【优化tornado阻塞任务的三个选择】
1、优化阻塞的任务，使其执行时间更快。经常由于是一个DB的慢查询，或者复杂的上层模板导致的，这个时候首要的是加速这些任务，而不是优化复杂的webserver。可以提升99%的效率。
2、开启一个单独的线程或者进程执行耗时任务。这意味着对于IOLoop来说，可以开启另一个线程（或进程）处理off-loading任务，这样它就可以再接收其他请求了，而不是阻塞住。
3、使用异步的驱动或者库函数来执行任务，例如gevent , motor。
【例子1】
import time
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world %s" % time.time())
class SleepHandler(tornado.web.RequestHandler):
def get(self, n):
time.sleep(float(n))
self.write("Awake! %s" % time.time())
application = tornado.web.Application([
(r"/", MainHandler),
(r"/sleep/(d+)", SleepHandler),
])
if __name__ == "__main__":
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()
这样在一个tab页中开启http://localhost:8888/sleep/10，同时在另一个tab页访问http://localhost:8888/，会发现没有打印"Hello World"直到第一个页面完成为止。实际上，第一个调用将IOLoop阻塞住了，导致其无法响应第二个请求。
【例子2——非阻塞模式】
from concurrent.futures import ThreadPoolExecutor
from functools import partial, wraps
import tornado.ioloop
import tornado.web
EXECUTOR = ThreadPoolExecutor(max_workers=4)
def unblock(f):
@tornado.web.asynchronous
@wraps(f)
def wrapper(*args, **kwargs):
self = args[0]
def callback(future):
self.write(future.result())
self.finish()
EXECUTOR.submit(
partial(f, *args, **kwargs)
).add_done_callback(
lambda future: tornado.ioloop.IOLoop.instance().add_callback(
partial(callback, future)))
return wrapper
class SleepHandler(tornado.web.RequestHandler):
@unblock
def get(self, n):
time.sleep(float(n))
return "Awake! %s" % time.time()
unblock修饰器将被修饰函数提交给线程池，返回一个future。在future中添加一个callback函数，并将控制权交给IOLoop。
这个回调函数最终将调用self.finish，并结束此次请求。
Note：这个修饰器函数本身还需要被tornado.web.asynchronous修饰，为了是避免调用self.finish太快。
self.write不是线程安全（thread-safe）的，因此避免在主线程中处理future的结果。
当你使用@tornado.web.asynchonous装饰器时，Tornado永远不会自己关闭连接，需要显式的self.finish()关闭
【完整的demo】
from concurrent.futures import ThreadPoolExecutor
from functools import partial, wraps
import time
import tornado.ioloop
import tornado.web
EXECUTOR = ThreadPoolExecutor(max_workers=4)
def unblock(f):
@tornado.web.asynchronous
@wraps(f)
def wrapper(*args, **kwargs):
self = args[0]
def callback(future):
self.write(future.result())
self.finish()
EXECUTOR.submit(
partial(f, *args, **kwargs)
).add_done_callback(
lambda future: tornado.ioloop.IOLoop.instance().add_callback(
partial(callback, future)))
return wrapper
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world %s" % time.time())
class SleepHandler(tornado.web.RequestHandler):
@unblock
def get(self, n):
time.sleep(float(n))
return "Awake! %s" % time.time()
class SleepAsyncHandler(tornado.web.RequestHandler):
@tornado.web.asynchronous
def get(self, n):
def callback(future):
self.write(future.result())
self.finish()
EXECUTOR.submit(
partial(self.get_, n)
).add_done_callback(
lambda future: tornado.ioloop.IOLoop.instance().add_callback(
partial(callback, future)))
def get_(self, n):
time.sleep(float(n))
return "Awake! %s" % time.time()
application = tornado.web.Application([
(r"/", MainHandler),
(r"/sleep/(d+)", SleepHandler),
(r"/sleep_async/(d+)", SleepAsyncHandler),
])
if __name__ == "__main__":
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()
【ThreadPoolExecutor】
上面涉及到ThreadPoolExecutor两个方法，初始化以及submit，查看帮助
class ThreadPoolExecutor(concurrent.futures._base.Executor) | Method resolution order: | ThreadPoolExecutor | concurrent.futures._base.Executor | __builtin__.object | | Methods defined here: | | __init__(self, max_workers) | Initializes a new ThreadPoolExecutor instance. | | Args: | max_workers: The maximum number of threads that can be used to | execute the given calls. | | submit(self, fn, *args, **kwargs) | Submits a callable to be executed with the given arguments. | | Schedules the callable to be executed as fn(*args, **kwargs) and returns | a Future instance representing the execution of the callable. | | Returns: | A Future representing the given call.
1、max_workers可以处理给定calls的最大线程数目，如果超过这个数目会怎么样呢？？
2、submit调用fn(*args, **kwargs),返回一个Future的实例
【Future】
Help on class Future in module concurrent.futures._base: class Future(__builtin__.object) | Represents the result of an asynchronous computation. | | Methods defined here: | | __init__(self) | Initializes the future. Should not be called by clients. | | __repr__(self) | | add_done_callback(self, fn) | Attaches a callable that will be called when the future finishes. | | Args: | fn: A callable that will be called with this future as its only | argument when the future completes or is cancelled. The callable | will always be called by a thread in the same process in which | it was added. If the future has already completed or been | cancelled then the callable will be called immediately. These | callables are called in the order that they were added.