nano or whatever option available in the free trial... with kubernetes.
Another thing. why would you handle/configurate node to be incharge of the routing let apache and/or nginx to worry about that.
as you mentioned there is one thing call event loop which is a fancy way of naming a Queue Data Structure FIFO
so in other words. no, NO nodejs as well as any other programming language out there will run
but definitly it depends on your infrastructure.

NodeJS Returning data to client browser

I think we need some help here. Thanks in advance.
I have been doing programming in .Net for desktop applications and have used Timer objects to wait for a task to complete before the task result are shown in a data grid. Recently, we switched over to NodeJs and find it pretty interesting. We could design a small application that executes some tasks using PowerShell scripts and return the data to the client browser. However, I would have to execute a Timer on the client browser (when someone clicks on a button) to see if the file, that Timer receives from the server, has "ENDOFDATA" or not. Once the Timer sees ENDOFDATA it triggers another function to populate DIV with the data that was received from the server.
Is this the right way to get the data from a server? We really don't want to block EventLoop. We run PowerShell scripts on NodeJS to collect users from Active Directory and then send the data back to the client browser. The PowerShell scripts are executed as a Job so EventLoop is not blocked.
Here is an example of the code at NodeJs:
In the below code can we insert something that won't block the EventLoop but still respond to the server once the task is completed? As you can see in the code below, we would like to send the ADUsers.CSV file to the client browser once GetUsers.PS1 has finished executing. Since GetUSers.PS1 takes about five minutes to complete the Event Loop is blocked and the Server can no longer accept any other requests.
app.post("/LoadDomUsers", (request, response) => {
//we check if the request is an AJAX one and if accepts JSON
if (request.xhr || request.accepts("json, html") === "json") {
var ThisAD = request.body.ThisAD
console.log(ThisAD);
ps.addCommand("./public/ps/GetUsers.PS1", [{
name: 'AllParaNow',
value: ScriptPara
}])
ps.addCommand(`$rc = gc ` + __dirname + "/public/TestData/AD/ADUsers.CSV");
ps.addCommand(`$rc`);
ps.invoke().then((output) => {
response.send({ message: output });
console.log(output);
});
}
});
Thank you.

The way you describe your problem isn't that clear. I had to read some of the comments in your initial question just to be sure I understood the issue. Honestly, you could just utilize various CSV NPM packages to read and write from your active directory with NodeJS.
I/O is non-blocking with NodeJS, so you're not actually blocking the EventLoop. You can handle multiple I/O requests, since NodeJS will just create threads for each one,
and continue execution on the main thread until the I/O operations complete and send back the data to its function reference, adding them as functions to the callstack and resuming program execution from those function's references. After you get the I/O data, you just send it back to the client through the response object. There should be no timers needed.
So is the issue once the powershell script runs, you have to wait for that initial script to complete before being able to handle pending requests? I'm still a bit unclear...

Running tasks in parallel with reliability in cloud functions

I'm streaming and processing tweets in Firebase Cloud Functions using the Twitter API.
In my stream, I am tracking various keywords and users of Twitter, hence the influx of tweets is very high and a new tweet is delivered even before I have processed the previous tweet, which leads to lapses as the new tweet sometimes does not get processed.
This is how my stream looks:
...
const stream = twitter.stream('statuses/filter', {track: [various, keywords, ..., ...], follow: [userId1, userId2, userId3, userId3, ..., ...]});
stream.on('tweet', (tweet) => {
processTweet(tweet); //This takes time because there are multiple network requests involved and also sometimes recursively running functions depending on the tweets properties.
})
...
processTweet(tweet) essentially is compiling threads from twitter, which takes time depending upon the length of the thread. Sometimes a few seconds also. I have optimised processTweet(tweet) as much as possible to compile the threads reliably.
I want to run processTweet(tweet) parallelly and queue the tweets that are coming in at the time of processing so that it runs reliably as the twitter docs specify.
Ensure that your client is reading the stream fast enough. Typically you should not do any real processing work as you read the stream. Read the stream and hand the activity to another thread/process/data store to do your processing asynchronously.
Help would be very much appreciated.

