Multi threading in python using parallel threads

Question

I created two threads each running different functions. What i tryed to achieve is if first thread ends then the second should also end ( i tryed achieving it using global variable) Once both the threads end the same procedure should continue. The script is not working as expected.

I am using Linux - Centos and python 2.7

#!/usr/bin/python
import threading
import time
import subprocess
import datetime
import os
import thread
command= "strace -o /root/Desktop/a.txt -c ./server"
final_dir = "/root/Desktop/"
exitflag = 0
# Define a function for the thread
def print_time(*args):
 os.chdir(final_dir)
 print "IN first thread"
 proc = subprocess.Popen(command,shell=True,stdout=subprocess.PIPE, stderr=subprocess.PIPE)
 proc.wait(70)
 exitflag=1
def print_time1(*args):
 print "In second thread"
 global exitflag
 while exitflag:
 thread.exit()
 #proc = subprocess.Popen(command1,shell=True,stdout=subprocess.PIPE, sterr=subprocess.PIPE)
# Create two threads as follows
 while (1):
 t1=threading.Thread(target=print_time)
 t1.start()
 t2=threading.Thread(target=print_time1)
 t2=start()
 time.sleep(80)
 z = t1.isAlive()
 z1 = t2.isAlive()
 if z:
 z.exit()
 if z1:
 z1.exit()
 threading.Thread(target=print_time1).start()
 threading.Thread(target=print_time1).start()
 print "In try"

Where am i going wrong?

Answer 1

You could create an object to share state, and have the dependent thread check that state. Something like:

import threading
import time
import datetime
class Worker1( threading.Thread ):
 def __init__(self, state):
 super(Worker1, self).__init__()
 self.state = state 
 def run(self):
 print_time_helper("Worker1 Start")
 time.sleep(4)
 print_time_helper("Worker1 End")
 self.state.keepOnRunning = False
class Worker2( threading.Thread ):
 def __init__(self, state):
 super(Worker2, self).__init__()
 self.state = state 
 def run(self):
 while self.state.keepOnRunning:
 print_time_helper("Worker2")
 time.sleep(1)
class State( object ):
 def __init__(self):
 self.keepOnRunning = True 
def main():
 state = State()
 thread1 = Worker1(state)
 thread2 = Worker2(state)
 thread1.start()
 thread2.start()
 thread1.join()
 thread2.join()
def print_time_helper(name):
 print "{0}: {1}".format(name, datetime.datetime.now().time().strftime("%S"))

which will output something like this (numbers show current time seconds):

Worker1 Start: 39
Worker2: 39
Worker2: 40
Worker2: 41
Worker2: 42
Worker1 End: 43

However, this is a bit simplistic for most situations. You might be better off using message queues - this is a good intro.

• user2087340: it directly gives me Worker1 End: 25

Answer 2

Use a threading.Event instead of an int and wait for it to be set.

Also your logic appears to be wrong in print_time1 because your while loop will never run since exitflag is initially 0, but even if it was 1 it would still just exit immediately. It's not actually waiting on anything.