在这里检查循环中的时间可能没有必要,而且很浪费,因为您可以将线程置于睡眠状态,并在时间到时让内核将其唤醒。
线程库提供threading.Timer https://docs.python.org/3/library/threading.html#timer-objects对于此类用例。您的情况的困难在于,您无法中断这样的睡眠线程来调整执行指定函数的时间间隔。
我正在使用自定义管理器类TimeLord
在我下面的例子中,为了克服这个限制。TimeLord
通过取消当前计时器并将其替换为新计时器来启用“重置”计时器。
以此目的TimeLord
包含一个包装中间工作函数和一个“令牌”属性,必须由正在运行的计时器实例弹出才能执行指定的目标函数。
这种设计保证了指定目标函数的唯一执行,因为dict.pop()
是一个原子操作。timelord.reset()
只要当前计时器尚未启动其线程并弹出该计时器,该计时器就有效_token
。这种方法不能完全防止尝试“重置”时新计时器线程的潜在无效启动,但当发生这种情况时,它是一种不重要的冗余,因为目标函数只能执行一次。
此代码在 Python 2 和 3 上运行:
import time
from datetime import datetime
from threading import Timer, current_thread
def f(x):
print('{} {}: RUNNING TARGET FUNCTION'.format(
datetime.now(), current_thread().name)
)
time.sleep(x)
print('{} {}: EXITING'.format(datetime.now(), current_thread().name))
class TimeLord:
"""
Manager Class for threading.Timer instance. Allows "resetting" `interval`
as long execution of `function` has not started by canceling the old
and constructing a new timer instance.
"""
def worker(self, *args, **kwargs):
try:
self.__dict__.pop("_token") # dict.pop() is atomic
except KeyError:
pass
else:
self.func(*args, **kwargs)
def __init__(self, interval, function, args=None, kwargs=None):
self.func = function
self.args = args if args is not None else []
self.kwargs = kwargs if kwargs is not None else {}
self._token = True
self._init_timer(interval)
def _init_timer(self, interval):
self._timer = Timer(interval, self.worker, self.args, self.kwargs)
self._timer.daemon = True
def start(self):
self._timer.start()
print('{} {}: STARTED with `interval={}`'.format(
datetime.now(), self._timer.name, self._timer.interval)
)
def reset(self, interval):
"""Cancel latest timer and start a new one if `_token` is still there.
"""
print('{} {}: CANCELED'.format(datetime.now(), self._timer.name))
self._timer.cancel()
# reduces, but doesn't prevent, occurrences when a new timer
# gets created which eventually will not succeed in popping
# the `_token`. That's uncritical redundancy when it happens.
# Only one thread ever will be able to execute `self.func()`
if hasattr(self, "_token"):
self._init_timer(interval)
self.start()
def cancel(self):
self._timer.cancel()
def join(self, timeout=None):
self._timer.join(timeout=timeout)
def run_demo(initial_interval):
print("*** testing with initial interval {} ***".format(initial_interval))
tl = TimeLord(interval=initial_interval, function=f, args=(10,))
tl.start()
print('*** {} sleeping two seconds ***'.format(datetime.now()))
time.sleep(2)
tl.reset(interval=6)
tl.reset(interval=7)
tl.join()
print("-" * 70)
if __name__ == '__main__':
run_demo(initial_interval=5)
run_demo(initial_interval=2)
示例输出:
*** testing with initial interval 5 ***
2019-06-05 20:58:23.448404 Thread-1: STARTED with `interval=5`
*** 2019-06-05 20:58:23.448428 sleeping two seconds ***
2019-06-05 20:58:25.450483 Thread-1: CANCELED
2019-06-05 20:58:25.450899 Thread-2: STARTED with `interval=6`
2019-06-05 20:58:25.450955 Thread-2: CANCELED
2019-06-05 20:58:25.451496 Thread-3: STARTED with `interval=7`
2019-06-05 20:58:32.451592 Thread-3: RUNNING TARGET FUNCTION
2019-06-05 20:58:42.457527 Thread-3: EXITING
----------------------------------------------------------------------
*** testing with initial interval 2 ***
2019-06-05 20:58:42.457986 Thread-4: STARTED with `interval=2`
*** 2019-06-05 20:58:42.458033 sleeping two seconds ***
2019-06-05 20:58:44.458058 Thread-4: RUNNING TARGET FUNCTION
2019-06-05 20:58:44.459649 Thread-4: CANCELED
2019-06-05 20:58:44.459724 Thread-4: CANCELED
2019-06-05 20:58:54.466342 Thread-4: EXITING
----------------------------------------------------------------------
Process finished with exit code 0
请注意,当interval=2时,两秒后的取消没有效果,因为计时器已经在执行目标函数。