화구는 셋뿐: 동기화 도구

import threading
import time

stoves = threading.Semaphore(3)         # 화구는 셋
start = time.perf_counter()

def cook(name):
    with stoves:                        # 빈 화구가 날 때까지 기다렸다가 잡는다
        print(f"{time.perf_counter() - start:.1f}s {name} on")
        time.sleep(0.3)

names = [f"cook{i}" for i in range(1, 7)]
threads = [threading.Thread(target=cook, args=(n,)) for n in names]
for th in threads:
    th.start()
for th in threads:
    th.join()
print(f"total {time.perf_counter() - start:.2f}s")
# 예:
# 0.0s cook1 on
# 0.0s cook2 on
# 0.0s cook3 on
# 0.3s cook4 on
# 0.3s cook5 on
# 0.3s cook6 on
# total 0.60s

loose = threading.Semaphore(3)
loose.release()                         # 실수로 한 번 더 놓았다
print(sum(loose.acquire(blocking=False) for _ in range(10)))   # 화구가 넷이 됐다
# 4

strict = threading.BoundedSemaphore(3)
strict.release()
# ValueError: Semaphore released too many times

opened = threading.Event()              # 처음엔 꺼져 있다
start = time.perf_counter()

def cook(name):
    opened.wait()                       # 신호가 켜질 때까지 기다린다
    print(f"{time.perf_counter() - start:.1f}s {name} fire")

threads = [threading.Thread(target=cook, args=(n,)) for n in ["minho", "sua", "tak"]]
for th in threads:
    th.start()
time.sleep(0.5)
print(opened.is_set())
opened.set()                            # "오픈!"
for th in threads:
    th.join()
print(opened.is_set())
# False
# 0.5s minho fire     (세 줄의 순서는 실행마다 다르다)
# 0.5s sua fire
# 0.5s tak fire
# True

closing = threading.Event()
print(closing.wait(timeout=0.2))        # 0.2초 기다렸는데 신호가 없다
closing.set()
print(closing.wait(timeout=0.2))        # 이미 켜져 있으면 바로 True
closing.clear()                         # 다시 끈다
print(closing.is_set())
# False
# True
# False

pantry = []                             # 재료 선반(공유 상태)
arrived = threading.Condition()         # 선반을 지키는 잠금 + "깨워 줘" 명단
start = time.perf_counter()

def cook(name, need):
    with arrived:
        ok = arrived.wait_for(lambda: need in pantry, timeout=0.5)
        print(f"{time.perf_counter() - start:.1f}s {name} {need if ok else 'gave up'}")

def supplier():
    for item in ["tofu", "egg"]:        # 생선은 오늘 안 온다
        time.sleep(0.1)
        with arrived:
            pantry.append(item)
            arrived.notify_all()        # 기다리는 사람을 모두 깨운다

threads = [threading.Thread(target=cook, args=a) for a in [("minho", "egg"), ("sua", "tofu"), ("tak", "fish")]]
threads.append(threading.Thread(target=supplier))
for th in threads:
    th.start()
for th in threads:
    th.join()
# 0.1s sua tofu
# 0.2s minho egg
# 0.5s tak gave up

plates = 0
counter = threading.Condition()

def cook():
    global plates
    time.sleep(0.1)
    with counter:
        plates += 1
        counter.notify()                # 기다리는 사람 하나만 깨운다

def waiter(name):
    global plates
    with counter:
        counter.wait_for(lambda: plates > 0)
        plates -= 1
        print(name, "took a plate")

ws = [threading.Thread(target=waiter, args=(n,)) for n in ["w1", "w2"]]
cs = [threading.Thread(target=cook) for _ in range(2)]
for th in ws + cs:
    th.start()
for th in ws + cs:
    th.join()
print(plates)
# 예:
# w1 took a plate
# w2 took a plate
# 0

start = time.perf_counter()
table = threading.Barrier(4, action=lambda: print("serve 4 plates"))
done = []

def cook(name, sec):
    time.sleep(sec)                     # 각자 속도가 다르다
    i = table.wait()                    # 넷이 다 올 때까지 패스 앞에서 기다린다
    done.append((round(time.perf_counter() - start, 1), i, name))

crew = [("minho", 0.1), ("sua", 0.2), ("chef", 0.3), ("tak", 0.4)]
threads = [threading.Thread(target=cook, args=c) for c in crew]
for th in threads:
    th.start()
for th in threads:
    th.join()
print(sorted(done))
# serve 4 plates
# [(0.4, 0, 'minho'), (0.4, 1, 'sua'), (0.4, 2, 'chef'), (0.4, 3, 'tak')]

opened = threading.Event()
stoves = threading.Semaphore(3)
lock = threading.Lock()
on_fire = peak = 0
log = []
start = time.perf_counter()

def cook(n):
    global on_fire, peak
    opened.wait()                       # 1. "오픈!" 전에는 불을 켜지 않는다
    with stoves:                        # 2. 화구는 동시에 셋까지
        with lock:
            on_fire += 1
            peak = max(peak, on_fire)
        time.sleep(0.3)
        with lock:
            on_fire -= 1
            log.append((round(time.perf_counter() - start, 1), f"#{n}"))

threads = [threading.Thread(target=cook, args=(n,)) for n in range(1, 7)]
for th in threads:
    th.start()
time.sleep(0.3)                         # 손님 맞을 준비
opened.set()
for th in threads:
    th.join()
print(sorted(log))
print(f"peak {peak}, total {time.perf_counter() - start:.2f}s")
# 예:
# [(0.6, '#1'), (0.6, '#2'), (0.6, '#3'), (0.9, '#4'), (0.9, '#5'), (0.9, '#6')]
# peak 3, total 0.90s