It is legal to call batchWait with already completed operations in the
ring. In such case, we need to avoid waiting in the syscall. The
any_done flag was a poor way of tracking state we already have: whether
the completion queue is empty.
This problem affects the posix poll implementation as well.
Thanks again to jacobly for finding the problem.
and make reading file streaming allowed to return 0 byte reads.
According to Microsoft documentation, on Windows it is possible to get
0-byte reads from pipes when 0-byte writes are made.
The defer would cause two problems:
1. keeping the state active during call to NtCancelIoFile
2. invalid state transition. after canceled is returned from
checkCancel, new status is already canceled. calling finish after
that is illegal.
reasoning is that polling with large amount of operations will be rarely
done with std.Io.Threaded. However this still provides the opportunity
to provide concurrency for any real world use cases that need it.
This commit shows a proof-of-concept direction for std.Io.VTable to go,
which is to have general support for batching, timeouts, and
non-blocking.
I'm not sure if this is a good idea or not so I'm putting it up for
scrutiny.
This commit introduces `std.Io.operate`, `std.Io.Operation`, and
implements it experimentally for `FileReadStreaming`.
In `std.Io.Threaded`, the implementation is based on poll().
This commit shows how it can be used in `std.process.run` to collect
both stdout and stderr in a single-threaded program using
`std.Threaded.Io`.
It also demonstrates how to upgrade code that was previously using
`std.Io.poll` (*not* integrated with the interface!) using concurrency.
This may not be ideal since it makes the build runner no longer support
single-threaded mode. There is still a needed abstraction for
conveniently reading multiple File streams concurrently without
io.concurrent, but this commit demonstrates that such an API can be
built on top of the new `std.Io.operate` functionality.
When `NtReadFile` returns `SUCCESS`, the APC routine still runs when
next alertable, which was previously clobbering an out of scope `done`.
Instead of adding an extra syscall to the success path, avoid all APC
side effects, allowing instant completions to return immediately.
Andrew Kelley