This twitter streaming API will not work with Cloud Functions.
Cloud Functions code can only be invoked in response to incoming events, and the code may only run for up to 9 minutes max (default 60 seconds). After that, the function code is forced to shut down. With Cloud Functions, there is no way to continually process some stream of data coming from an API.
In order to use this API, you will need to use some other compute product that allows you to run code indefinitely on a dedicated server instance, such as App Engine or Compute Engine.

How to make express Node.JS reply a request during heavy workload?

I'm creating an nodejs web processor. I's is processing time that takes ~ 1 minute. I POST to my server and get status by using GET
this is my simplified code
// Configure Express
const app = express();
app.listen(8080);
// Console
app.post('/clean, async function(req, res, next) {
// start proccess
let result = await worker.process(data);
// Send result when finish
res.send(result);
});
// reply with when asked
app.get('/clean, async function(req, res, next) {
res.send(worker.status);
});
The problem is. The server is working so hard in the POST /clean process that GET /clean are not replied in time.
All GET /clean requests are replied after the worker finishes its task and free the processor to respond the request.
In other words. The application are unable to respond during workload.
How can I get around this situation?

Because node.js runs your Javascript as single threaded (only one piece of Javascript ever running at once) and does not time slice, as long as your worker.process() is running it's synchronous code, no other requests can be processed by your server. This is why worker.process() has to finish before any of the http requests that arrived while it was running get serviced. The node.js event loop is busy until worker.process() is done so it can't service any other events (like incoming http requests).
These are some of the ways to work around that:
Cluster your app with the built-in cluster module so that you have a bunch of processes that can either work on worker.process() code or handle incoming http requests.
When it's time to call worker.process(), fire up a new node.js process, run the processing there and communicate back the result with standard interprocess communication. Then, your main node.js process stays reading to handle incoming http requests near instantly as they arrive.
Create a work queue of a group of additional node.js processes that run jobs that are put in the queue and configure these processes to be able to run your worker.process() code from the queue. This is a variation of #2 that bounds the number of processes and serializes the work into a queue (better controlled than #2).
Rework the way worker.process() does its work so that it can do a few ms of work at a time, then return back to the message loop so other events can run (like incoming http requests) and then resume it's work afterwards for a few more ms at a time. This usually requires building some sort of stateful object that can do a little bit of work at a time each time it is called, but is often a pain to program effectively.
Note that #1, #2 and #3 all require that the work be done in other processes. That means that the process.status() will need to get the status from those other processes. So, you will either need some sort of interprocess way of communicating with the other processes or you will need to store the status as you go in some storage that is accessible from all processes (such as redis) so it can just be retrieved from there.

There's no working around the single-threaded nature of JS short of converting your service to a cluster of processes or to use something experimental like Worker Threads.
If neither of these options work for you, you'll need to yield up the processing thread periodically to give other tasks the ability to work on things:
function workPart1() {
// Do a bunch of stuff
setTimeout(workPart2, 10);
}
function workPart2() {
// More stuff
setTimeout(workPart3, 10); // etc.
}

understanding of node js performance

I recently discovered Node js and I read in various articles that Node js is fast and can handle more requests than a Java server although Node js use a single thread.
I understood that Node is based on an event loop, each call to a remote api or a database is done with an async call so the main thread is never blocked and the server can continue to handle others client requests.
If I understood well, each portion of code that can take times should be processed with an async call otherwise the server will be blocked and it won't be able to handle others requests ?
var server = http.createServer(function (request, response) {
//CALL A METHOD WHICH CAN TAKE LONG TIME TO EXECUTE
slowSyncMethod();
//THE SERVER WILL STILL BE ABLE TO HANDLER OTHERS REQUESTS ??
response.writeHead(200, {"Content-Type":"text/plain"});
response.end("");
});
So if my understanding is correct, the above code is bad because the synchronous call to the slow method will block the Node js main thread ? Is Node js fast on condition that all the code that can take times are executed in an async manner ?

NodeJs is as fast as your hardware(vm) and the v8 that is running it. that being said, any heavy duty task like any type of media(music, image, video etc) file processing will definitively lock your application. so will computation on large collections thats why the async model is leveraged though events, and deferred invocations. that being said nothing stops you from spawning child processes to relegate heavy duty and asynchronously get back the result. But if you are finding your self in the need to do this for many tasks, maybe you should revisit your architecture.
I hope thhis helps