我想創建一個程式，它每隔一段時間執行一些任務，比如每 4 秒，但這應該使用多個執行緒來完成，這些執行緒輪流完成，每個執行緒執行一個任務，然后允許另一個執行下一個任務。
如果每 4 秒列印一次是我想要執行的任務，那么事件順序可能如下所示。
Thread 1 printed at 0 seconds
Thread 2 printed at 4 seconds
Thread 3 printed at 8 seconds
Thread 1 printed at 12 seconds
...
我通過存盤執行緒 ID 的佇列來解決這個問題，并將佇列的第一個元素視為應該執行任務的下一個執行緒的 ID。當一個執行緒執行任務時，佇列會旋轉，以便另一個執行緒接下來執行該任務。自上次任務完成以來的時間是在每個執行緒的每次迭代中計算的，用于確定執行緒是否應該執行任務（以及輪到當前執行緒）。
這是代碼
from threading import Thread, Lock
import threading
from collections import deque
from datetime import datetime
import time
mutex = Lock()
print_interval = 4.0
thread_queue = deque([])
running = True
def print_thread():
last_print_time = datetime.now()
while running:
mutex.acquire()
delta_time = (datetime.now() - last_print_time).total_seconds()
if delta_time >= print_interval and threading.get_ident() == thread_queue[0]:
last_print_time = datetime.now()
thread_queue.rotate(1)
print('Thread {} printing at time {}'.format(threading.get_ident(), datetime.now().time()), flush=True)
mutex.release()
threads = []
for i in range(4):
thread = Thread(target = print_thread)
thread.start()
thread_queue.append(thread.ident)
time.sleep(10)
running = False
for thread in threads:
thread.join()
這是一個輸出示例。
Thread 29548 printing at time 17:11:50.662538
Thread 34616 printing at time 17:11:50.683628
Thread 35900 printing at time 17:11:50.683628
Thread 27924 printing at time 17:11:50.683628
Thread 29548 printing at time 17:11:54.667393
Thread 34616 printing at time 17:11:54.683969
Thread 35900 printing at time 17:11:54.683969
而不是執行緒等待正確的時間過去，由于某種原因，delta_time 計算在背景關系切換時爆炸并且執行緒立即執行任務，僅在所有執行緒完成任務時才暫停。我的邏輯在這里正確嗎？我不確定出了什么問題。
謝謝。
編輯：我將解釋我認為 print_thread 應該如何分步運行并盡量弄清楚它。假設我們有 2 個執行緒，ID 分別為 1 和 2，執行緒佇列看起來像 [1,2]（執行緒 1 先行）
Thread 1 acquires the lock
delta_time is < 4
conditional fails to execute
Thread 1 releases the lock
Thread 2 acquires the lock
delta_time is < 4
conditional fails to execute
Thread 2 releases the lock
This goes on for about 4 seconds...
Thread 1 acquires the lock
delta_time is 4.1
conditional is true because delta_time is >= 4 and this thread is at the front of the queue
last_print_time = current time
rotate queue (thread 2 will be next)
Thread 1 releases the lock
Thread 2 acquires the lock
delta_time is 0.01
conditional fails because not enough time has passed
Thread 2 releases the lock
抱歉，如果這很冗長，但這基本上是我所期望的流程以及為什么執行緒應該按順序執行，而不是一次執行。
uj5u.com熱心網友回復：
至于我的主要問題是每個執行緒都使用自己的私有執行緒last_print_time，并且它不會last_print_time在其他執行緒中重置。
你將不得不使用global last_print_time
帶有全域變數的完整代碼。
我設定更長的時間sleep()來查看結果。
from threading import Thread, Lock
import threading
from collections import deque
from datetime import datetime
import time
mutex = Lock()
print_interval = 4.0
thread_queue = deque([])
running = True
last_print_time = datetime.now()
def print_thread():
global last_print_time
while running:
mutex.acquire()
delta_time = (datetime.now() - last_print_time).total_seconds()
if delta_time >= print_interval and threading.get_ident() == thread_queue[0]:
last_print_time = datetime.now()
thread_queue.rotate(1)
print('Thread {} printing at time {}'.format(threading.get_ident(), datetime.now().time()), flush=True)
mutex.release()
threads = []
for i in range(4):
thread = Thread(target = print_thread)
thread.start()
thread_queue.append(thread.ident)
time.sleep(30)
running = False
for thread in threads:
thread.join()
結果：
Thread 140276746778368 printing at time 19:40:20.012389
Thread 140276517566208 printing at time 19:40:24.015615
Thread 140276729992960 printing at time 19:40:28.021712
Thread 140276738385664 printing at time 19:40:32.037404
Thread 140276746778368 printing at time 19:40:36.038693
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