This repo provides a minimal breaking example for edge triggered behavior
on Windows. Mio aims to support edge-triggered behavior, which means it "only delivers
events when changes occur on the monitored file descriptor" (from
epoll docs describing EPOLLET).
This program does the following:
- Initialize a TcpListener and connect a TcpStream. The listener writes back anything that it receives from the stream
- Registers for read + write events on the stream
- Writes to the stream + waits until it is readable
- Reads from the stream
- Writes to the stream + waits until it is readable
When run with cargo run, this program will exit cleanly on macos + linux
but will panic on windows.
On Windows, in step 5 we never receive a readable notification. This is because on Windows the selector clears the source's interest flags on event receipt (e.g. this occurs in step 3 here). The flags are reset by re-registering which occurs only after a non-blocking i/o operation (see here).
The discrepancy can be "fixed" by adding a non-blocking read after 4, as is
done in most (all?) of the
tests in mio where this difference might
surface .
To be fully consistent with the EPOLLET from epoll, step 4 of
completing a successful read operation should reset (at least) the
readable interest on the source.