非阻塞文件读取 [英] Non-blocking file read

问题描述

如何在非阻塞模式下读取二进制文件或文本文件的内容?

How can I read the contents of a binary or a text file in a non-blocking mode?

对于二进制文件:当我open(filename, mode='rb')时，我得到一个io.BufferedReader的实例. io.BufferedReader.read 说的文档:

For binary files: when I open(filename, mode='rb'), I get an instance of io.BufferedReader. The documentation fort io.BufferedReader.read says:

读取并返回大小字节，或者如果未指定大小或为负数，则直到EOF或读取调用将在非阻塞模式下阻塞.

Read and return size bytes, or if size is not given or negative, until EOF or if the read call would block in non-blocking mode.

很明显，简单的open(filename, 'rb').read()处于阻止模式.令我惊讶的是，我在io文档的任何地方都找不到关于如何选择非阻塞模式的解释.

Obviously a straightforward open(filename, 'rb').read() is in a blocking mode. To my surprise, I could not find an explanation anywhere in the io docs of how to choose the non-blocking mode.

对于文本文件:当我open(filename, mode='rt')时，我得到io.TextIOWrapper.我假设相关文档是read在其基类io.TextIOBase中的文档；和根据这些文档，似乎没有办法完全不阻塞读取:

For text files: when I open(filename, mode='rt'), I get io.TextIOWrapper. I assume the relevant docs are those for read in its base class, io.TextIOBase; and according to those docs, there seems no way to do non-blocking read at all:

作为单个str从流中读取并返回最大大小的字符.如果size为负数或无，则读取直到EOF.

Read and return at most size characters from the stream as a single str. If size is negative or None, reads until EOF.

推荐答案

文件操作被阻止.没有非阻塞模式.

File operations are blocking. There is no non-blocking mode.

但是您可以创建一个在后台读取文件的线程.在Python 3中， concurrent.futures模块可以在这里有用.

But you can create a thread which reads the file in the background. In Python 3, concurrent.futures module can be useful here.

from concurrent.futures import ThreadPoolExecutor

def read_file(filename):
    with open(filename, 'rb') as f:
        return f.read()

executor = concurrent.futures.ThreadPoolExecutor(1)
future_file = executor.submit(read_file, 'C:\\Temp\\mocky.py')

# continue with other work

# later:

if future_file.done():
    file_contents = future_file.result()

或者，如果您需要在操作完成后调用回调:

Or, if you need a callback to be called when the operation is done:

def on_file_reading_finished(future_file):
    print(future_file.result())

future_file = executor.submit(read_file, 'C:\\Temp\\mocky.py')
future_file.add_done_callback(on_file_reading_finished)

# continue with other code while the file is loading...

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