How to make while loop in python that is reliable enough for packet generator

Question

I'm making a packet generator and it's crucial to be able to send packets as steadily and as accurately as possible. The problem I'm having is that I send the packets using a while loop with time.sleep that is supposed to loop hundreds times/second, but since it takes additional and varying time to go through the loop it's hard to set a right sleeping time.

Here is the code I'm using:

while status == "1":
     try:
         s.send(message)
         data = s.recv(1500)
         status = self.clientstatus
         time.sleep(1.0 / (speed*100))
     except:
         status = "0"

EDIT:

Here is a working solution that I used

    def clientstart(self):
      self.sch = sched.scheduler(time.time, time.sleep)
      self.next_time = time.time()
      self.sch.enterabs(self.next_time, 0, self.oneround, ())

      self.reset.emit()
      time.sleep(0.03)

      n = 0
      targetip = self.entry1.text()
      host = targetip
      port = 5001
      speed = int(self.entry2.text())
      self.delay = 1.0 / (speed*100)

      if targetip:
              self.s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
              try:
                    self.s.connect((host,port))
              except:
                    self.err1.emit(1)
                    n = n+1
              openfile = open('1024')
              self.message = openfile.read()
              self.clientstatus = "1"
              status = self.clientstatus
              self.buttonswitch("2")
              n = n+1
              self.nn = 1
              t = threading.Thread(target = self.temp)
              t.setDaemon(True)
              t.start()
              self.err1.emit(2)
              self.sch.run()

              if n == 1:
                    self.err1.emit(4)
              elif n == 4:
                    self.err1.emit(0)
              self.s.close()
              self.buttonswitch("3")
      else:
              self.err1.emit(3)

    def oneround(self):
      try:
        self.s.send(self.message)
        status = self.clientstatus
        self.nn += 1
        if status == '1':
            self.next_time += self.delay
            self.sch.enterabs(self.next_time, 0, self.oneround, ())
      except:
        pass

using self with socket might cause some problems in the future though

Alex Martelli · Accepted Answer · 2015-02-01 03:27:15Z

3

One of the soundest ways to schedule periodic events, as close to regularly as a system that's of course not real-time will allow, is the sched module documented at https://docs.python.org/2/library/sched.html .

For your use case, I'd try:

import sched, time
sch = sched.scheduler(time.time, time.sleep)

delay = 1.0 / (speed*100)
next_time = time.time()

def oneround():
    try:
        s.send(message)
        data = s.recv(1500)
        status = self.clientstatus
        if status == '1':
            next_time += delay
            sch.enterabs(next_time, 0, oneround, ())
    except:
        pass

sch.enterabs(next_time, 0, oneround, ())

sch.run()

This will stay as close to one event every 1.0 / (speed*100) seconds as feasible -- if one event was delayed (we're not in a real hard time environment so the operating system can cause unpredictable delays) the next one will be scheduled nearer in the future, &c. The implied loop ends when nothing more is entered in sch.

answered Feb 1, 2015 at 3:27

Alex Martelli

887k175 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Nyoa Over a year ago

I'd like to test this but I have to create the socket outside the function oneround(). That means I'd need to pass socket, delay and message as arguments and then wouldn't be able to call the function again with sch.enterabs(). Is there a way around this (like making the arguments class wide) or should I make the server in oneround()?

Nyoa Over a year ago

Your suggestion worked perfectly after I got it right. Thank you alot. I'll add the working code here

Collectives™ on Stack Overflow

How to make while loop in python that is reliable enough for packet generator

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related