Failing to check for closed socket causes future to spin, hogging executor thread about smol HOT 2 CLOSED

I think that your two futures in spawn_connections could be implemented using smol::io::copy, which properly handles checking for zero-sized reads indicating EOF.

One of the main architectural differences between Tokio and Smol is that Tokio's reactor uses edge-triggered polling while Smol's uses oneshot polling. The intuitive way to think about this is:

• Tokio checks for incoming data on the socket and then reads from it.
• Smol tries to read/write/whatever from the socket, and if there is no data, waits for new data.

In most cases the user facing differences between these two approaches is not noticeable. However, since there is no more incoming data Tokio returns Poll::Pending when trying to read from a closed socket. On the other hand Smol returns Poll::Ready(0).

from smol.

I think that your two futures in spawn_connections could be implemented using smol::io::copy, which properly handles checking for zero-sized reads indicating EOF.

This was just a minimal example. In my actual code, I perform some modifications to the stream, so copy wouldn't be a viable option.

One of the main architectural differences between Tokio and Smol is that Tokio's reactor uses edge-triggered polling while Smol's uses oneshot polling.

Yes, I was at least tangentially aware of this. I encountered the problem above in integration tests using tokio/smol, but my actual code uses mio directly. And since mio doesn't have configurable polling, I had to adapt my code for edge-triggering. I only later discovered polling. I wish I would have seen it earlier, since level-triggering would have been more appropriate for my situation.

However, since there is no more incoming data Tokio returns Poll::Pending when trying to read from a closed socket. On the other hand Smol returns Poll::Ready(0).

I thought this might be a conscious design decision, but I wasn't sure. Thanks for clarifying. I'll be sure to keep that difference in mind in the future.

Thanks for answering my question.

from smol.