calling `executemany` async concurrently leads to "Segamentation fault"

I'm using `aioodbc` to talk to MySQL. `executemany` works for me in inserting many rows into a table. Hoping to increase throughput, I tried to async call `executemany` concurrently like this:

```
async for x in data:
task = asyncio.ensure_future(cursor.executemany(...))
await queue.put(task)
```

The queue has capacity 10. This leads to `Segmentation fault` w/o any additional info. I guess this has to do with the interaction between async and threads, but don't know for sure. Any idea why this is happening? Thanks.