python threading.timer set time limit when program runs out of time

问题

I have some questions related to setting the maximum running time of a function in Python. In fact, I would like to use pdfminer to convert the .pdf files to .txt.

The problem is that very often, some files are not possible to decode and take extremely long time. So I want to set threading.Timer() to limit the conversion time for each file to 5 seconds. In addition, I run under windows so I cannot use the signal module for this.

I succeeded in running the conversion code with pdfminer.convert_pdf_to_txt() (in my code it is "c"), but I am not sure that the in the following code, threading.Timer() works. (I don't think it properly constrains the time for each processing)

In summary, I want to:

Convert the pdf to txt
Time limit for each conversion is 5 sec, if it runs out of time, throw an exception and save an empty file
Save all the txt files under the same folder
If there are any exceptions/errors, still save the file but with empty content.

Here is the current code:

import converter as c
import os
import timeit
import time
import threading
import thread

yourpath = 'D:/hh/'

def iftimesout():
    print("no")

    with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
        newfile.write("")


for root, dirs, files in os.walk(yourpath, topdown=False):
    for name in files:
        try:
           timer = threading.Timer(5.0,iftimesout)
           timer.start()
           t=os.path.split(os.path.dirname(os.path.join(root, name)))[1]
           a=str(os.path.split(os.path.dirname(os.path.join(root, name)))[0])
           g=str(a.split("\\")[1])

           with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
                newfile.write(c.convert_pdf_to_txt(os.path.join(root, name)))
                print("yes")

           timer.cancel()

         except KeyboardInterrupt:
               raise

         except:
             for name in files:
                 t=os.path.split(os.path.dirname(os.path.join(root, name)))[1]
                 a=str(os.path.split(os.path.dirname(os.path.join(root, name)))[0])

                 g=str(a.split("\\")[1])
                 with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
                     newfile.write("")

回答1:

Check following code and let me know in case of any issues. Also let me know whether you still want to use force termination feature (KeyboardInterruption)

path_to_pdf = "C:\\Path\\To\\Main\\PDFs" # No "\\" at the end of path!
path_to_text = "C:\\Path\\To\\Save\\Text\\" # There is "\\" at the end of path!
TIMEOUT = 5  # seconds
TIME_TO_CHECK = 1  # seconds


# Save PDF content into text file or save empty file in case of conversion timeout
def convert(path_to, my_pdf):
    my_txt = text_file_name(my_pdf)
    with open(my_txt, "w") as my_text_file:
         try:
              my_text_file.write(convert_pdf_to_txt(path_to + '\\' + my_pdf))
         except:
              print "Error. %s file wasn't converted" % my_pdf


# Convert file_name.pdf from PDF folder to file_name.text in Text folder
def text_file_name(pdf_file):
    return path_to_text + (pdf_file.split('.')[0]+ ".txt")


if __name__ == "__main__":
    # for each pdf file in PDF folder
    for root, dirs, files in os.walk(path_to_pdf, topdown=False):
        for my_file in files:
            count = 0
            p = Process(target=convert, args=(root, my_file,))
            p.start()
            # some delay to be sure that text file created
            while not os.path.isfile(text_file_name(my_file)):
                time.sleep(0.001)
            while True:
                # if not run out of $TIMEOUT and file still empty: wait for $TIME_TO_CHECK,
                # else: close file and start new iteration
                if count < TIMEOUT and os.stat(text_file_name(my_file)).st_size == 0:
                    count += TIME_TO_CHECK
                    time.sleep(TIME_TO_CHECK)
                else:
                    p.terminate()
                    break

回答2:

I finally figured it out!

First of all, define a function to call another function with a limited timeout:

import multiprocessing

def call_timeout(timeout, func, args=(), kwargs={}):
    if type(timeout) not in [int, float] or timeout <= 0.0:
        print("Invalid timeout!")

    elif not callable(func):
        print("{} is not callable!".format(type(func)))

    else:
        p = multiprocessing.Process(target=func, args=args, kwargs=kwargs)
        p.start()
        p.join(timeout)

        if p.is_alive():
            p.terminate()
            return False
        else:
            return True

What does the function do?

Check timeout and function to be valid
Start the given function in a new process, which has some advantages over threads
Block the program for x seconds (p.join()) and allow the function to be executed in this time
After the timeout expires, check if the function is still running
- Yes: Terminate it and return False
- No: Fine, no timeout! Return True

We can test it with time.sleep():

import time

finished = call_timeout(2, time.sleep, args=(1, ))
if finished:
    print("No timeout")
else:
    print("Timeout")

We run a function which needs one second to finish, timeout is set to two seconds:

No timeout

If we run time.sleep(10) and set the timeout to two seconds:

finished = call_timeout(2, time.sleep, args=(10, ))

Result:

Timeout

Notice the program stops after two seconds without finishing the called function.

Your final code will look like this:

import converter as c
import os
import timeit
import time
import multiprocessing

yourpath = 'D:/hh/'

def call_timeout(timeout, func, args=(), kwargs={}):
    if type(timeout) not in [int, float] or timeout <= 0.0:
        print("Invalid timeout!")

    elif not callable(func):
        print("{} is not callable!".format(type(func)))

    else:
        p = multiprocessing.Process(target=func, args=args, kwargs=kwargs)
        p.start()
        p.join(timeout)

        if p.is_alive():
            p.terminate()
            return False
        else:
            return True

def convert(root, name, g, t):
    with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
        newfile.write(c.convert_pdf_to_txt(os.path.join(root, name)))

for root, dirs, files in os.walk(yourpath, topdown=False):
    for name in files:
        try:
           t=os.path.split(os.path.dirname(os.path.join(root, name)))[1]
           a=str(os.path.split(os.path.dirname(os.path.join(root, name)))[0])
           g=str(a.split("\\")[1])
           finished = call_timeout(5, convert, args=(root, name, g, t))

           if finished:
               print("yes")
           else:
               print("no")

               with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
                   newfile.write("")

        except KeyboardInterrupt:
             raise

       except:
           for name in files:
                t=os.path.split(os.path.dirname(os.path.join(root, name)))[1]
                a=str(os.path.split(os.path.dirname(os.path.join(root, name)))[0])

               g=str(a.split("\\")[1])
               with open("D:/f/"+g+"&"+t+"&"+name+".txt", mode="w") as newfile:
                   newfile.write("")

The code should be easy to understand, if not, feel free to ask.

I really hope this helps (as it took some time for us to get it right ;))!

来源：https://stackoverflow.com/questions/40748555/python-threading-timer-set-time-limit-when-program-runs-out-of-time

标签

python

multithreading

timer

timeout