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问题:
I have this decorator:
def timed_out(timeout): def decorate(f): if not hasattr(signal, "SIGALRM"): return f def handler(signum, frame): raise TimedOutExc() @functools.wraps(f) def new_f(*args, **kwargs): old = signal.signal(signal.SIGALRM, handler) signal.alarm(timeout) try: result = f(*args, **kwargs) finally: signal.signal(signal.SIGALRM, old) signal.alarm(0) return result new_f.func_name = f.func_name return new_f return decorate
The code only does anything on linux, though, as on windows, there is no SIGALRM. What would be the simplest way to have this code work in Windows as well?
回答1:
It's not very pretty, but I had to do something similar in a cross-platform way, and I came up with using a separate thread. Signal based systems did not work on all platforms reliably.
Use of this class could be wrapped up in a decorator, or made into a with context handler.
YMMV.
#!/usr/bin/env python2.7 import time, threading class Ticker(threading.Thread): """A very simple thread that merely blocks for :attr:`interval` and sets a :class:`threading.Event` when the :attr:`interval` has elapsed. It then waits for the caller to unset this event before looping again. Example use:: t = Ticker(1.0) # make a ticker t.start() # start the ticker in a new thread try: while t.evt.wait(): # hang out til the time has elapsed t.evt.clear() # tell the ticker to loop again print time.time(), "FIRING!" except: t.stop() # tell the thread to stop t.join() # wait til the thread actually dies """ # SIGALRM based timing proved to be unreliable on various python installs, # so we use a simple thread that blocks on sleep and sets a threading.Event # when the timer expires, it does this forever. def __init__(self, interval): super(Ticker, self).__init__() self.interval = interval self.evt = threading.Event() self.evt.clear() self.should_run = threading.Event() self.should_run.set() def stop(self): """Stop the this thread. You probably want to call :meth:`join` immediately afterwards """ self.should_run.clear() def consume(self): was_set = self.evt.is_set() if was_set: self.evt.clear() return was_set def run(self): """The internal main method of this thread. Block for :attr:`interval` seconds before setting :attr:`Ticker.evt` .. warning:: Do not call this directly! Instead call :meth:`start`. """ while self.should_run.is_set(): time.sleep(self.interval) self.evt.set()
回答2:
I find this timeout-decorator code very handy, too. (I originally found it in this question answer: How to limit execution time of a function call in Python)
To make it work on Windows, I use the Python that is installed with Cygwin.
I run setup-x86_64.exe, then select the python3 package from the Python folder. (Or, if you prefer Python 2, the python package.)
To rename python3 to python2, I define the alias
alias python=python3
from the Cygwin command prompt. Since I don't use this functionality very often, I probably won't put it into a .bashrc or anything.
Related question: Python signal don't work even on Cygwin?
