import subprocess,threading,fcntl,os,time
end_time = time.time()+5
lock = threading.Lock()
use_lock = False
path_to_factorial = os.path.join(os.path.dirname(os.path.realpath(__file__)),'factorial.sh')

def testFunction():
    print threading.current_thread().name,'| pre-Popen'
    if use_lock: lock.acquire()
    p = subprocess.Popen([path_to_factorial],stdin=subprocess.PIPE,stdout=subprocess.PIPE,stderr=subprocess.PIPE)
    if use_lock: lock.release()
    print threading.current_thread().name,'| post-Popen'
    fcntl.fcntl(p.stdout,fcntl.F_SETFL,os.O_NONBLOCK)
    fcntl.fcntl(p.stderr,os.O_NONBLOCK)
    while time.time()<end_time:
        try: p.stdout.read()
        except: pass
        try: p.stderr.read()
        except: pass
    print threading.current_thread().name,'| DONE'

for i in range(3):
    threading.Thread(target=testFunction).start()

#!/bin/sh
echo "Calculating factorial (anything that's somewhat compute intensive,this script takes 3 sec on my machine"
ans=1
counter=0
fact=999
while [ $fact -ne $counter ]
do
    counter=`expr $counter + 1`
    ans=`expr $ans \* $counter`
done
echo "Factorial calculation done"
read -p "Test input (this part is critical for bug to occur): " buf
echo "$buf"