#!/usr/bin/env python3
"""
Lamport Bakery Algorithm – Python demo
运行：python bakery_demo.py
"""
import threading
import time
import random

N_THREADS = 10            # 线程数（顾客数）
CRITICAL_PER_THREAD = 3   # 每个线程想进多少次临界区

# 全局同步变量
choosing = [False] * N_THREADS
number   = [0]        * N_THREADS

# 一个所有线程都会修改的共享资源，用来验证互斥
shared_counter = 0

# -------------------------------------------------
def lamport_bakery_enter(i: int):
    """线程 i 申请进入临界区（门口排队）"""
    # 1. 取号
    choosing[i] = True
    # 模拟“原子”地找最大号码；Python GIL 让这句足够安全
    number[i] = max(number) + 1
    choosing[i] = False

    # 2. 门口等待：对所有其它线程按规则比较
    for j in range(N_THREADS):
        if j == i:
            continue
        # 2a 等对方取号完毕
        while choosing[j]:
            time.sleep(0.0001)  # 让出 CPU，减少忙等功耗
        # 2b 等对方号码更大 或 已退出
        while number[j] != 0 and (number[j], j) < (number[i], i):
            time.sleep(0.0001)

def lamport_bakery_exit(i: int):
    """线程 i 离开临界区（叫号完成）"""
    number[i] = 0

# -------------------------------------------------
def thread_worker(i: int):
    """每个线程的生命周期"""
    global shared_counter
    for _ in range(CRITICAL_PER_THREAD):
        # 请求进入
        lamport_bakery_enter(i)

        # ====== 临界区开始 ======
        old = shared_counter
        # 人为加一点随机延迟，放大竞态窗口
        time.sleep(random.uniform(0.01, 0.05))
        shared_counter = old + 1
        print(f"[Thread-{i}]  in CS  -> shared_counter={shared_counter}")
        # ====== 临界区结束 ======

        # 退出
        lamport_bakery_exit(i)
        # 非临界区随便睡
        time.sleep(random.uniform(0.01, 0.03))

# -------------------------------------------------
if __name__ == "__main__":
    threads = []
    for idx in range(N_THREADS):
        t = threading.Thread(target=thread_worker, args=(idx,))
        threads.append(t)

    start = time.time()
    for t in threads:
        t.start()
    for t in threads:
        t.join()
    end = time.time()

    print("\nAll done. Final counter =", shared_counter)
    print("Elapsed {:.2f}s".format(end - start))

[Thread-0]  in CS  -> shared_counter=1
[Thread-1]  in CS  -> shared_counter=2
[Thread-2]  in CS  -> shared_counter=3
...
[Thread-9]  in CS  -> shared_counter=30

All done. Final counter = 30
Elapsed 0.63s