2016-01-28 17:53 GMT+01:00 Ian Kelly <ian.g.ke...@gmail.com>:
> On Thu, Jan 28, 2016 at 9:40 AM, Frank Millman <fr...@chagford.com> wrote:
>
> > The caller requests some data from the database like this.
> >
> > return_queue = asyncio.Queue()
> > sql = 'SELECT ...'
> > request_queue.put((return_queue, sql))
>
> Note that since this is a queue.Queue, the put call has the potential
> to block your entire event loop.
>
>
Actually, I don't think you actually need an asyncio.Queue.
You could use a simple deque as a buffer, and call fetchmany() when it is
empty, like that (untested):
class AsyncCursor:
"""Wraps a DB cursor and provide async method for blocking operations"""
def __init__(self, cur, loop=None):
if loop is None:
loop = asyncio.get_event_loop()
self._loop = loop
self._cur = cur
self._queue = deque()
def __getattr__(self, attr):
return getattr(self._cur, attr)
def __setattr__(self, attr, value):
return setattr(self._cur, attr, value)
async def execute(self, operation, params):
return await self._loop.run_in_executor(self._cur.execute,
operation, params)
async def fetchall(self):
return await self._loop.run_in_executor(self._cur.fetchall)
async def fetchone(self):
return await self._loop.run_in_executor(self._cur.fetchone)
async def fetchmany(self, size=None):
return await self._loop.run_in_executor(self._cur.fetchmany, size)
async def __aiter__(self):
return self
async def __anext__(self):
if self._queue.empty():
rows = await self.fetchmany()
if not rows:
raise StopAsyncIteration()
self._queue.extend(rows)
return self._queue.popleft()
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