使用异步协程并行运行函数？

Question

我有下面的代码，从数据库(read_db)读取数据，并将数据写入拼图文件(data.to_parquet)。这两个I/O操作都需要一段时间才能运行。

def main():
    while id < 1000:
       logging.info(f'reading - id: {id}')
       data = read_db(id) # returns a dataframe

       logging.info(f'saving - id: {id}')
       data.to_parquet(f'{id}.parquet')
       logging.info(f'saved - id: {id}')

       id += 1

它很慢，所以我希望同时运行read_db(n+1)和to_parquet(n)。我需要让id的每一步都按顺序完成(read_db(n+1)需要在read_db(n)之后运行，data.to_parquet(n+1)需要在data.to_parquet(n)之后运行)。下面是异步版本

def async_wrap(f):
    @wraps(f)
    async def run(*args, loop=None, executor=None, **kwargs):
        if loop is None:
            loop = asyncio.get_event_loop()
        p = partial(f, *args, **kwargs)
        return await loop.run_in_executor(executor, p)
    return run

async def main():
    read_db_async = async_wrap(read_db)
    while id < 1000:
       logging.info(f'reading - id: {id}')
       data = await read_db_async(id) # returns a dataframe

       logging.info(f'saving - id: {id}')
       to_parquet_async = async_wrap(data.to_parquet)
       await data.to_parquet(f'{id}.parquet')
       logging.info(f'saved - id: {id}')

       id += 1

asyncio.get_event_loop().run_until_complete(main())

我希望看到一些乱七八糟的日志：

reading - id: 1
saving - id: 1      (saving 1 and reading 2 run in parallel)
reading - id: 2
saved - id: 1
saving - id: 2
reading - id: 3
saved - id: 2
.....

但是，实际上同步代码的日志是相同的吗？

reading - id: 1
saving - id: 1
saved - id: 1
reading - id: 2
saving - id: 2
saved - id: 2
reading - id: 3
.....

Answer 1

您可以通过使用gather或等效工具来同时运行read_db(n+1)和to_parquet(n)：

async def main():
    read_db_async = async_wrap(read_db)
    prev_to_parquet = asyncio.sleep(0)  # no-op

    for id in range(1, 1000):
        data, _ = await asyncio.gather(read_db_async(id), prev_to_parquet)
        to_parquet_async = async_wrap(data.to_parquet)
        prev_to_parquet = to_parquet_async(f'{id}.parquet')

    await prev_to_parquet