Asynchronous 异步写入文件

我一直在尝试创建一个服务器进程，该进程从客户端进程异步接收输入文件路径和输出路径。服务器执行一些依赖于数据库的转换，但是为了简单起见，让我们假设它只是将所有内容放在大写形式。以下是服务器的一个玩具示例：

import asyncio
import aiofiles as aiof
import logging
import sys


ADDRESS = ("localhost", 10000)

logging.basicConfig(level=logging.DEBUG,
                    format="%(name)s: %(message)s",
                    stream=sys.stderr)

log = logging.getLogger("main")
loop = asyncio.get_event_loop()


async def server(reader, writer):
    log = logging.getLogger("process at {}:{}".format(*ADDRESS))
    paths = await reader.read()
    in_fp, out_fp = paths.splitlines()
    log.debug("connection accepted")
    log.debug("processing file {!r}, writing output to {!r}".format(in_fp, out_fp))
    async with aiof.open(in_fp, loop=loop) as inp, aiof.open(out_fp, "w", loop=loop) as out:
        async for line in inp:
            out.write(line.upper())
        out.flush()
    writer.write(b"done")
    await writer.drain()
    log.debug("closing")
    writer.close()
    return


factory = asyncio.start_server(server, *ADDRESS)
server = loop.run_until_complete(factory)
log.debug("starting up on {} port {}".format(*ADDRESS))

try:
    loop.run_forever()
except KeyboardInterrupt:
    pass
finally:
    log.debug("closing server")
    server.close()
    loop.run_until_complete(server.wait_closed())
    log.debug("closing event loop")
    loop.close()

客户：

import asyncio
import logging
import sys
import random

ADDRESS = ("localhost", 10000)
MESSAGES = ["/path/to/a/big/file.txt\n", 
            "/output/file_{}.txt\n".format(random.randint(0, 99999))]

logging.basicConfig(level=logging.DEBUG,
                    format="%(name)s: %(message)s",
                    stream=sys.stderr)

log = logging.getLogger("main")
loop = asyncio.get_event_loop()

async def client(address, messages):
    log = logging.getLogger("client")
    log.debug("connecting to {} port {}".format(*address))
    reader, writer = await asyncio.open_connection(*address)
    writer.writelines([bytes(line, "utf8") for line in messages])
    if writer.can_write_eof():
        writer.write_eof()
    await writer.drain()

    log.debug("waiting for response")
    response = await reader.read()
    log.debug("received {!r}".format(response))
    writer.close()
    return


try:
    loop.run_until_complete(client(ADDRESS, MESSAGES))
finally:
    log.debug("closing event loop")
    loop.close()

我一次激活了服务器和几个客户端。服务器的日志：

asyncio: Using selector: KqueueSelector
main: starting up on localhost port 10000
process at localhost:10000: connection accepted
process at localhost:10000: processing file b'/path/to/a/big/file.txt', writing output to b'/output/file_79609.txt'
process at localhost:10000: connection accepted
process at localhost:10000: processing file b'/path/to/a/big/file.txt', writing output to b'/output/file_68917.txt'
process at localhost:10000: connection accepted
process at localhost:10000: processing file b'/path/to/a/big/file.txt', writing output to b'/output/file_2439.txt'
process at localhost:10000: closing
process at localhost:10000: closing
process at localhost:10000: closing

所有客户端都打印此文件：

asyncio: Using selector: KqueueSelector
client: connecting to localhost port 10000
client: waiting for response
client: received b'done'
main: closing event loop

---

输出文件已创建，但仍为空。我相信他们没有被冲。我能修好它吗

在

out.write（）和
out.flush（）之前，您缺少一个
wait
：

但是，我强烈建议尝试跳过所有文件，使用常规的、同步的磁盘I/O，并为网络活动保持异步：

with open(file, "w") as out:  # regular file I/O
    async for s in network_request():  # asyncio for slow network work. measure it!
        out.write(s) # should be really quick, measure it!

使用同步文件IO有点破坏了异步服务器的整体功能。它不是在客户机连接到来时处理它们，而是将它们排列在队列中，并且只在前一项处理完成后接收下一项。这没关系，如果客户端没有达到超时，它可以。除非I/O非常快。缓存和SSD磁盘可能会产生很好的效果，而当前的Aiofile实现甚至可能会导致速度减慢（使用线程延迟io而不是事件）
with open(file, "w") as out:  # regular file I/O
    async for s in network_request():  # asyncio for slow network work. measure it!
        out.write(s) # should be really quick, measure it!