threadlimiter.py

from threading import Lock, Condition


class ThreadLimiter:
    def __init__(self, maxvalue):
        self.maxvalue = maxvalue
        self.currentvalue = 0
        self.mainlock = Lock()
        self.maincond = Condition(self.mainlock)

    def setmax(self, maxval):
        self.mainlock.acquire()
        self.maxvalue = maxval
        self.maincond.notifyAll()
        self.mainlock.release()

    def acquire(self):
        self.mainlock.acquire()
        while True:
            if self.maxvalue > self.currentvalue:
                self.currentvalue += 1
                self.mainlock.release()
                return
            self.maincond.wait()

    def release(self):
        self.mainlock.acquire()
        self.currentvalue -= 1
        self.maincond.notify(1)
        self.mainlock.release()

    def __enter__(self):
        self.acquire()

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.release()