A simple Flask wrapper for concurrent.futures
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README.md

Flask-Executor

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Sometimes you need a simple task queue without the overhead of separate worker processes or powerful-but-complex libraries beyond your requirements. Flask-Executor is an easy to use wrapper for the concurrent.futures module that lets you initialise and configure executors via common Flask application patterns. It's a great way to get up and running fast with a lightweight in-process task queue.

Setup

Flask-Executor is available on PyPI and can be installed with:

pip install flask-executor

The Executor extension can either be initialized directly:

from flask import Flask
from flask_executor import Executor

app = Flask(__name__)

executor = Executor(app)

Or through the factory method:

executor = Executor()

executor.init_app(app)

Configuration

app.config['EXECUTOR_TYPE']

Specify which kind of executor to initialise. Valid values are 'thread' (default) to initialise a concurrent.futures.ThreadPoolExecutor, or 'process' to initialise a concurrent.futures.ProcessPoolExecutor.

app.config['EXECUTOR_MAX_WORKERS']

Define the number of worker threads for a ThreadPoolExecutor or the number of worker processes for a ProcessPoolExecutor. Valid values are any integer or None (default) to let the concurrent.futures module pick defaults for you.

Usage

You can submit examples to the executor just as you would expect:

from flask import Flask
from flask_executor import Executor

app = Flask(__name__)
executor = Executor(app)

def fib(n):
    if n <= 2:
        return 1
    else:
        return fib(n-1) + fib(n-2)

@app.route('/example1')
def example1():
    executor.submit(fib, 5)
    return 'OK'

Jobs submitted to the executor are wrapped with the current app and executed inside the app context so that tasks requiring an app context can run outside your main thread or process without requiring you to modify the function to handle this yourself.

Submitting examples to the executor returns standard concurrent.futures.Future objects that you can work with:

import concurrent.futures
from flask import Response

@app.route('/example2')
def example2():
    future = executor.submit(fib, 5)
    return str(future.result())

@app.route('/example3')
def example3():
    futures = [executor.submit(fib, i) for i in range(1, 40)]
    def generate():
        for future in concurrent.futures.as_completed(futures):
            yield str(future.result()) + '\n'
    return Response(generate(), mimetype='text/text')

If you're using a ThreadPoolExecutor, you can use a decorator pattern in the style of Celery or Dramatiq to decorate functions which can then be submitted to the executor directly:

@executor.job
def fib(n):
    if n <= 2:
        return 1
    else:
        return fib(n-1) + fib(n-2)

@app.route('/example4')
def example4():
    fib.submit(5)
    return 'OK'

ThreadPoolExecutor jobs are also wrapped with a copy of the current app object and executed inside its app context, so that tasks requiring an app context can run outside your main thread.

Note: decoration is not currently supported when using a ProcessPoolExecutor, due to the multiprocessing library's inability to work with decorated functions.