时间休眠导致的不一致错误？

Question

为了练习，我编写了一个小Python脚本，在这个脚本中我计算出给定值的所有素数。但我遇到了一些不一致的错误

首先是代码：

import datetime
import time
import threading
class myThread (threading.Thread):
  def __init__(self, threadID, name, threadcounter):
    threading.Thread.__init__(self)
    self.threadID = threadID
    self.name = name
    self.threadcounter = threadcounter
  def run(self):
    delete_non_primes (self.threadcounter)
print ('This script outputs all primes until the given value. \nWhat value shall be calculated until? ')
maxval = int(input("Please enter the wanted value: "))
print ('Preparing...')
primes = []
primes.append(0)
primes.append(0)
primes.append(2)
i = 3
for i in range (3,maxval+1):
  primes.append(i)
if primes[3]!=3:
  import sys
  sys.exit("An error occured.")
counter = 1
percent = 0
thread1 = myThread(1, "Thread-1 iniated", 0)
thread2 = myThread(2, "Thread-2 iniated", 0)
thread3 = myThread(3, "Thread-3 iniated", 0)
thread4 = myThread(4, "Thread-4 iniated", 0)
thread5 = myThread(5, "Thread-5 iniated", 0)
nr_of_threads = 0
def delete_non_primes ( prime ):
  if prime != 0:
    breaker = prime
    while (breaker < maxval):
      breaker = breaker +1
      if primes[breaker] != 0:
        if primes [prime] != 0:
          if (primes[breaker] % primes[prime]) == 0:
            primes[breaker] = 0      
print ("Preparation done.")
print ("Calculating...")
start = datetime.datetime.now()
while (counter < maxval ):
  if counter < maxval:
    counter = counter +1
    thread1 = myThread(1, "Thread-1", counter)
    thread1.start()
  if counter < maxval:
    counter = counter +1
    thread2 = myThread(2, "Thread-2", counter)
    thread2.start()
  if counter < maxval:
    counter = counter +1
    thread3 = myThread(3, "Thread-3", counter)
    thread3.start()
  if counter < maxval:
    counter = counter +1
    thread4 = myThread(4, "Thread-4", counter)
    thread4.start()
  if counter < maxval:
    counter = counter +1
    thread5 = myThread(5, "Thread-5", counter)
    thread5.start()
  thread1.join()
  thread2.join()
  thread3.join()
  thread4.join()
  thread5.join()
#This time.sleep() seems to make the code consistent
  time.sleep(0.05)
  if (counter*100)//maxval > percent:
    percent = (counter*100)//maxval
    print (str(percent) + "%")
end = datetime.datetime.now()
time_needed = end-start
print("\nPrimes to the given max value:")
j = 0
val = 0
while (j <maxval):
  j = j+1
  if primes[j] != 0:
    val = val+1
    if val < 1000000:
      valstr = str(val) + "      "
    if val < 100000:
      valstr = valstr + " "
    if val < 10000:
      valstr = valstr + " "
    if val < 1000:
      valstr = valstr + " "
    if val < 100:
      valstr = valstr + " "
    if val < 10:
      valstr = valstr + " "
    print ( str(valstr) + str(primes[j]))
print ("Time needed for calculation: " + str(time_needed))
print("All primes noted. Script ends.")

有时发生的错误是

"Traceback (most recent call last):

File "python", line 58, in

RuntimeError: can't start new thread"

如果我不使用时间。睡眠（0.05）。
它并不总是同一个线程，如果我使用它，我不会收到任何错误。因为这个脚本中有很多计算，所以没有这个语句会更好