如何在 python 中使用多线程将数据写入文本文件？

Question

我想在技术上使用 python 中的多线程将数据附加到同一个文本文件中

这是我的代码_

import threading
my_list = ["a", "b", "c", "d", "e", "f"]
def f1():
     for item in my_list:
       file = open("order_log.txt", "a")
       file.write(f"It is f1 {item}")
       file.close()
def f2():
     for item in my_list:
       file = open("order_log.txt", "a")
       file.write(f"It is f2 {item}")
       file.close()
def f3():
     for item in my_list:
       file = open("order_log.txt", "a")
       file.write(f"It is f3 {item}")
       file.close()
def f4():
     for item in my_list:
       file = open("order_log.txt", "a")
       file.write(f"It is f4 {item}")
       file.close()
t1 = threading.Thread(target=f1)
t2 = threading.Thread(target=f2)
t3 = threading.Thread(target=f3)
t4 = threading.Thread(target=f4)
t1.start()
t2.start()
t3.start()
t4.start()
t1.join()
t2.join()
t3.join()
t4.join()

但是当我执行程序时，它并没有写任何东西，谁能告诉我该怎么做。

Answer 1

您需要做到这一点，以便一次只有一个线程可以写入文件。这是通过让线程在文件上保存Lock 来完成的。一旦线程处理完文件，它就可以释放Lock，它会被等待它的线程之一占用。

这是一个如何使用锁的示例，以及Queue，因为您想要使用线程的原因通常是因为您想要对许多数据对象并行执行相同的操作。

import threading
import queue
import random
import time

tasks = queue.Queue()

output = open('output.txt', 'w')
output_lock = threading.Lock()

def worker(thread_number):
    while not tasks.empty():
        task = tasks.get()
        # perform long calculation here...
        time_to_spend = random.random()
        time.sleep(time_to_spend)
        result = task * task

        # now we have result, want to write it
        with output_lock:  # this will block until the lock is available
            print(thread_number, ': square of', task, 'is', result, '; took', time_to_spend, file=output)
        tasks.task_done()

for i in range(100):
    tasks.put(i)

for thread in range(8):
    threading.Thread(target=worker, args=(thread,)).start()

print('waiting for tasks to complete')
tasks.join()
print('done')

我得到的输出是：

6 : square of 6 is 36 ; took 0.02233345201885739
7 : square of 7 is 49 ; took 0.0352967148552743
4 : square of 4 is 16 ; took 0.1043699083780637
7 : square of 9 is 81 ; took 0.2158108589024338
1 : square of 1 is 1 ; took 0.3330501408298937
4 : square of 10 is 100 ; took 0.3564233912485101
5 : square of 5 is 25 ; took 0.8496825534757959
0 : square of 0 is 0 ; took 0.8807306770021203
4 : square of 13 is 169 ; took 0.4420943872313102
7 : square of 11 is 121 ; took 0.6772180132068408
5 : square of 14 is 196 ; took 0.1101644871869385
6 : square of 8 is 64 ; took 0.944739067078435
3 : square of 3 is 9 ; took 0.9699315957506418
2 : square of 2 is 4 ; took 0.9903787965119304
3 : square of 20 is 400 ; took 0.029847547355710158
1 : square of 12 is 144 ; took 0.696648284935379
...