I would like to ask how tornado.concurrent.run_on_executor (later just run_on_executor
) works, because
I probably do not understand how to run synchronous task to not block the main IOLoop.
All the examples using run_on_executor
, which I found, are using just time
to block the loop.
With time
module it works fine, but when I try some time intesive calculations, using run_on_executor
, the task blocks the IOLoop.
I am able to see that the app uses multiple threads, but it is still blocking.
I want to use run_on_executor
for hashing passwords using bcrypt
, but replaced it with this calculation to gain some extra time for testing.
Here I have small app, to demonstrate my confusion.
from tornado.options import define, options
import tornado.web
import tornado.httpserver
from tornado import gen
from tornado.concurrent import run_on_executor
import tornado.httpclient
import tornado.escape
import time
import concurrent.futures
import urllib
executor = concurrent.futures.ThreadPoolExecutor(20)
define("port", default=8888, help="run on the given port", type=int)
# Should not be blocking ?
class ExpHandler(tornado.web.RequestHandler):
_thread_pool = executor
@gen.coroutine
def get(self, num):
i = int(num)
result = yield self.exp(2, i)
self.write(str(result))
self.finish()
@run_on_executor(executor="_thread_pool")
def exp(self, x, y):
result = x ** y
return(result)
class NonblockingHandler(tornado.web.RequestHandler):
@gen.coroutine
def get(self):
http_client = tornado.httpclient.AsyncHTTPClient()
try:
response = yield http_client.fetch("http://www.google.com/")
self.write(response.body)
except tornado.httpclient.HTTPError as e:
self.write(("Error: " + str(e)))
finally:
http_client.close()
self.finish()
class SleepHandler(tornado.web.RequestHandler):
_thread_pool = executor
@gen.coroutine
def get(self, sec):
sec = float(sec)
start = time.time()
res = yield self.sleep(sec)
self.write("Sleeped for {} s".format((time.time() - start)))
self.finish()
@run_on_executor(executor="_thread_pool")
def sleep(self, sec):
time.sleep(sec)
return(sec)
class Application(tornado.web.Application):
def __init__(self):
handlers = [
(r'/exp/(?P<num>[^\/]+)?', ExpHandler),
(r'/nonblocking/?', NonblockingHandler),
(r'/sleep/(?P<sec>[^\/]+)?',SleepHandler)
]
settings = dict(
debug=True,
logging="debug"
)
tornado.web.Application.__init__(self, handlers, **settings)
def main():
tornado.options.parse_command_line()
http_server = tornado.httpserver.HTTPServer(Application())
http_server.listen(options.port)
io_loop = tornado.ioloop.IOLoop.instance()
io_loop.start()
if __name__ == "__main__":
main()
I would be very grateful for any explanation why ExpHandler
, running in executor
is blocking the loop.
Python (at least in the CPython implementation) has a Global Interpreter Lock which prevents multiple threads from executing Python code at the same time. In particular, anything which runs in a single Python opcode is uninterruptible unless it calls a C function which explicitly releases the GIL. A large exponentation with
**
holds the GIL the whole time and thus blocks all other python threads, while a call tobcrypt()
will release the GIL so other threads can continue to work.