我想在Python中每60秒重复执行一个函数(就像Objective C中的NSTimer或JS中的setTimeout)。这段代码将作为守护进程运行,有效地类似于使用cron每分钟调用python脚本,但不需要用户设置。
在这个关于用Python实现的cron的问题中,解决方案似乎只有效地使()休眠x秒。我不需要这么高级的功能,所以也许这样的东西可以工作
while True:
# Code executed here
time.sleep(60)
这段代码是否存在任何可预见的问题?
以下是MestreLion代码的改编版本。
除了原来的函数,这段代码:
1)添加用于在特定时间触发计时器的first_interval(调用者需要计算first_interval并传递进来)
2)在原代码中解决一个竞态条件。在原始代码中,如果控制线程未能取消正在运行的计时器(“停止计时器,并取消计时器动作的执行。这只会在计时器仍处于等待阶段时起作用。”引用自https://docs.python.org/2/library/threading.html),计时器将无休止地运行。
class RepeatedTimer(object):
def __init__(self, first_interval, interval, func, *args, **kwargs):
self.timer = None
self.first_interval = first_interval
self.interval = interval
self.func = func
self.args = args
self.kwargs = kwargs
self.running = False
self.is_started = False
def first_start(self):
try:
# no race-condition here because only control thread will call this method
# if already started will not start again
if not self.is_started:
self.is_started = True
self.timer = Timer(self.first_interval, self.run)
self.running = True
self.timer.start()
except Exception as e:
log_print(syslog.LOG_ERR, "timer first_start failed %s %s"%(e.message, traceback.format_exc()))
raise
def run(self):
# if not stopped start again
if self.running:
self.timer = Timer(self.interval, self.run)
self.timer.start()
self.func(*self.args, **self.kwargs)
def stop(self):
# cancel current timer in case failed it's still OK
# if already stopped doesn't matter to stop again
if self.timer:
self.timer.cancel()
self.running = False
下面是MestreLion对代码的更新,它可以避免随着时间的推移而漂移。
这里的RepeatedTimer类按照OP的请求每隔“间隔”秒调用给定函数;调度并不取决于函数执行的时间。我喜欢这个解决方案,因为它没有外部库依赖关系;这是纯python。
import threading
import time
class RepeatedTimer(object):
def __init__(self, interval, function, *args, **kwargs):
self._timer = None
self.interval = interval
self.function = function
self.args = args
self.kwargs = kwargs
self.is_running = False
self.next_call = time.time()
self.start()
def _run(self):
self.is_running = False
self.start()
self.function(*self.args, **self.kwargs)
def start(self):
if not self.is_running:
self.next_call += self.interval
self._timer = threading.Timer(self.next_call - time.time(), self._run)
self._timer.start()
self.is_running = True
def stop(self):
self._timer.cancel()
self.is_running = False
示例用法(摘自MestreLion的回答):
from time import sleep
def hello(name):
print "Hello %s!" % name
print "starting..."
rt = RepeatedTimer(1, hello, "World") # it auto-starts, no need of rt.start()
try:
sleep(5) # your long-running job goes here...
finally:
rt.stop() # better in a try/finally block to make sure the program ends!