アクセスの競合状態

withdrawやdepositを同時に行った場合、データの不整合が発生する可能性がある。これをデータの競合状態という。

class BankAccount(ABC):

    balance: float

    def __init__(self, balance: float = 0):
        self.balance: float = balance

    # @abstractmethod
    def deposit(self, amount: float) -> None:
        ...

    # @abstractmethod
    def withdraw(self, amount: float) -> None:
        ...

import sys
import time
from threading import Thread
import typing as T

from bank_account import BankAccount
from unsynced_bank_account import UnsyncedBankAccount

THREAD_DELAY = 1e-16

class ATM(Thread):
    def __init__(self, bank_account: BankAccount):
        super().__init__()
        self.bank_account = bank_account

    def transaction(self) -> None:
        self.bank_account.deposit(10)
        time.sleep(0.001)
        self.bank_account.withdraw(10)

    def run(self) -> None:
        self.transaction()

def test_atms(account: BankAccount, atm_number: int = 1000) -> None:
    atms: T.List[ATM] = []
    for _ in range(atm_number):
        atm = ATM(account)
        atms.append(atm)
        atm.start()

    for atm in atms:
        atm.join()

if __name__ == "__main__":
    atm_number = 1000
    sys.setswitchinterval(THREAD_DELAY)

    account = UnsyncedBankAccount()
    test_atms(account, atm_number=atm_number)

    print("Balance of unsynced account after concurrent transactions:")
    print(f"Actual : {account.balance}\nExpected: 0")

from bank_account import BankAccount

class UnsyncedBankAccount(BankAccount):
    def deposit(self, amount: float) -> None:
        if amount > 0:
            self.balance += amount
        else:
            raise ValueError("You can't deposit a negative amount of money")

    def withdraw(self, amount: float) -> None:
        if 0 < amount <= self.balance:
            self.balance -= amount
        else:
            raise ValueError("Account does not have sufficient funds")