python Asyncore.dispatcher 理解

晓山青青

1、Asyncore是python的标准库。Asyncore.dispatcher 是这个库中的一个socket的框架，为socket添加了一些通用的回调方法，比如：

def listen(self, num):

def bind(self, addr):

def connect(self, address):

def accept(self):

def send(self, data):

def recv(self, buffer_size):

def close(self):
def handle_read(self):
self.log_info('unhandled read event', 'warning')
def handle_write(self):
self.log_info('unhandled write event', 'warning')
def handle_connect(self):
self.log_info('unhandled connect event', 'warning')
def handle_accept(self):
self.log_info('unhandled accept event', 'warning')
def handle_close(self):
self.log_info('unhandled close event', 'warning')
self.close()

　　

　　2、Asyncore.dispatcher 对socket进行了一次封装之后，这个socket就可以添加到一个全局的字典中，Asyncore模块中的loop函数会对这些socket文件描述符进行监视，具体可能是select或者poll方法实现，windows上面是poll实现的。通过I/O多路复用实现同时处理多个请求，避免使用多线程或者多进程的方式。下面中loop中传入的map就是socket-dispatcher的对象集合，当发现对应的socket有可读可写的请求时，调用对应的handle_read 和handle_write方法。

def poll(timeout=0.0, map=None):
if map is None:
map = socket_map
if map:
r = []; w = []; e = []
for fd, obj in map.items():
is_r = obj.readable()
is_w = obj.writable()
if is_r:
r.append(fd)
# accepting sockets should not be writable
if is_w and not obj.accepting:
w.append(fd)
if is_r or is_w:
e.append(fd)
if [] == r == w == e:
time.sleep(timeout)
return
try:
r, w, e = select.select(r, w, e, timeout)
except select.error, err:
if err.args[0] != EINTR:
raise
else:
return
for fd in r:
obj = map.get(fd)
if obj is None:
continue
read(obj)
for fd in w:
obj = map.get(fd)
if obj is None:
continue
write(obj)
for fd in e:
obj = map.get(fd)
if obj is None:
continue
_exception(obj)
def poll2(timeout=0.0, map=None):
# Use the poll() support added to the select module in Python 2.0
if map is None:
map = socket_map
if timeout is not None:
# timeout is in milliseconds
timeout = int(timeout*1000)
pollster = select.poll()
if map:
for fd, obj in map.items():
flags = 0
if obj.readable():
flags |= select.POLLIN | select.POLLPRI
# accepting sockets should not be writable
if obj.writable() and not obj.accepting:
flags |= select.POLLOUT
if flags:
# Only check for exceptions if object was either readable
# or writable.
flags |= select.POLLERR | select.POLLHUP | select.POLLNVAL
pollster.register(fd, flags)
try:
r = pollster.poll(timeout)
except select.error, err:
if err.args[0] != EINTR:
raise
r = []
for fd, flags in r:
obj = map.get(fd)
if obj is None:
continue
readwrite(obj, flags)
poll3 = poll2                           # Alias for backward compatibility
def loop(timeout=30.0, use_poll=False, map=None, count=None):
if map is None:
map = socket_map
if use_poll and hasattr(select, 'poll'):
poll_fun = poll2
else:
poll_fun = poll
if count is None:
while map:
poll_fun(timeout, map)
else:
while map and count > 0:
poll_fun(timeout, map)
count = count – 1　　

　　3、如何实现一个异步的服务器，官方给出了一个比较好的代码：

import logging
import asyncore
import socket
logging.basicConfig(level=logging.DEBUG, format="%(created)-15s %(msecs)d %(levelname)8s %(thread)d %(name)s %(message)s")
log                     = logging.getLogger(__name__)
BACKLOG                 = 5
SIZE                    = 1024
class EchoHandler(asyncore.dispatcher):
def __init__(self, conn_sock, client_address, server):
self.server             = server
self.client_address     = client_address
self.buffer             = ""
# We dont have anything to write, to start with
self.is_writable        = False
# Create ourselves, but with an already provided socket
asyncore.dispatcher.__init__(self, conn_sock)
log.debug("created handler; waiting for loop")
def readable(self):
return True     # We are always happy to read
def writable(self):
return self.is_writable # But we might not have
# anything to send all the time
def handle_read(self):
log.debug("handle_read")
data = self.recv(SIZE)
log.debug("after recv")
if data:
log.debug("got data")
self.buffer += data
self.is_writable = True  # sth to send back now
else:
log.debug("got null data")
def handle_write(self):
log.debug("handle_write")
if self.buffer:
sent = self.send(self.buffer)
log.debug("sent data")
self.buffer = self.buffer[sent:]
else:
log.debug("nothing to send")
if len(self.buffer) == 0:
self.is_writable = False
# Will this ever get called?  Does loop() call
# handle_close() if we called close, to start with?
def handle_close(self):
log.debug("handle_close")
log.info("conn_closed: client_address=%s:%s" % \
(self.client_address[0],
self.client_address[1]))
self.close()
#pass
class EchoServer(asyncore.dispatcher):
allow_reuse_address         = False
request_queue_size          = 5
address_family              = socket.AF_INET
socket_type                 = socket.SOCK_STREAM
def __init__(self, address, handlerClass=EchoHandler):
self.address            = address
self.handlerClass       = handlerClass
asyncore.dispatcher.__init__(self)
self.create_socket(self.address_family,
self.socket_type)
if self.allow_reuse_address:
self.set_reuse_addr()
self.server_bind()
self.server_activate()
def server_bind(self):
self.bind(self.address)
log.debug("bind: address=%s:%s" % (self.address[0], self.address[1]))
def server_activate(self):
self.listen(self.request_queue_size)
log.debug("listen: backlog=%d" % self.request_queue_size)
def fileno(self):
return self.socket.fileno()
def serve_forever(self):
asyncore.loop()
# TODO: try to implement handle_request()
# Internal use
def handle_accept(self):
(conn_sock, client_address) = self.accept()
if self.verify_request(conn_sock, client_address):
self.process_request(conn_sock, client_address)
def verify_request(self, conn_sock, client_address):
return True
def process_request(self, conn_sock, client_address):
log.info("conn_made: client_address=%s:%s" % \
(client_address[0],
client_address[1]))
self.handlerClass(conn_sock, client_address, self)
def handle_close(self):
self.close()　　
　　使用示例：


interface = "0.0.0.0"
port = 8080
server = asyncore_echo_server.EchoServer((interface, port))
server.serve_forever()　　
　　代码中创建了两个dispatcher的子类，一个是server专门用于接受客户端的请求；一个是EchoHandler，用于收到请求的时候处理客户端的每一个请求。

　　
　　3、Asyncore.dispatcher 子类中的server和普通的Handler有什么区别？

　　区别只有一个地方，dispatcher初始化的时候，server会先创建一个socket，binding本地的地址和端口，然后listening，在listening的过程中会执行下列代码


def listen(self, num):
self.accepting = True
if os.name == 'nt' and num > 5:
num = 5
return self.socket.listen(num)

　　当self.accepting = True 之后，客户端所有的请求会当成accept处理，也就是收到一个请求，得到一个socket。如果这个时候不把这个socket传给handler，那么这个socket因为没有人保存会立即释放，导致socket关闭。