I have a python program that implements threads like this:
class Mythread(threading.Thread):
def __init__(self, name, q):
threading.Thread.__init__(self)
self.name = name
self.q = q
def run(self):
print "Starting %s..." % (self.name)
while True:
## Get data from queue
data = self.q.get()
## do_some_processing with data ###
process_data(data)
## Mark Queue item as done
self.q.task_done()
print "Exiting %s..." % (self.name)
def call_threaded_program():
##Setup the threads. Define threads,queue,locks
threads = []
q = Queue.Queue()
thread_count = n #some number
data_list = [] #some data list containing data
##Create Threads
for thread_id in range(1, thread_count+1):
thread_name = "Thread-" + str(thread_id)
thread = Mythread(thread_name,q)
thread.daemon = True
thread.start()
##Fill data in Queue
for data_item in data_list:
q.put(data_item)
try:
##Wait for queue to be exhausted and then exit main program
q.join()
except (KeyboardInterrupt, SystemExit) as e:
print "Interrupt Issued. Exiting Program with error state: %s"%(str(e))
exit(1)
The call_threaded_program() is called from a different program.
I have the code working under normal circumstances. However if an error/exception occurs in one of the threads, then the program is stuck (as the queue join is infinitely blocking). The only way I am able to quit this program is to close the terminal itself.
What is the best way to terminate this program when a thread bails out? Is there a clean (actually I would take any way) way of doing this? I know this question has been asked numerous times, but I am still unable to find a convincing answer. I would really appreciate any help.
EDIT: I tried removing the join on the queue and used a global exit flag as suggested in Is there any way to kill a Thread in Python? However, Now the behavior is so strange, I can't comprehend what is going on.
import threading
import Queue
import time
exit_flag = False
class Mythread (threading.Thread):
def __init__(self,name,q):
threading.Thread.__init__(self)
self.name = name
self.q = q
def run(self):
try:
# Start Thread
print "Starting %s...."%(self.name)
# Do Some Processing
while not exit_flag:
data = self.q.get()
print "%s processing %s"%(self.name,str(data))
self.q.task_done()
# Exit thread
print "Exiting %s..."%(self.name)
except Exception as e:
print "Exiting %s due to Error: %s"%(self.name,str(e))
def main():
global exit_flag
##Setup the threads. Define threads,queue,locks
threads = []
q = Queue.Queue()
thread_count = 20
data_list = range(1,50)
##Create Threads
for thread_id in range(1,thread_count+1):
thread_name = "Thread-" + str(thread_id)
thread = Mythread(thread_name,q)
thread.daemon = True
threads.append(thread)
thread.start()
##Fill data in Queue
for data_item in data_list:
q.put(data_item)
try:
##Wait for queue to be exhausted and then exit main program
while not q.empty():
pass
# Stop the threads
exit_flag = True
# Wait for threads to finish
print "Waiting for threads to finish..."
while threading.activeCount() > 1:
print "Active Threads:",threading.activeCount()
time.sleep(1)
pass
print "Finished Successfully"
except (KeyboardInterrupt, SystemExit) as e:
print "Interrupt Issued. Exiting Program with error state: %s"%(str(e))
if __name__ == '__main__':
main()
The program's output is as below:
#Threads get started correctly
#The output also is getting processed but then towards the end, All i see are
Active Threads: 16
Active Threads: 16
Active Threads: 16...
The program then just hangs or keeps on printing the active threads. However since the exit flag is set to True, the thread's run method is not being exercised. So I have no clue as to how these threads are kept up or what is happening.
EDIT: I found the problem. In the above code, thread's get method were blocking and hence unable to quit. Using a get method with a timeout instead did the trick. I have the code for just the run method that I modified below
def run(self):
try:
#Start Thread
printing "Starting %s..."%(self.name)
#Do Some processing
while not exit_flag:
try:
data = self.q.get(True,self.timeout)
print "%s processing %s"%(self.name,str(data))
self.q.task_done()
except:
print "Queue Empty or Timeout Occurred. Try Again for %s"%(self.name)
# Exit thread
print "Exiting %s..."%(self.name)
except Exception as e:
print "Exiting %s due to Error: %s"%(self.name,str(e))
