Python Asyncio如何重用套接字

如何在asyncio中重用服务器的套接字？而不是为每个查询创建新连接

这是我的密码

async def lookup(server, port, query, sema):
    async with sema as sema:
        try:
            reader, writer = await asyncio.open_connection(server, port)
        except:
            return {}
        writer.write(query.encode("ISO-8859-1"))
        await writer.drain()
        data = b""
        while True:
            d = await reader.read(4096)
            if not d:
                break
            data += d
        writer.close()
        data = data.decode("ISO-8859-1")
        return data

---

您可以通过将读写器对存储到全局字典来创建连接缓存

# at top-level
connections = {}

然后在

lookup

中，将对

open\u connection

的调用替换为首先检查dict的代码：

if (server, port) in connections:
    reader, writer = connections[server, port]
else:
    reader, writer = await asyncio.open_connection(server, port)
    connections[server, port] = reader, writer

---

您只需调用

asyncio.open\u连接（服务器、端口）

coroutine一次，并继续使用读写器（当然，前提是服务器不只是在其一端关闭连接）

我将在一个单独的异步上下文管理器对象中为您的连接执行此操作，并使用来管理连接，这样您就可以为许多并发任务创建和重用套接字连接。通过使用（异步）上下文管理器，Python确保在代码完成时通知连接，以便将连接释放回池：

import asyncio
import contextlib

from collections import OrderedDict
from types import TracebackType
from typing import Any, List, Optional, Tuple, Type


try:  # Python 3.7
    base = contextlib.AbstractAsyncContextManager
except AttributeError:
    base = object  # type: ignore

Server = str
Port = int
Host = Tuple[Server, Port]


class ConnectionPool(base):
    def __init__(
        self,
        max_connections: int = 1000,
        loop: Optional[asyncio.AbstractEventLoop] = None,
    ):
        self.max_connections = max_connections
        self._loop = loop or asyncio.get_event_loop()

        self._connections: OrderedDict[Host, List["Connection"]] = OrderedDict()
        self._semaphore = asyncio.Semaphore(max_connections)

    async def connect(self, server: Server, port: Port) -> "Connection":
        host = (server, port)

        # enforce the connection limit, releasing connections notifies
        # the semaphore to release here
        await self._semaphore.acquire()

        connections = self._connections.setdefault(host, [])
        # find an un-used connection for this host
        connection = next((conn for conn in connections if not conn.in_use), None)
        if connection is None:
            # disconnect the least-recently-used un-used connection to make space
            # for a new connection. There will be at least one.
            for conns_per_host in reversed(self._connections.values()):
                for conn in conns_per_host:
                    if not conn.in_use:
                        await conn.close()
                        break

            reader, writer = await asyncio.open_connection(server, port)
            connection = Connection(self, host, reader, writer)
            connections.append(connection)

        connection.in_use = True
        # move current host to the front as most-recently used
        self._connections.move_to_end(host, False)

        return connection

    async def close(self):
        """Close all connections"""
        connections = [c for cs in self._connections.values() for c in cs]
        self._connections = OrderedDict()
        for connection in connections:
            await connection.close()

    def _remove(self, connection):
        conns_for_host = self._connections.get(connection._host)
        if not conns_for_host:
            return
        conns_for_host[:] = [c for c in conns_for_host if c != connection]

    def _notify_release(self):
        self._semaphore.release()

    async def __aenter__(self) -> "ConnectionPool":
        return self

    async def __aexit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc: Optional[BaseException],
        tb: Optional[TracebackType],
    ) -> None:
        await self.close()

    def __del__(self) -> None:
        connections = [repr(c) for cs in self._connections.values() for c in cs]
        if not connections:
            return

        context = {
            "pool": self,
            "connections": connections,
            "message": "Unclosed connection pool",
        }
        self._loop.call_exception_handler(context)


class Connection(base):
    def __init__(
        self,
        pool: ConnectionPool,
        host: Host,
        reader: asyncio.StreamReader,
        writer: asyncio.StreamWriter,
    ):
        self._host = host
        self._pool = pool
        self._reader = reader
        self._writer = writer
        self._closed = False
        self.in_use = False

    def __repr__(self):
        host = f"{self._host[0]}:{self._host[1]}"
        return f"Connection<{host}>"

