CODEWITHSUNDEEP
flaskcelerybackground-task
Yaniv
Yaniv

Reputation: 79

Flask can handle several background tasks without using Celery

As I understand, using Flask without Celery will block the server availability when a user starts a long operation.

My web server is actually not exposed to the internet and the maximum amount of users that will be connected at a time will be 3 (its of internal use for invoking automation scripts).

I have created a test environment in order to check how Flask is handling several calls at a time.

I have created 'task1' and 'task2' and run a loop with print statement + sleep in order to block the main thread for several seconds.

It seems like its not really blocking the main thead!!! I can run 'task1' start to see the output for every loop and then run 'task2' and see the output of 'task2' together with task one.

I checked the limit and it seems like I can run 7 tasks without blocking. How is that possible? according to the above, I dont need to use Celery in my organization since I will have no scenario that 2 users will run more then 2 tasks at a time.

Can someone explain why 'task1' is not blocking the starting of 'task2'?

@app.route('/task1', methods=['POST'])
def task1():
    for i in range(4):
        print('task 1 - ' + str(i))
        time.sleep(1)
    return 'message'

@app.route('/task2', methods=['POST'])
def task2():
    for i in range(5):
        print('task 2 - ' + str(i))
        time.sleep(1)
    return 'message'

    <script >
        function runTask(){
            document.getElementById('task').value = "this is a value"
    let req = $.ajax({
        url : '/task1',
        type : 'POST', // post request
        data : { }
    });

    req.done(function (data) {
    });
            }

        function runLongerTask(){
            document.getElementById('longer_task').value = "this is longer value"
            let req = $.ajax({
        url : '/task2',
        type : 'POST', // post request
        data : { }
    });

    req.done(function (data) {
    });
}

    </script>

I expected 'task1' to start only when 'task2' will finish but it seems like the two tasks is running in threads (without actually configuring a thread) Here is the results that I got:

task 2 - 0

task 1 - 0

task 2 - 1

task 1 - 1

task 2 - 2

task 1 - 2

task 2 - 3

task 1 - 3

task 2 - 4

Upvotes: 0

Views: 1648

Answers (1)

Nino Walker
Nino Walker

Reputation: 2903

As I understand, using Flask without Celery will block the server availability when a user starts a long operation.

This is not precisely correct, although it's a good rule of thumb to keep heavy workloads out of your webserver for lots of reasons.

You haven't described how you are running flask - with a WSGI container, or the run options. I'd look there to understand how concurrency is configured.

Upvotes: 0

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