asyncore — 异步套接字处理程序

源代码: Lib/asyncore.py

从 3.6 版起弃用: 请使用 asyncio 代替。


注意

此模块的存在只为向后兼容。对于新的代码,推荐使用 asyncio .

此模块为编写异步套接字服务客户端和服务器提供基本的基础设施。

There are only two ways to have a program on a single processor do “more than one thing at a time.” Multi-threaded programming is the simplest and most popular way to do it, but there is another very different technique, that lets you have nearly all the advantages of multi-threading, without actually using multiple threads. It’s really only practical if your program is largely I/O bound. If your program is processor bound, then pre-emptive scheduled threads are probably what you really need. Network servers are rarely processor bound, however.

若操作系统支持 select() system call in its I/O library (and nearly all do), then you can use it to juggle multiple communication channels at once; doing other work while your I/O is taking place in the “background.” Although this strategy can seem strange and complex, especially at first, it is in many ways easier to understand and control than multi-threaded programming. The asyncore module solves many of the difficult problems for you, making the task of building sophisticated high-performance network servers and clients a snap. For “conversational” applications and protocols the companion asynchat module is invaluable.

The basic idea behind both modules is to create one or more network channels , instances of class asyncore.dispatcher and asynchat.async_chat . Creating the channels adds them to a global map, used by the loop() function if you do not provide it with your own map .

一旦创建初始通道,就会调用 loop() function activates channel service, which continues until the last channel (including any that have been added to the map during asynchronous service) is closed.

asyncore. loop ( [ timeout [ , use_poll [ , map [ , count ] ] ] ] )

Enter a polling loop that terminates after count passes or all open channels have been closed. All arguments are optional. The count parameter defaults to None , resulting in the loop terminating only when all channels have been closed. The timeout argument sets the timeout parameter for the appropriate select() or poll() call, measured in seconds; the default is 30 seconds. The use_poll parameter, if true, indicates that poll() should be used in preference to select() (the default is False ).

map parameter is a dictionary whose items are the channels to watch. As channels are closed they are deleted from their map. If map is omitted, a global map is used. Channels (instances of asyncore.dispatcher , asynchat.async_chat and subclasses thereof) can freely be mixed in the map.

class asyncore. dispatcher

dispatcher 类是围绕低级套接字对象的瘦包裹器。为使它变得更有用,它带有一些从异步循环调用的事件处理方法。否则,它可以被视为正常非阻塞套接字对象。

The firing of low-level events at certain times or in certain connection states tells the asynchronous loop that certain higher-level events have taken place. For example, if we have asked for a socket to connect to another host, we know that the connection has been made when the socket becomes writable for the first time (at this point you know that you may write to it with the expectation of success). The implied higher-level events are:

事件

描述

handle_connect()

Implied by the first read or write event

handle_close()

Implied by a read event with no data available

handle_accepted()

Implied by a read event on a listening socket

在异步处理期间,每个映射通道的 readable() and writable() methods are used to determine whether the channel’s socket should be added to the list of channels select() ed or poll() ed for read and write events.

Thus, the set of channel events is larger than the basic socket events. The full set of methods that can be overridden in your subclass follows:

handle_read ( )

被调用当异步循环检测到 read() 调用在通道的套接字中会成功。

handle_write ( )

Called when the asynchronous loop detects that a writable socket can be written. Often this method will implement the necessary buffering for performance. For example:

def handle_write(self):
    sent = self.send(self.buffer)
    self.buffer = self.buffer[sent:]
											
handle_expt ( )

Called when there is out of band (OOB) data for a socket connection. This will almost never happen, as OOB is tenuously supported and rarely used.

handle_connect ( )

Called when the active opener’s socket actually makes a connection. Might send a “welcome” banner, or initiate a protocol negotiation with the remote endpoint, for example.

handle_close ( )

被调用当套接字关闭时。

handle_error ( )

Called when an exception is raised and not otherwise handled. The default version prints a condensed traceback.

handle_accept ( )

Called on listening channels (passive openers) when a connection can be established with a new remote endpoint that has issued a connect() call for the local endpoint. Deprecated in version 3.2; use handle_accepted() 代替。

从 3.2 版起弃用。

handle_accepted ( sock , addr )

Called on listening channels (passive openers) when a connection has been established with a new remote endpoint that has issued a connect() call for the local endpoint. sock new 套接字对象用于发送和接收数据当连接上时,和 addr 是绑定到连接另一端的套接字地址。

3.2 版新增。

readable ( )

Called each time around the asynchronous loop to determine whether a channel’s socket should be added to the list on which read events can occur. The default method simply returns True , indicating that by default, all channels will be interested in read events.

writable ( )

Called each time around the asynchronous loop to determine whether a channel’s socket should be added to the list on which write events can occur. The default method simply returns True , indicating that by default, all channels will be interested in write events.

