"""
Producer-consumer example (multiple consumers)
"""
# MCS 260 Fall 2021 Lecture 39 (add-on example posted after lecture)
import threading
import time
import random

class WorkerThread(threading.Thread):
    """
    Thread that does work in the background, taking jobs from
    a specified stack (realized as a Python list)
    """
    def __init__(self,stack,stacklock,workernumber=0):
        """
        Make a new worker that receives its work from
        a list `stack`
        """
        super().__init__()
        self.workernumber = workernumber
        self.stack = stack
        self.stacklock = stacklock
        self.idstr = "Worker {}".format(self.workernumber)

    def run(self):
        "Main work of the thread"
        while True:
            self.stacklock.acquire()
            if self.stack:   # really tests "if self.stack is not empty"
                time.sleep(0.1)
                x = self.stack.pop()
                self.stacklock.release()
                if x == None:
                    print(self.idstr,"shutting down on request")
                    break
                print(self.idstr,"now working on {}".format(x),flush=True)
                time.sleep(2*random.random())
                print(self.idstr,"finished job {}".format(x),flush=True)
            else:
                # no work to do, take a short break
                self.stacklock.release()
                print(self.idstr,"is idle right now")
                time.sleep(0.5)

jobstack = []
jobstack_lock = threading.Lock()

num_workers = 10
num_jobs = 30

print("Starting {} worker threads".format(num_workers))
workers = [ WorkerThread(jobstack,jobstack_lock,i) for i in range(num_workers) ]
for T in workers:
    T.start()

for i in range(num_jobs):
    print("Submit job {}".format(i),flush=True)
    jobstack_lock.acquire()
    jobstack.append(i) # is basically a push()
    jobstack_lock.release()
    if random.random() < 0.25:
        # 25 % chance we pause
        time.sleep(0.5 + 2.5*random.random())

print("Adding None(s) to the queue so the worker quits when done")

# We need to add `num_workers` copies of None to the queue so that
# each thread gets one.  (Could handle this in other ways, e.g. by
# setting an attribute of each thread that signals completion.)
for _ in range(num_workers):
    jobstack.insert(0,None)  # NOTE: inefficient