[Twisted-Python] yielding from within deferToThread

[Naveen Michaud-Agrawal]

To answer my own question, it looks like i can just pass sqlalchemy's
ResultProxy into deferToThread to make a blocking call to fetch the next
set of results:

@defer.inlineCallbacks
def stream_results():
    engine = sqlalchemy.create_engine(...)
    query = "select * from table"
    proxy = yield threads.deferToThread(engine.execute, query)
    while True:
        results = yield threads.deferToThread(proxy.fetchmany, 1000)
        if not results:
            break
        print results



On Thu, Dec 3, 2015 at 2:41 PM, Naveen Michaud-Agrawal <
naveen.michaudagrawal at gmail.com> wrote:

> I'm trying to use sqlalchemy from a twisted application (by running all
> blocking queries using deferToThread). Is it possible to yield from within
> the function running in deferToThread? For example:
>
>
> def threadRunQuery(engine, query):
>     conn = engine.connect()
>     res = conn.execute(query)
>
>     while True:
>         results = res.fetchmany(1000)
>         if not results:
>             break
>         yield results
>
>
> @defer.inlineCallbacks
> def stream_results():
>     engine = sqlalchemy.create_engine(...)
>     query = "select * from table"
>     result_iter = yield threads.deferToThread(threadRunQuery, engine,
> query)
>     for results in result_iter:
>         print results
>
>
> It seems that the thread returns a generator, and so everything within
> threadRunQuery is actually running on the main reactor thread. Is there
> anyway to stream back results from a deferToThread?
>
> Regards
> Naveen Michaud-Agrawal
>



-- 
-----------------------------------
Naveen Michaud-Agrawal
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