In addition, each channel delegates or extends many of the socket methods. Most of these are nearly identical to their socket partners.

create_socket ( family=socket.AF_INET , type=socket.SOCK_STREAM )

This is identical to the creation of a normal socket, and will use the same options for creation. Refer to the socket documentation for information on creating sockets.

3.3 版改变: 系列 and type 自变量可以省略。

connect ( address )

As with the normal socket object, address is a tuple with the first element the host to connect to, and the second the port number.

send ( data )

发送 data to the remote end-point of the socket.

recv ( buffer_size )

读取最多 buffer_size bytes from the socket’s remote end-point. An empty bytes object implies that the channel has been closed from the other end.

注意, recv() 可能引发 BlockingIOError , even though select.select() or select.poll() has reported the socket ready for reading.

listen ( backlog )

监听套接字建立的连接。 backlog argument specifies the maximum number of queued connections and should be at least 1; the maximum value is system-dependent (usually 5).

bind ( address )

将套接字绑定到 address 。套接字必须尚未绑定。(格式对于 address depends on the address family — refer to the socket documentation for more information.) To mark the socket as re-usable (setting the SO_REUSEADDR 选项),调用 dispatcher 对象的 set_reuse_addr() 方法。

accept ( )

Accept a connection. The socket must be bound to an address and listening for connections. The return value can be either None or a pair (conn, address) where conn new 套接字对象用于发送和接收数据当连接上时,和 address is the address bound to the socket on the other end of the connection. When None is returned it means the connection didn’t take place, in which case the server should just ignore this event and keep listening for further incoming connections.

close ( )

Close the socket. All future operations on the socket object will fail. The remote end-point will receive no more data (after queued data is flushed). Sockets are automatically closed when they are garbage-collected.

class asyncore. dispatcher_with_send

A dispatcher subclass which adds simple buffered output capability, useful for simple clients. For more sophisticated usage use asynchat.async_chat .

class asyncore. file_dispatcher

file_dispatcher 接受文件描述符或 文件对象 along with an optional map argument and wraps it for use with the poll() or loop() functions. If provided a file object or anything with a fileno() method, that method will be called and passed to the file_wrapper 构造函数。

可用性 : Unix.

class asyncore. file_wrapper

A file_wrapper takes an integer file descriptor and calls os.dup() to duplicate the handle so that the original handle may be closed independently of the file_wrapper. This class implements sufficient methods to emulate a socket for use by the file_dispatcher 类。

可用性 : Unix.

asyncore 范例基本 HTTP 客户端

这里是非常基本的 HTTP 客户端,使用 dispatcher 类来实现其套接字处理:

import asyncore
class HTTPClient(asyncore.dispatcher):
    def __init__(self, host, path):
        asyncore.dispatcher.__init__(self)
        self.create_socket()
        self.connect( (host, 80) )
        self.buffer = bytes('GET %s HTTP/1.0\r\nHost: %s\r\n\r\n' %
                            (path, host), 'ascii')
    def handle_connect(self):
        pass
    def handle_close(self):
        self.close()
    def handle_read(self):
        print(self.recv(8192))
    def writable(self):
        return (len(self.buffer) > 0)
    def handle_write(self):
        sent = self.send(self.buffer)
        self.buffer = self.buffer[sent:]
client = HTTPClient('www.python.org', '/')
asyncore.loop()
								

asyncore 范例基本回显服务器

这里是基本回显服务器使用 dispatcher 类接受连接并将传入连接分派给处理程序:

import asyncore
class EchoHandler(asyncore.dispatcher_with_send):
    def handle_read(self):
        data = self.recv(8192)
        if data:
            self.send(data)
class EchoServer(asyncore.dispatcher):
    def __init__(self, host, port):
        asyncore.dispatcher.__init__(self)
        self.create_socket()
        self.set_reuse_addr()
        self.bind((host, port))
        self.listen(5)
    def handle_accepted(self, sock, addr):
        print('Incoming connection from %s' % repr(addr))
        handler = EchoHandler(sock)
server = EchoServer('localhost', 8080)
asyncore.loop()