Synchronization in Python

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Mutex checker problem

The unsynchronized program is:

class Shared:
    def __init__(self, end=10):
        self.counter = 0
        self.end = end
        self.array = [0] * self.end
 
def child_code(shared):
    while True:
        if shared.counter >= shared.end:
            break
        shared.array[shared.counter] += 1
        shared.counter += 1

If everything works correctly, each entry in array should be incremented exactly once.

Exercise

Add synchronization code to this program to enforce exclusive access to the shared variables.

The coke machine problem

The program simulates producers and consumers adding and removing cokes from a machine:

import random
 
class Shared:
    def __init__(self, start=5):
        self.cokes = start
 
def consume(shared):
    shared.cokes -= 1
    print(shared.cokes)
 
def produce(shared):
    shared.cokes += 1
    print(shared.cokes)
 
def loop(shared, f, mu=1):
    while True:
        t = random.expovariate(1.0 / mu)
        time.sleep(t)
        f(shared)

The machine capacity is 10 cokes, and it starts half full.

Exercise

Add code to this program to enforce the following synchronization constraints:

1. Access to cokes should be mutually exclusive.
2. If the number of cokes is zero, consumers should block until a coke is added.
3. If the number of cokes is 10, producers should block until a coke is removed.