How do I write a timeout decorator that can receive a function or a decorated function?
I have the following timeout creation decorator function:
class TimeoutError(Exception): pass
def timeout(seconds, error_message = 'Function call timed out'):
def decorated(func):
print "timeout: \t" + func.__name__
def _handle_timeout(signum, frame):
raise TimeoutError(error_message)
def wrapper(*args, **kwargs):
signal.signal(signal.SIGALRM, _handle_timeout)
signal.alarm(seconds)
try:
print "timeout wrapper: \t" + func.__name__
result = func(*args, **kwargs)
finally:
signal.alarm(0)
return result
return functools.wraps(func)(wrapper)
return decorated
And one more decorator:
import inspect
class withHostAndToken(object):
__name__ = "withHostAndToken"
__doc__ = "Get the Host and Token for the API call"
def __init__(self, func):
print "withHostAndToken: \t" + func.__name__
self.func = func
self.HOST = ''
self.TOKEN = ''
def __call__(self,*args, **kwds):
if self.HOST == '':
self.HOST = "HOST"
if self.TOKEN == '':
self.TOKEN = "TOKEN"
argsspec = inspect.getargspec(self.func)
function_args = argsspec[0]
if 'HOST' in function_args:
if 'TOKEN' in function_args:
return self.func(self.HOST , self.TOKEN , *args, **kwds)
else:
return self.func(self.HOST , *args, **kwds)
elif 'TOKEN' in function_args:
return self.func(self.TOKEN, *args, **kwds)
When I try to apply both to a function, I don't get the function code:
@timeout(2)
@withHostAndToken
def testDecorators():
print __name__
while True:
print '.'
testDecorators()
output of this:
withHostAndToken: testDecorators
timeout: withHostAndToken
timeout: withHostAndTokenProcess ended with exit code 0
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Your problem is not there and the decorator chaining works fine.
Here's some sample code to demonstrate it with your decorators:
>>> @timeout(2)
@withHostAndToken
def bar(*args):
print(*args)
i = 0;
while True:
dummy = sys.stderr.write('.')
>>> bar('foo')
host token foo
....................................................................................................................................................................................................................................................................................................................................................................................................................Traceback (most recent call last):
File "<pyshell#48>", line 1, in <module>
bar('foo')
File "<pyshell#2>", line 10, in wrapper
result = func(*args, **kwargs)
File "<pyshell#5>", line 19, in __call__
return self.func(self.HOST , self.TOKEN , *args, **kwds)
File "<pyshell#47>", line 7, in bar
dummy = sys.stderr.write('.')
... message list truncate for brievety ...
File "<pyshell#2>", line 4, in _handle_timeout
raise TimeoutError(error_message)
TimeoutError: Function call timed out
>>>
Thus, the function is correctly intercepted after about 2 seconds as expected.
But in your use case, you used time.sleep
inside the innermost function. And in Linux and other Unixes, it sleep
is implemented via ... SIGALRM
!
So here's what's going on:
- outside decorators ask the alarm to go up after 10 seconds. Interior decorator
- passes an additional parameter to the function
- the function is called and calls
sleep(20)
- calling the function
sleep
resets the alarm timeout to 20 seconds!
- calling the function
This is the reason why the function actually lasts 20 seconds instead of 10 ...
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