[PYTHON] Implement a thread that can be paused by exploiting yield

Suppose you have an ordinary subroutine

def foo():
  print("foo")
  print("bar")

foo () # Output "foo" and "bar"

Divide by inserting yield in this

def foo():
  print("foo")
  yield 0
  print("bar")
  yield 0

f = foo()

f.next () # Output "foo" f.next () # Output "bar"

In other words, make one process an iterator with yield If you apply this to Thread, you can implement pause / resume / suspend (pause / resume / halt method).

class Shred(Thread):
	def __init__(actions):
		Thread.__init__()
		self._actions = actions
		self.is_halted = False
		self.is_paused = False

	def run():
		while True:
			if self.is_paused:
				continue
			if self.is_halted:
				return
			try:
				self._actions.__next__()
			except StopIteration:
				self.is_halted = True
				return

	def pause():
		self.is_paused = True

	def resume():
		self.is_paused = False

	def halt():
		self.is_halted = True

(Actually it is better to use ʻEventfor the flag) This allows the pause / resume / suspend chokepoints to be represented only inyield`. In addition to improving readability, you can focus on writing other logic

def baz():
	for n in range(10):
		print(n)
		time.sleep(1)
		yield 0

s = Shred(baz())
s.start()
time.sleep(2)
#  0
#  1
#  2
s.pause()
time.sleep(2)

No output for 2 seconds

s.resume()
time.sleep(2)
#  3
#  4
#  5
s.halt()

#End of output

By the way, this iterator will return to the original subroutine after executing all the contents.

list(baz())
#  0
#  1
#  2
#  ...
#  9

I came up with the idea, but I didn't actually use it for the following reasons.

--Maximum surprise ――Mostly it will be implemented normally later ――It is discouraging to actively utilize side effects ――I feel like I'm playing with the language and I'm angry ――I mean, no one is hitting such a low-level API these days.

So I don't know how helpful it is, but that's it