迭代 Python 文件对象线程安全吗? [英] Is iterating over a Python file object thread safe?

问题描述

在寻找这个问题的巧妙解决方案时 我想知道对 Python 文件对象进行迭代是否是线程安全的.

While searching for a neat solution to this problem I was wondering if iterating over a Python file object is thread safe or not.

from concurrent.futures import ThreadPoolExecutor
import sys, time

f = open("big_file")

def worker():
    running = True
    while running:
        try:
            line = next(f)
        except StopIteration:
            return
        # process line
        time.sleep(3)
        sys.stdout.write(line + "\n")

no_workers = 4
with ThreadPoolExecutor(max_workers=no_workers) as e:
    for _ in range(no_workers):
        e.submit(worker)

f.close()

我的问题是，如果上面的例子是安全的，或者如果不是，有什么简单的方法可以获取线程安全的文件对象(对于逐行读取文件，不需要写入).

My question is, if the example above is safe, or if not, what is an easy way to get a thread-safe file object (for reading a file line by line, writing is not required).

推荐答案

不，文件 I/O 不是线程安全的.锁定是一种解决方案，但我认为让单个线程处理每个外部资源的选项效果更好.其他线程将工作请求发送到 Queue.Queue 实例上的专用线程(并提供他们自己的另一个队列，以防他们需要返回结果)，专用线程大部分时间都在等待在该队列上的 .get 上，每当它收到请求时，它都会处理它，可能会返回结果.

No, file I/O is not thread safe. Locking is a solution, but I think the option of having a single thread deal with each external resource works better. Other threads send work requests to the dedicated thread on a Queue.Queue instance (and provide another queue of their own in case they need result(s) back), the dedicated thread spends most of its time waiting on a .get on that queue and whenever it gets a request it deals with it, possibly returning the results.

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