Corinna Vinschen wrote:
On Nov 28 00:03, Mark Geisert wrote:
Mark Geisert wrote:
---
winsup/cygwin/fhandler_disk_file.cc | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/winsup/cygwin/fhandler_disk_file.cc
b/winsup/cygwin/fhandler_disk_file.cc
index 5dfcae4d9..2ead9948c 100644
[...]
Oops, I neglected to include an explanatory comment. Issuing simultaneous
pwrite(s) on one file descriptor from multiple threads, as one might do in a
forthcoming POSIX aio implementation, sometimes results in garbage status in
the IO_STATUS_BLOCK on return from NtWriteFile(). Zeroing beforehand made
the issue go away.
This is mildly concerning to me because there are many other uses of
IO_STATUS_BLOCK in the Cygwin DLL that haven't seemed to have needed
initialization.
Puzzledly,
Ok, let's start with, why did you tweak pread if you only observed
a problem in pwrite?
Optimism? :-) No, you're correct; I was getting ahead of myself.
In terms of pread, we already have a very recent
patch series:
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=46702f92ea49
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=c983aa48798d
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=181fe5d2edac
In this case it turned out that the problem was related to hitting EOF.
I wonder if we hit a similar problem here.
Two points:
- Did you check the status code returned by NtWriteFile? Not all non-0
status codes fail the !NT_SUCCESS (status) test.
I did check the status code but don't recall what it was. The symptom I was
seeing was outlandish io.Information values being returned by pwrite(). Far
larger than the number requested in the call to pwrite() and NtWriteFile().
- Do you have a simple, self-contained testcase?
That would be difficult. I can supply an strace excerpt just showing the region
of these simultaneous pwrite() calls, without this patch. If it's too large
I'll put it somewhere and post a link (but I don't think it will be).
..mark
