Pycopine - Handle with Care

Pycopine is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.

As this copy-pasted text suggests, pycopine is heavily inspired by Hystrix <https://github.com/Netflix/Hystrix>_.

Prerequisites

Pycopine requires Python 3.2+, but may be backportet to 2.7 in the future.

(Planned) Features

• Detect and report failing services.
• Short-circuit services that fail on high load to help them recover.
• Monitor failure rates and performance metrics to detect bottlenecks.
• Manage thread pool and queue sizes on demand, at runtime, from everywhere.
• ... (more to come)

Example

Lets say we want to speak to a remote service that is slow, unreliable or both:

.. code-block:: python

import time
import random

def crappy_service(value):
    ''' The most useless piece of code ever.'''
    time.sleep(5)
    if 'OK' != random.choice(['OK', 'OK', 'SERVER ON FIRE']):
        raise RuntimeError('We broke something :(')
    return value

You could throw lots of threads and try/except clauses at the problem and hope to not break the internet. Or you could use pycopine:

.. code-block:: python

from pycopine import Command

class MyCommand(Command):
    ''' Does nothing with the input, but with style. '''

    def run(self, value):
        return crappy_service(value)

    def fallback(self, value):
        return 'some fallback value'

# Run and wait for the result
result = MyCommand('input').result()

# Give up after 2 seconds
result = MyCommand('input').result(timeout=2)

# Fire and forget
MyCommand('input').submit()

# Do stuff in parallel
foo = MyCommand('input').submit()
bar = MyCommand('input').submit()
results = [foo.result(), bar.result()]

# Change your mind midway through
foobar = MyCommand('input').submit()
if foobar.wait(timeout=2):
    result = foobar.result()
else:
    foobar.cancel(RuntimeError('We have no time for this!'))