Celery/Flask/Redis - apply_async function doesn't work - Updated 2 - flask

Question

everyone.
app.config['CELERY_BROKER_URL'] = 'redis://localhost:6379/0'
app.config['CELERY_RESULT_BACKEND'] = 'redis://localhost:6379/0'
celery = Celery(app.name, broker=app.config['CELERY_BROKER_URL'])
celery.conf.update(app.config)
def upload():
if checkDouble == None:
do_async_upload.apply_async(args=[checkDouble], countdown=15)
return 'Saved ' + file.filename
else:
return "File exists"
#celery.task
def do_async_upload(pic):
print("hello2")
db.session.add(pic)
db.session.commit()
return 0
But do_sync_upload doesn't work (hello2 doesn't print), it just skips. Redis server is working correctly
Updated:
if checkDouble == None:
print('Hello')
async_result = do_async_upload.delay(checkDouble)
print(async_result)
result = async_result.get()
return 'Saved ' + file.filename
else:
return "File exists"
But do_async_upload.apply_async doesn't seem to execute at all.
Maybe there is a problem in my Redis? Server is working, but after I try to submit something it turns from 0 to 4 clients connected.
Or even I have a problem with my datetime settings.
UPDATE 2:
I tried 2 different examples with Flask and Celery and none of them work. Redis server shows some activity, but no.
Both of them are using the same function:
Code from https://github.com/ro6ley/flask-celery-demo:
#client.task
def send_mail(data):
with app.app_context():
msg = Message("Ping!",
sender="admin.ping",
recipients=[data['email']])
msg.body = data['message']
mail.send(msg)
#app.route('/', methods=['GET', 'POST'])
def index():
if request.method == 'GET':
return render_template('index.html')
elif request.method == 'POST':
data = {}
data['email'] = request.form['email']
data['first_name'] = request.form['first_name']
data['last_name'] = request.form['last_name']
data['message'] = request.form['message']
duration = int(request.form['duration'])
duration_unit = request.form['duration_unit']
print("1")
send_mail.apply_async(args=[data], countdown=duration)
print("2")
flash(f"Email will be sent to {data['email']} in {request.form['duration']} {duration_unit}")
It shows flash message, but message isn't coming. Config.py is set correctly.
Next application:
#app.route('/', methods=['GET', 'POST'])
def index():
if request.method == 'GET':
return render_template('index.html', email=session.get('email', ''))
email = request.form['email']
session['email'] = email
# send the email
email_data = {
'subject': 'Hello from Flask',
'to': email,
'body': 'This is a test email sent from a background Celery task.'
}
if request.form['submit'] == 'Send':
# send right away
send_async_email.delay(email_data)
flash('Sending email to {0}'.format(email))
else:
# send in one minute
send_async_email.apply_async(args=[email_data], countdown=60)
flash('An email will be sent to {0} in one minute'.format(email))
return redirect(url_for('index'))
#celery.task
def send_async_email(email_data):
"""Background task to send an email with Flask-Mail."""
msg = Message(email_data['subject'],
sender=app.config['MAIL_DEFAULT_SENDER'],
recipients=[email_data['to']])
msg.body = email_data['body']
with app.app_context():
mail.send(msg)
None of the options work.

Answer 1

apply_async() returns an AsyncResult object IMMEDIATELY so no wonder you do not see anything and think do_async_upload() did not execute...
So here are two things I suggest you do:
1) Modify the upload() to have something like:
async_result = do_async_upload.apply_async(args=[checkDouble], countdown=15)
# .get() blocks until the task is done and returns
result = async_result.get()
2) Do not call print() in Celery tasks. Use the get_task_logger() function to obtain Celery's logger object and use it in your tasks. There is a whole section in the documentation about it.