    @property
    def closed(self):
        return self._closed

    def release(self) -> None:
        self.in_use = False
        self._pool._notify_release()

    async def close(self) -> None:
        if self._closed:
            return
        self._closed = True
        self._writer.close()
        self._pool._remove(self)
        try:
            await self._writer.wait_closed()
        except AttributeError:  # wait_closed is new in 3.7
            pass

    def __getattr__(self, name: str) -> Any:
        """All unknown attributes are delegated to the reader and writer"""
        if self._closed or not self.in_use:
            raise ValueError("Can't use a closed or unacquired connection")
        if hasattr(self._reader, name):
            return getattr(self._reader, name)
        return getattr(self._writer, name)

    async def __aenter__(self) -> "Connection":
        if self._closed or not self.in_use:
            raise ValueError("Can't use a closed or unacquired connection")
        return self

    async def __aexit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc: Optional[BaseException],
        tb: Optional[TracebackType],
    ) -> None:
        self.release()

    def __del__(self) -> None:
        if self._closed:
            return
        context = {"connection": self, "message": "Unclosed connection"}
        self._pool._loop.call_exception_handler(context)

请注意，声明在每次查询后连接都将关闭。如果您连接到端口43上的标准WHOIS服务，则无需重新使用套接字

---

在这种情况下，读取器将达到EOF（

reader.at_EOF（）

为true），任何进一步的读取尝试都不会返回任何结果（

reader.read（…）

将始终返回空的

b'

值）。在超时后远程端终止套接字连接之前，写入写入器不会是错误的。您可以将所有需要的内容写入连接，但WHOIS服务器将忽略这些查询。

您连接的是哪种服务器？标准端口43 whois协议没有任何套接字重用选项；连接完成后，服务器将立即关闭连接。这就是为什么要一直读到给出一个空的响应；这意味着读卡器连接现在已关闭。无法读取更多数据。对于保持连接打开的协议，将有一种方法可以检测消息何时完成（如CRLF组合、固定大小的消息或以长度信息开头的消息）。假设您使用的循环在

reader.read（）

返回空值时结束，那么您几乎可以肯定使用的是标准的whois连接。实际上，我正在连接whois服务器，这很有意义，因为我无法通过一些手动测试实现套接字重用。谢谢请纠正我，如果任何以下是错误的想法。多个

task

s可以在

ConnectionPool.connect的while循环中等待多个未来（
fut
s）。这些未来只是作为一种等待的手段。事件循环周期性地检查正在等待的事情；当它找到一个特定的
fut
时，while循环终止，
fut
的
task
获得连接。如果所有这些都是正确的，这是否意味着事件循环中有多个已挂起的
ConnectionPool.connect
方法实例？TIA@wwii：是的，这就是使用期货的意义所在。
connect（）
调用将不会返回，直到可以为该任务提供一个免费连接，我们可以通过让其他任务释放连接来检测该点，并通过未来发出信号，表明可能存在可用的连接。我很好奇，为什么要保持一个显式的获取计数和一个等待者的dict。获取一个
asyncio.Semaphore
，它会自动完成所有工作，这难道不会让代码变得更简单吗？@user4815162342：习惯，胜过一切；我指的是我的漏桶实现供参考，以及其他连接池。aiohttp也使用自己的服务员，但对漏桶和aiohttp池的要求要复杂一些。在这种情况下，信号灯就可以了。@user4815162342谢谢。我还没有在第8页上运行最后一次编辑，哎呀。
async def lookup(pool, server, port, query):
    try:
        conn = await pool.connect(server, port)
    except (ValueError, OSError):
        return {}

    async with conn:
        conn.write(query.encode("ISO-8859-1"))
        await conn.drain()
        data = b""
        while True:
            d = await conn.read(4096)
            if not d:
                break
            data += d
        data = data.decode("ISO-8859-1")
        return data