对于我的Tornado服务器中预期阻塞的操作(并且不能轻易修改以使用Tornado的异步HTTP请求客户端之类的东西),我一直在使用多处理模块将工作卸载到单独的工作进程.具体来说,我使用的是一个多处理池,因为它提供了一个名为apply_async的方法,该方法与Tornado非常兼容,因为它将回调作为其参数之一.

我最近意识到池预先分配了进程数,因此如果它们都成为阻塞,那么需要新进程的操作将不得不等待.我确实意识到服务器仍然可以接受连接,因为apply_async通过向任务队列添加东西来工作,并且相当立即完成,但是我正在寻找为我需要执行的n个阻塞任务生成n个进程.

我想我可以为我的Tornado服务器的IOLoop使用add_handler方法为我为IOLoop创建的每个新PID添加一个处理程序.我之前做过类似的事情,但它使用的是popen和一个任意的命令.这种方法的使用示例是here.我想在我的范围内将参数传递给任意目标Python函数,所以我想坚持使用多处理.

但是,似乎有些东西不喜欢我的multiprocessing.Process对象所拥有的PID.我得到IOError：[Errno 9]错误的文件描述符.这些过程是否受到某种限制？我知道在实际启动过程之前PID不可用,但我确实开始了这个过程.这是我所做的一个示例的源代码,它演示了这个问题：

#!/usr/bin/env python

"""Creates a small Tornado program to demonstrate asynchronous programming.
Specifically, this demonstrates using the multiprocessing module."""

import tornado.httpserver
import tornado.ioloop
import tornado.web
import multiprocessing as mp
import random
import time

__author__ = 'Brian McFadden'
__email__ = 'brimcfadden@gmail.com'

def sleepy(queue):
    """Pushes a string to the queue after sleeping for 5 seconds.
    This sleeping can be thought of as a blocking operation."""

    time.sleep(5)
    queue.put("Now I'm awake.")
    return

def random_num():
    """Returns a string containing a random number.
    This function can be used by handlers to receive text for writing which
    facilitates noticing change on the webpage when it is refreshed."""

    n = random.random()
    return "<br />Here is a random number to show change: {0}".format(n)

class SyncHandler(tornado.web.RequestHandler):
    """Demonstrates handing a request synchronously.
    It executes sleepy() before writing some more text and a random number to
    the webpage. While the process is sleeping, the Tornado server cannot
    handle any requests at all."""

    def get(self):
        q = mp.Queue()
        sleepy(q)
        val = q.get()
        self.write(val)
        self.write('<br />Brought to you by SyncHandler.')
        self.write('<br />Try refreshing me and then the main page.')
        self.write(random_num())

class AsyncHandler(tornado.web.RequestHandler):
    """Demonstrates handing a request asynchronously.
    It executes sleepy() before writing some more text and a random number to
    the webpage. It passes the sleeping function off to another process using
    the multiprocessing module in order to handle more requests concurrently to
    the sleeping, which is like a blocking operation."""

    @tornado.web.asynchronous
    def get(self):
        """Handles the original GET request (normal function delegation).
        Instead of directly invoking sleepy(), it passes a reference to the
        function to the multiprocessing pool."""

        # Create an interprocess data structure, a queue.
        q = mp.Queue()
        # Create a process for the sleepy function. Provide the queue.
        p = mp.Process(target=sleepy, args=(q,))
        # Start it, but don't use p.join(); that would block us.
        p.start()
        # Add our callback function to the IOLoop. The async_callback wrapper
        # makes sure that Tornado sends an HTTP 500 error to the client if an
        # uncaught exception occurs in the callback.
        iol = tornado.ioloop.IOLoop.instance()
        print "p.pid:", p.pid
        iol.add_handler(p.pid, self.async_callback(self._finish, q), iol.READ)

    def _finish(self, q):
        """This is the callback for post-sleepy() request handling.
        Operation of this function occurs in the original process."""

        val = q.get()
        self.write(val)
        self.write('<br />Brought to you by AsyncHandler.')
        self.write('<br />Try refreshing me and then the main page.')
        self.write(random_num())
        # Asynchronous handling must be manually finished.
        self.finish()

class MainHandler(tornado.web.RequestHandler):
    """Returns a string and a random number.
    Try to access this page in one window immediately after (<5 seconds of)
    accessing /async or /sync in another window to see the difference between
    them. Asynchronously performing the sleepy() function won't make the client
    wait for data from this handler, but synchronously doing so will!"""

    def get(self):
        self.write('This is just responding to a simple request.')
        self.write('<br />Try refreshing me after one of the other pages.')
        self.write(random_num())

if __name__ == '__main__':
    # Create an application using the above handlers.
    application = tornado.web.Application([
        (r"/", MainHandler),
        (r"/sync", SyncHandler),
        (r"/async", AsyncHandler),
    ])
    # Create a single-process Tornado server from the application.
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(8888)
    print 'The HTTP server is listening on port 8888.'
    tornado.ioloop.IOLoop.instance().start()

这是追溯：

Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/tornado/web.py", line 810, in _stack_context
    yield
  File "/usr/local/lib/python2.6/dist-packages/tornado/stack_context.py", line 77, in StackContext
    yield
  File "/usr/local/lib/python2.6/dist-packages/tornado/web.py", line 827, in _execute
    getattr(self, self.request.method.lower())(*args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/tornado/web.py", line 909, in wrapper
    return method(self, *args, **kwargs)
  File "./process_async.py", line 73, in get
    iol.add_handler(p.pid, self.async_callback(self._finish, q), iol.READ)
  File "/usr/local/lib/python2.6/dist-packages/tornado/ioloop.py", line 151, in add_handler
    self._impl.register(fd, events | self.ERROR)
IOError: [Errno 9] Bad file descriptor

上面的代码实际上是从使用进程池的旧示例中修改的.我已经将它保存起来作为我的同事和我自己的参考(因此大量的评论)已经有一段时间了.我以这样的方式构建它,以便我可以并排打开两个小浏览器窗口向我的老板证明/ sync URI阻止连接,而/ async允许更多连接.出于此问题的目的,您需要做的只是尝试访问/ async处理程序.它立即出错.

我该怎么办？ PID怎么会“坏”？如果您运行该程序,您可以看到它打印到stdout.

为了记录,我在Ubuntu 10.04上使用Python 2.6.5.龙卷风是1.1.

解决方法:

add_handler采用有效的文件描述符,而不是PID.作为预期的一个例子,龙卷风本身通常通过传入套接字对象的fileno()来使用add_handler,它返回对象的文件描述符.在这种情况下,PID无关紧要.