On Wed, 29 Nov 2017, Corinna Vinschen wrote:
On Nov 29 13:36, Corinna Vinschen wrote:
On Nov 29 13:04, Corinna Vinschen wrote:
- If you do async IO, you have to handle STATUS_PENDING gracefully:
- The IO_STATUS_BLOCK given to NtWriteFile *must* exist for the
entire time the operation takes after NtWriteFile returned
STATUS_PENDING. An IO_STATUS_BLOCK fhandler member comes to mind,
maybe fhandler_base_overlapped::io_status can be reused.
No, wait. There can be more than one outstanding aio operations on the
same descriptor. Therefore the IO_STATUS_BLOCK must be connected to the
aiocb struct one way or the other, becasue only that struct is local to
the aio operation.
I guess that's what the Linux man page aio(7) subsumes under
struct aiocb {
[...]
/* Various implementation-internal fields not shown */
};
Yes, I believe that's correct. But in my aio implementation for Cygwin,
I'm not using overlapped I/O or any kind of async or nonblocking write.
I'm using separate threads to do plain vanilla blocking writes (via pwrite
if able). I'm doing this because I'm operating with user-supplied file
descriptors that might or might not be underlain with async-capable
Windows handles.
(It's my understanding that if one wants to do overlapped I/O on a Windows
handle, one has to request that explicitly when creating the handle. I
don't think Cygwin does this by default. Corrections welcome.)
So in this environment seeing pwrite() return with a short write count,
even though it's understandable that the underlying Windows write might
still be underway, is a real problem. Because, if I use the short count
to determine that I need to write the remainder of a buffer, it'll have
been written twice: once by the late-finishing pwrite and again by the
recovery code.
A blocking pwrite() (i.e., not overlapped or async in any way) has to wait
for the underlying NtWriteFile() to complete in order to get a correct
write count and/or correct final status code, doesn't it?
..mark
P.S. I'll look into IRC clients. You've suggested it before and I just
recall the wild IRC days in the 90s with egg drops and bots and bans and
it seemed like a time sink I couldn't afford. Maybe #cygwin-developers
on freenode is more civilized :-)).
