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我正在试验 Python 3.4 的 asyncio 模块。由于没有使用 asyncio 的 MongoDB 生产就绪包，我编写了一个小型包装器类，它在执行程序中执行所有 mongo 查询。这是包装：

import asyncio
from functools import wraps
from pymongo import MongoClient


class AsyncCollection(object):
    def __init__(self, client):
        self._client = client
        self._loop = asyncio.get_event_loop()

    def _async_deco(self, name):
        method = getattr(self._client, name)

        @wraps(method)
        @asyncio.coroutine
        def wrapper(*args, **kwargs):
            print('starting', name, self._client)
            r = yield from self._loop.run_in_executor(None, method, *args, **kwargs)
            print('done', name, self._client, r)
            return r

        return wrapper

    def __getattr__(self, name):
        return self._async_deco(name)


class AsyncDatabase(object):
    def __init__(self, client):
        self._client = client
        self._collections = {}


    def __getitem__(self, col):
        return self._collections.setdefault(col, AsyncCollection(self._client[col]))


class AsyncMongoClient(object):
    def __init__(self, host, port):
        self._client = MongoClient(host, port)
        self._loop = asyncio.get_event_loop()
        self._databases = {}

    def __getitem__(self, db):
        return self._databases.setdefault(db, AsyncDatabase(self._client[db]))

我想异步执行插入，这意味着执行它们的协程不想等待执行完成。asyncio 手册指出A task is automatically scheduled for execution when it is created. The event loop stops when all tasks are done.，所以我构建了这个测试脚本：

from asyncdb import AsyncMongoClient
import asyncio

@asyncio.coroutine
def main():
    print("Started")
    mongo = AsyncMongoClient("host", 27017)
    asyncio.async(mongo['test']['test'].insert({'_id' : 'test'}))
    print("Done")

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

当我运行脚本时，我得到以下结果：

Started
Done
starting insert Collection(Database(MongoClient('host', 27017), 'test'), 'test')

应该有一行表明 mongo 查询已完成。当我yield from使用这个协程而不是使用asyncio.async. 然而，真正奇怪的是，当我运行这个 corouting using 时，测试条目实际上存在于 MongoDB 中asyncio.async，所以尽管它似乎有效，但我不明白为什么我看不到指示查询有的打印语句被执行。尽管我使用 运行事件循环run_until_completed，但它应该等待插入任务完成，即使主协程之前完成。

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1 回答 1

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asyncio.async(mongo...))只是安排mongo 查询。并且run_until_complete()不等待它。这是使用协程显示它的代码示例asyncio.sleep()：

#!/usr/bin/env python3
import asyncio
from contextlib import closing
from timeit import default_timer as timer

@asyncio.coroutine
def sleep_BROKEN(n):
    # schedule coroutine; it runs on the next yield
    asyncio.async(asyncio.sleep(n))

@asyncio.coroutine
def sleep(n):
    yield from asyncio.sleep(n)

@asyncio.coroutine
def double_sleep(n):
    f = asyncio.async(asyncio.sleep(n))
    yield from asyncio.sleep(n) # the first sleep is also started
    yield from f

n = 2
with closing(asyncio.get_event_loop()) as loop:
    start = timer()
    loop.run_until_complete(sleep_BROKEN(n))
    print(timer() - start)
    loop.run_until_complete(sleep(n))
    print(timer() - start)
    loop.run_until_complete(double_sleep(n))
    print(timer() - start)

输出

0.0001221800921484828
2.002586881048046
4.005100341048092

输出显示run_until_complete(sleep_BROKEN(n))在不到 2 毫秒而不是 2 秒内返回。并且run_until_complete(sleep(n))可以正常工作：它会在 2 秒内返回。double_sleep()显示调度的协程async.async()正在运行yield from（两个并发睡眠并行），即它睡眠 2 秒，而不是 4 秒。如果您在第一个之前添加延迟（不允许事件循环运行），yield from那么您会看到yield from f没有早点返回，即asyncio.async不运行协程；它只安排它们运行。

于 2014-05-04T10:59:56.183 回答