example.py

import time
from uuid import uuid4

from twisted.internet import threads
from crochet import run_in_reactor, setup
setup()

import structlog
logger = structlog.get_logger()

from flask import Flask, session, g, request


app = Flask(__name__)

structlog.configure(
    processors=[
        structlog.processors.KeyValueRenderer(
            key_order=['reqid', 'event'],
        ),
    ],
    context_class=structlog.threadlocal.wrap_dict(dict),
)

def run_async(func, *args, **kwargs):
    """
    Run a function in another thread.
    """
    @run_in_reactor
    def run_func():
        # XXX Set up the logger so that you can tie what
        # happens inside this function back to the request
        # that started it.
        d = threads.deferToThread(func, *args, **kwargs)
        def eb(err):
            logger.exception('error processing async func', exc_info=err)
            return
        d.addErrback(eb)
    run_func()


@app.before_request
def before_request():
    log = logger.new(reqid=str(uuid4()))
    log.bind(path=request.path)
    g.user_id = session.get('user_id', None)
    if g.user_id:
        log.bind(user_id=g.user_id)

def send_an_email(email):
    # pretend to send an email
    logger.info('preparing to send an email', email=email)
    time.sleep(2)
    logger.info('email sent', email=email)

@app.route('/')
def root():
    logger.info('request started')
    run_async(send_an_email, 'foo@foo.com')
    return 'I sent an email'

app.run('127.0.0.1', 5000)