I am trying to use The Queue in python which will be multithreaded. I just wanted to know the approach I am using is correct or not. And if I am doing something redundant or If there is a better approach that I should use.
I am trying to get new requests from a table and schedule them using some logic to perform some operation like running a query.
So here from the main thread I spawn a separate thread for the queue.
if __name__=='__main__':
request_queue = SetQueue(maxsize=-1)
worker = Thread(target=request_queue.process_queue)
worker.setDaemon(True)
worker.start()
while True:
try:
#Connect to the database get all the new requests to be verified
db = Database(username_testschema, password_testschema, mother_host_testschema, mother_port_testschema, mother_sid_testschema, 0)
#Get new requests for verification
verify_these = db.query("SELECT JOB_ID FROM %s.table WHERE JOB_STATUS='%s' ORDER BY JOB_ID" %
(username_testschema, 'INITIATED'))
#If there are some requests to be verified, put them in the queue.
if len(verify_these) > 0:
for row in verify_these:
print "verifying : %s" % row[0]
verify_id = row[0]
request_queue.put(verify_id)
except Exception as e:
logger.exception(e)
finally:
time.sleep(10)
Now in the Setqueue class I have a process_queue function which is used for processing the top 2 requests in every run that were added to the queue.
'''
Overridding the Queue class to use set as all_items instead of list to ensure unique items added and processed all the time,
'''
class SetQueue(Queue.Queue):
def _init(self, maxsize):
Queue.Queue._init(self, maxsize)
self.all_items = set()
def _put(self, item):
if item not in self.all_items:
Queue.Queue._put(self, item)
self.all_items.add(item)
'''
The Multi threaded queue for verification process. Take the top two items, verifies them in a separate thread and sleeps for 10 sec.
This way max two requests per run will be processed.
'''
def process_queue(self):
while True:
scheduler_obj = Scheduler()
try:
if self.qsize() > 0:
for i in range(2):
job_id = self.get()
t = Thread(target=scheduler_obj.verify_func, args=(job_id,))
t.start()
for i in range(2):
t.join(timeout=1)
self.task_done()
except Exception as e:
logger.exception(
"QUEUE EXCEPTION : Exception occured while processing requests in the VERIFICATION QUEUE")
finally:
time.sleep(10)
I want to see if my understanding is correct and if there can be any issues with it.
So the main thread running in while True in the main func connects to database gets new requests and puts it in the queue. The worker thread(daemon) for the queue keeps on getting new requests from the queue and fork non-daemon threads which do the processing and since timeout for the join is 1 the worker thread will keep on taking new requests without getting blocked, and its child thread will keep on processing in the background. Correct?
So in case if the main process exit these won`t be killed until they finish their work but the worker daemon thread would exit. Doubt : If the parent is daemon and child is non daemon and if parent exits does child exit?).
I also read here :- David beazley multiprocessing
By david beazley in using a Pool as a Thread Coprocessor section where he is trying to solve a similar problem. So should I follow his steps :- 1. Create a pool of processes. 2. Open a thread like I am doing for request_queue 3. In that thread
def process_verification_queue(self):
while True:
try:
if self.qsize() > 0:
job_id = self.get()
pool.apply_async(Scheduler.verify_func, args=(job_id,))
except Exception as e:
logger.exception("QUEUE EXCEPTION : Exception occured while processing requests in the VERIFICATION QUEUE")
Use a process from the pool and run the verify_func in parallel. Will this give me more performance?
