Question

我的问题简而言之：我不知道选择器如何知道哪个套接字应该首先读取或写入。

这是一台可以处理多个连接的服务器，其流应为：

服务器创建监听套接字
客户端创建2个套接字并将其连接到服务器
客户端2套接字发送消息
服务器2套接字回显这些消息，客户端和服务器关闭连接

会发生这种情况，但是如果创建的服务器套接字首先写入，则连接将立即关闭或抛出异常（？），因为它甚至不调用send且客户端套接字将不会接收任何内容。那么选择器如何知道哪些套接字应该首先准备好进行写/读呢？我想了解哪些信息？

服务器：

import socket
import selectors
import types

host = "127.0.0.1"
port = 63210

def accept_wrapper(sock):
    conn, addr = sock.accept()
    print('accepted connection from', addr)
    conn.setblocking(False)
    data = types.SimpleNamespace(addr=addr, inb=b'', outb=b'')
    events = selectors.EVENT_READ | selectors.EVENT_WRITE
    sel.register(conn, events, data=data)

def service_connection(key, mask):
    sock = key.fileobj
    data = key.data
    if mask & selectors.EVENT_READ:
        recv_data = sock.recv(1024)
        if recv_data:
            data.outb += recv_data
        else:
            print('closing connection to', data.addr)
            sel.unregister(sock)
            sock.close()
    if mask & selectors.EVENT_WRITE:
        if data.outb:
            print('echoing', repr(data.outb), 'to', data.addr)
            sent = sock.send(data.outb)
            data.outb = data.outb[sent:]

sel = selectors.DefaultSelector()

lsock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
lsock.bind((host, port))
lsock.listen()
print('listening on', (host, port))
lsock.setblocking(False)
sel.register(lsock, selectors.EVENT_READ, data=None)

while True:
    events = sel.select(timeout=None)
    for key, mask in events:
        if key.data is None:
            accept_wrapper(key.fileobj)
        else:
            service_connection(key, mask)

客户：

import socket
import selectors
import types

host = "127.0.0.1"
port = 63210
num_conns = 2
messages = [b'Message 1 from client.', b'Message 2 from client.']

def start_connections(host, port, num_conns):
    server_addr = (host, port)
    for i in range(0, num_conns):
        connid = i + 1
        print('starting connection', connid, 'to', server_addr)
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.setblocking(False)
        sock.connect_ex(server_addr)
        events = selectors.EVENT_READ | selectors.EVENT_WRITE
        data = types.SimpleNamespace(connid=connid,
                                     msg_total=sum(len(m) for m in messages),
                                     recv_total=0,
                                     messages=list(messages),
                                     outb=b'')
        sel.register(sock, events, data=data)

def service_connection(key, mask):
    sock = key.fileobj
    data = key.data
    if mask & selectors.EVENT_READ:
        recv_data = sock.recv(1024)
        if recv_data:
            print('received', repr(recv_data), 'from connection', data.connid)
            data.recv_total += len(recv_data)
        if not recv_data or data.recv_total == data.msg_total:
            print('closing connection', data.connid)
            sel.unregister(sock)
            sock.close()
    if mask & selectors.EVENT_WRITE:
        if not data.outb and data.messages:
            data.outb = data.messages.pop(0)
        if data.outb:
            print('sending', repr(data.outb), 'to connection', data.connid)
            sent = sock.send(data.outb)
            data.outb = data.outb[sent:]

sel = selectors.DefaultSelector()
start_connections(host, port, num_conns)

while True:
    events = sel.select(timeout=None)
    for key, mask in events:
        service_connection(key, mask)

Answer 1

我查看了您拥有的相同代码，并针对您所关心的问题提出了拉取请求： https://github.com/realpython/materials/pull/112

从本质上讲，答案是套接字和读写事件是系统在循环中循环的。最终，每个套接字都可以在此循环中进行读写，而您只需要等待转弯发生即可。

Answer 2

套接字实际上并不直接写到对等体，也不从对等体读取。相反，它们写入本地套接字特定的写缓冲区，并从套接字特定的读缓冲区读取。 OS内核关心将数据从套接字写缓冲区传递到对等方，并将从对等方接收到的数据包放入套接字接收缓冲区中。

可以使用诸如select，poll，kqueue之类的功能来监视这些内核套接字缓冲区的状态以及对这些缓冲区的更改。本质上：如果套接字写缓冲区中有空间，则认为该套接字可写。如果套接字读取缓冲区中有数据，则认为该套接字可读。

Python-使用选择器的非阻塞套接字

2 个答案: