Timeout(): a real world example

Writing Functions in Python

Shayne Miel

Software Architect @ Duo Security

Timeout


def function1():
  # This function sometimes
  # runs for a loooong time
  ...


def function2():
  # This function sometimes
  # hangs and doesn't return
  ...

Timeout

@timeout
def function1():
  # This function sometimes
  # runs for a loooong time
  ...

@timeout
def function2():
  # This function sometimes
  # hangs and doesn't return
  ...

stopwatch

Timeout - background info

import signal

def raise_timeout(*args, **kwargs):
  raise TimeoutError()

# When an "alarm" signal goes off, call raise_timeout()
signal.signal(signalnum=signal.SIGALRM, handler=raise_timeout)

# Set off an alarm in 5 seconds
signal.alarm(5)

# Cancel the alarm
signal.alarm(0)

def timeout_in_5s(func):

  @wraps(func)
  def wrapper(*args, **kwargs):

    # Set an alarm for 5 seconds
    signal.alarm(5)

    try:
      # Call the decorated func
      return func(*args, **kwargs)

    finally:
      # Cancel alarm
      signal.alarm(0)

  return wrapper

@timeout_in_5s
def foo():
  time.sleep(10)
  print('foo!')

foo()

TimeoutError

def timeout(n_seconds):

  def decorator(func):

    @wraps(func)
    def wrapper(*args, **kwargs):

      # Set an alarm for n seconds
      signal.alarm(n_seconds)

      try:
        # Call the decorated func
        return func(*args, **kwargs)
      finally:
        # Cancel alarm
        signal.alarm(0)

    return wrapper

  return decorator

@timeout(5)
def foo():
  time.sleep(10)
  print('foo!')

@timeout(20)
def bar():
  time.sleep(10)
  print('bar!')

foo()

TimeoutError

bar()

bar!

Let's practice!

Writing Functions in Python