FifoLock.py

import threading
import queue
import time

class Program:
    def __init__(self):
        self.queue = queue.Queue()
        
        self.pipeline = Pipeline(self)
        self.web = Webserver(self)
    
    def mainloop(self):
        while True:
            task = self.queue.get()
            task.run()

class FifoLock:
    def __init__(self, program):
        self.program = program
        self.queue = self.program.queue
        self.condition = threading.Condition()
    
    # blocks until run() is called
    def __enter__(self):
        # equivalent to .acquire() ?
        self.condition.__enter__()
        
        self.queue.put(self)
        self.condition.wait()
    
    def __exit__(self, *exc_info):
        self.condition.notify_all()
        
        # equivalent to .release() ?
        self.condition.__exit__(*exc_info)
    
    # releases self from __enter__()
    # blocks until __exit__()
    def run(self):
        with self.condition:
            self.condition.notify_all()
            self.condition.wait()s

class Pipeline:
    def __init__(self, program):
        self.program = program
        self.lock = FifoLock(self.program)
    
    def run(self):
        print("schedule p")
        with self.lock:
            print("pipeline")
            for x in range(3):
                print("p", x)
                time.sleep(.5)
            print("p exit")
    
    def mainloop(self):
        while True:
            self.run()

class Webserver:
    def __init__(self, program):
        self.program = program
        self.lock = FifoLock(self.program)
    
    def run(self):
        print("schedule w")
        with self.lock:
            print("web")
            for x in range(3):
                print("w", x)
                time.sleep(.51234)
            print("w exit")

p = Program()
threading.Thread(target=p.mainloop).start()
time.sleep(1)
threading.Thread(target=p.pipeline.mainloop).start()
time.sleep(5.34)
threading.Thread(target=p.web.run).start()
time.sleep(3.789)
threading.Thread(target=p.web.run).start()
time.sleep(5)
import os
os.abort()


# Below is a runthrough

$ python FifoLock.py 
schedule p
pipeline
p 0
p 1
p 2
p exit
schedule p
pipeline
p 0
p 1
p 2
p exit
schedule p
pipeline
p 0
p 1
p 2
p exit
schedule p
pipeline
p 0
p 1
schedule w
p 2
p exit
schedule p
web
w 0
w 1
w 2
w exit
pipeline
p 0
p 1
p 2
p exit
schedule p
pipeline
p 0
schedule w
p 1
p 2
p exit
schedule p
web
w 0
w 1
w 2
w exit
pipeline
p 0
p 1
p 2
p exit
schedule p
pipeline
p 0
p 1
Aborted (core dumped)