Fatal error does not work locally: newosproc

Question

I have a Flask application with basic files.

server.py:

from flask import Flask app = Flask(__name__) @app.route('/') def hello(): return 'Hello world' if __name__ == '__main__': app.run() 

PROCFILE:

 web: gunicorn server:app --log-file=- 

requirements.txt

 Flask==0.10.1 Jinja2==2.8 MarkupSafe==0.23 Werkzeug==0.10.4 argparse==1.2.1 gunicorn==19.3.0 itsdangerous==0.24 wsgiref==0.1.2 

I installed a hero. The following commands work fine:

 heroku login heroku create source venv/bin/activate pip3 install Flask gunicorn 

When I run heroku local , it gives the following error:

 runtime: failed to create new OS thread (have 6 already; errno=11) fatal error: newosproc 

Sometimes the fatal error: newosproc not displayed.

I even tried reinstalling Heroku and the Heroku toolkit, but that didn't make any difference.

python server.py works just fine!

PS: I am using Ubuntu 14.04.