前言：

     话说Tornado  是由Facebook开源的一个服务器“套装”,适合于做python的web或者使用其本身提供的可扩展的功能，完成了不完整的wsgi协议，可用于做快速的web开发，封装了epoll性能较好。文章主要以分析tornado的网络部分即异步事件处理与上层的IOstream类提供的异步IO，其他的模块如web的tornado.web 以后慢慢留作分析。

源码组织：

|---__init__.py

---auth.py

---......

---epoll.c

---ioloop.py

---iostream.py

---...

tornado网络部分最核心的两个模块就是ioloop.py与iostream.py，我们主要分析的就是这两个部分。

ioloop.py 主要的是将底层的epoll或者说是其他的IO多路复用封装作异步事件来处理

iostream.py主要是对于下层的异步事件的进一步封装，为其封装了更上一层的buffer（IO）事件.

扯了半天，没有说正题…  

前段时间一直在看tornado的代码，看起来有些晕，但是收获还是不小.   废话不多说。 最近有个应用场景是需要tornado subprocess组合的，具体的业务就不描述了，我所要的事情就是使用subprocess调用一个java的脚本..   又是java… 

有朋友说我抄袭subprocess代码,  我只是忘了贴源地址？ 好家伙居然成抄袭了…. 

https://github.com/vukasin/tornado-subprocess/blob/master/tornado_subprocess/__init__.py

import subprocess
import tornado.ioloop
import time
import fcntl
import functools
import os
class GenericSubprocess (object):
    def __init__ ( self, timeout=-1, **popen_args ):
        self.args = dict()
        self.args["stdout"] = subprocess.PIPE
        self.args["stderr"] = subprocess.PIPE
        self.args["close_fds"] = True
        self.args.update(popen_args)
        self.ioloop = None
        self.expiration = None
        self.pipe = None
        self.timeout = timeout
        self.streams = []
        self.has_timed_out = False
    def start(self):
        """Spawn the task.
        Throws RuntimeError if the task was already started."""
        if not self.pipe is None:
            raise RuntimeError("Cannot start task twice")
        self.ioloop = tornado.ioloop.IOLoop.instance()
        if self.timeout > 0:
            self.expiration = self.ioloop.add_timeout( time.time() + self.timeout, self.on_timeout )
        self.pipe = subprocess.Popen(**self.args)
        self.streams = [ (self.pipe.stdout.fileno(), []),
                             (self.pipe.stderr.fileno(), []) ]
        for fd, d in self.streams:
            flags = fcntl.fcntl(fd, fcntl.F_GETFL)| os.O_NDELAY
            fcntl.fcntl( fd, fcntl.F_SETFL, flags)
            self.ioloop.add_handler( fd,
                                     self.stat,
                                     self.ioloop.READ|self.ioloop.ERROR)
    def on_timeout(self):
        self.has_timed_out = True
        self.cancel()
    def cancel (self ) :
        """Cancel task execution
        Sends SIGKILL to the child process."""
        try:
            self.pipe.kill()
        except:
            pass
    def stat( self, *args ):
        '''Check process completion and consume pending I/O data'''
        self.pipe.poll()
        if not self.pipe.returncode is None:
            '''cleanup handlers and timeouts'''
            if not self.expiration is None:
                self.ioloop.remove_timeout(self.expiration)
            for fd, dest in  self.streams:
                self.ioloop.remove_handler(fd)
            '''schedulle callback (first try to read all pending data)'''
            self.ioloop.add_callback(self.on_finish)
        for fd, dest in  self.streams:
            while True:
                try:
                    data = os.read(fd, 4096)
                    if len(data) == 0:
                        break
                    dest.extend([data])
                except:
                    break
    @property
    def stdout(self):
        return self.get_output(0)
    @property
    def stderr(self):
        return self.get_output(1)
    @property
    def status(self):
        return self.pipe.returncode
    def get_output(self, index ):
        return "".join(self.streams[index][1])
    def on_finish(self):
        raise NotImplemented()
class Subprocess (GenericSubprocess):
    def __init__ ( self, callback, *args, **kwargs):
        self.callback = callback
        self.done_callback = False
        GenericSubprocess.__init__(self, *args, **kwargs)
    def on_finish(self):
        if not self.done_callback:
            self.done_callback = True
            '''prevent calling callback twice'''
            self.ioloop.add_callback(functools.partial(self.callback, self.status, self.stdout, self.stderr, self.has_timed_out))
if __name__ == "__main__":
    ioloop = tornado.ioloop.IOLoop.instance()
    def print_timeout( status, stdout, stderr, has_timed_out) :
        assert(status!=0)
        assert(has_timed_out)
        print "OK status:", repr(status), "stdout:", repr(stdout), "stderr:", repr(stderr), "timeout:", repr(has_timed_out)
    def print_ok( status, stdout, stderr, has_timed_out) :
        assert(status==0)
        assert(not has_timed_out)
        print "OK status:", repr(status), "stdout:", repr(stdout), "stderr:", repr(stderr), "timeout:", repr(has_timed_out)
    def print_error( status, stdout, stderr, has_timed_out):
        assert(status!=0)
        assert(not has_timed_out)
        print "OK status:", repr(status), "stdout:", repr(stdout), "stderr:", repr(stderr), "timeout:", repr(has_timed_out)
    def stop_test():
        ioloop.stop()
    t1 = Subprocess( print_timeout, timeout=3, args=[ "sleep","5"] )
    t2 = Subprocess( print_ok, timeout=3, args=[ "ip", "a" ] )
    t3 = Subprocess( print_ok, timeout=3, args=[ "sleepdsdasdas", "1" ] )
    t4 = Subprocess( print_error, timeout=3, args=[ "cat", "/etc/sdfsdfsdfsdfsdfsdfsdf" ] )
    t1.start()
    t2.start()
    try:
        t3.start()
        assert(false)
    except:
        print "OK"
    t4.start()
    ioloop.add_timeout(time.time() + 10, stop_test)
    ioloop.start()

Tornado subprocess组合，在web api系统调用本身是尴尬的事情，尽量需要避免这样的应用。 

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