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多线程使我收到“ ValueError:对已关闭文件的I / O操作”错误为什么?

如何解决多线程使我收到“ ValueError:对已关闭文件的I / O操作”错误为什么?

我正在使用WTForms编写Flask Web应用程序。在其中一种形式中,用户上传一个csv文件,服务器将分析收到的数据。这是我正在使用的代码

filename = token_hex(8) + '.csv'  # Generate a new filename
form.dataset.data.save('myapp/datasets/' + filename)  # Save the received file
dataset = genfromtxt('myapp/datasets/' + filename,delimiter=',')  # Open the newly generated file
# analyze 'dataset' 

只要我在单线程应用程序中使用此代码,一切就可以正常工作。我尝试在代码添加线程。这是线程调用的过程(与函数内部相同的代码):

def execute_analysis(form):
    filename = token_hex(8) + '.csv'  # Generate a new filename
    form.dataset.data.save('myapp/datasets/' + filename)  # Save the received file
    dataset = genfromtxt('myapp/datasets/' + filename,')  # Open the newly generated file
    # analyze 'dataset'

这是我如何调用线程

import threading

@posts.route("/estimation",methods=['GET','POST'])
@login_required
def estimate_parameters():
    form = EstimateForm()
    if form.validate_on_submit():
        threading.Thread(target=execute_analysis,args=[form]).start()
        flash("Your request has been received. Please check the site in again in a few minutes.",category='success')
        # return render_template('posts/post.html',title=post.id,post=post)
    return render_template('estimations/estimator.html',title='New Analysis',form=form,legend='New Analysis')

但是现在我收到以下错误

ValueError:已关闭文件的I / O操作。

相对于save函数调用。为什么不起作用?我该如何解决

解决方法

我对框架的了解不足以确切说明发生了什么,但是我可以告诉您如何解决它。

只要您拥有由多个线程共享的资源,就使用锁。

Array
(
    [0] => WC_Meta_Data Object
        (
            [current_data:protected] => Array
                (
                    [id] => 646
                    [key] => yith_booking_data
                    [value] => Array
                        (
                            [from] => 1603152000
                            [to] => 1603411200
                            [duration] => 3
                            [person_types] => Array
                                (
                                )

                            [booking_services] => Array
                                (
                                )

                            [booking_service_quantities] => Array
                                (
                                )

                            [_added-to-cart-timestamp] => 1602161920
                        )

                )

            [data:protected] => Array
                (
                    [id] => 646
                    [key] => yith_booking_data
                    [value] => Array
                        (
                            [from] => 1603152000
                            [to] => 1603411200
                            [duration] => 3
                            [person_types] => Array
                                (
                                )

                            [booking_services] => Array
                                (
                                )

                            [booking_service_quantities] => Array
                                (
                                )

                            [_added-to-cart-timestamp] => 1602161920
                        )

                )

        )

    [1] => WC_Meta_Data Object
        (
            [current_data:protected] => Array
                (
                    [id] => 647
                    [key] => _booking_id
                    [value] => 882
                )

            [data:protected] => Array
                (
                    [id] => 647
                    [key] => _booking_id
                    [value] => 882
                )

        )

)
Array
(
    [0] => WC_Meta_Data Object
        (
            [current_data:protected] => Array
                (
                    [id] => 451
                    [key] => yith_booking_data
                    [value] => Array
                        (
                            [from] => 1600905600
                            [to] => 1600992000
                            [duration] => 1
                            [person_types] => Array
                                (
                                )

                            [booking_services] => Array
                                (
                                )

                            [booking_service_quantities] => Array
                                (
                                )

                            [_added-to-cart-timestamp] => 1600955166
                        )

                )

            [data:protected] => Array
                (
                    [id] => 451
                    [key] => yith_booking_data
                    [value] => Array
                        (
                            [from] => 1600905600
                            [to] => 1600992000
                            [duration] => 1
                            [person_types] => Array
                                (
                                )

                            [booking_services] => Array
                                (
                                )

                            [booking_service_quantities] => Array
                                (
                                )

                            [_added-to-cart-timestamp] => 1600955166
                        )

                )

        )

    [1] => WC_Meta_Data Object
        (
            [current_data:protected] => Array
                (
                    [id] => 452
                    [key] => _booking_id
                    [value] => 709
                )

            [data:protected] => Array
                (
                    [id] => 452
                    [key] => _booking_id
                    [value] => 709
                )

        )

)

Documentation on threading.Lock

实现原始锁对象的类。线程获得锁后,随后的尝试将其阻塞,直到释放为止

基本上,在线程1调用from threading import Lock LOCK = Lock() def process(): LOCK.acquire() ... # open a file,write some data to it etc. LOCK.release() # alternatively,use the context manager syntax with LOCK: ... threading.Thread(target=process).start() threading.Thread(target=process).start() 之后,随后的调用例如来自其他线程的操作,将导致这些线程冻结并等待直到有人调用LOCK.acquire()(通常是线程1,在完成与资源的业务之后)。

如果文件名是随机生成的,那么我不会期望1个线程关闭另一个文件的问题,除非两个文件碰巧都生成了相同的名称。但是也许您可以通过一些实验来弄清楚,例如首先尝试锁定对LOCK.release()save的调用,然后检查是否有帮助。添加一些genfromtxt语句(或者甚至更好,使用print)也可能是有意义的,例如检查文件名是否不冲突。

,

没有进一步的上下文很难说,但我怀疑您可能是从函数返回或退出上下文管理器,这导致某些文件描述符关闭,从而导致save(..)调用失败ValueError

如果是这样,一种直接的解决方法是在返回/关闭文件之前等待线程完成。类似于:

def handle_request(form):
  ...
  analyzer_thread = threading.Thread(target=execute_analysis,args=[form])
  analyzer_thread.start() 
  ...
  analyzer_thread.join() # wait for completion of execute_analysis
  cleanup_context(form)
  return

以下是我正在描述的问题的可复制的最小示例:

import threading

SEM = threading.Semaphore(0)

def run(fd):
    SEM.acquire() # wait till release
    fd.write("This will fail :(")

fd = open("test.txt","w+")
other_thread = threading.Thread(target=run,args=[fd])
other_thread.start()

fd.close()
SEM.release() # release the semaphore,so other_thread will acquire & proceed
other_thread.join()

请注意,根据您的情况,主线程将关闭文件,而另一个线程将在用write进行ValueError: I/O operation on closed file.调用时失败。

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