On Wed, 25 Jun 2025 14:07:15 +0200 (CEST)
Johannes Schindelin wrote:
> Hi Takashi,
>
> On Wed, 25 Jun 2025, Takashi Yano wrote:
>
> > On Wed, 25 Jun 2025 19:55:34 +0900
> > Takashi Yano wrote:
> > >
> > > On Wed, 25 Jun 2025 09:38:17 +0200 (CEST)
> > > Johannes Schindelin wrote:
> > > >
> > > > On Wed, 25 Jun 2025, Johannes Schindelin wrote:
> > > >
> > > > > On Wed, 25 Jun 2025, Takashi Yano wrote:
> > > > >
> > > > > > I'd revise the patch as follows. Could you please test if the
> > > > > > following patch also solves the issue?
> > > > >
> > > > > Will do.
> > > >
> > > > For the record, in my tests, this fixed the hangs, too.
> > >
> > > Thanks for testing.
> > > However, I noticed that this patch changes the behavior Corinna was
> > > concerned about.
> >
> > The behaviour change can be checked using attached test case.
>
> I do not understand what this undocumented code is trying to demonstrate,
> not without any explanation.
>
> Could you rework it so that it becomes a proper test in the test suite
> that verifies that Cygwin behaves as desired, please?
What the comment in the source code says:
/* NtWriteFile returns success with # of bytes written == 0 if writing
on a non-blocking pipe fails because the pipe buffer doesn't have
sufficient space.
POSIX requires
- A write request for {PIPE_BUF} or fewer bytes shall have the
following effect: if there is sufficient space available in the
pipe, write() shall transfer all the data and return the number
of bytes requested. Otherwise, write() shall transfer no data and
return -1 with errno set to [EAGAIN].
- A write request for more than {PIPE_BUF} bytes shall cause one
of the following:
- When at least one byte can be written, transfer what it can and
return the number of bytes written. When all data previously
written to the pipe is read, it shall transfer at least {PIPE_BUF}
bytes.
- When no data can be written, transfer no data, and return -1 with
errno set to [EAGAIN]. */
/* Independent of being blocking or non-blocking, if we're here,
the pipe has less space than requested. If the pipe is a
non-Cygwin pipe, just try the old strategy of trying a half
write. If the pipe has at
least PIPE_BUF bytes available, try to write all matching
PIPE_BUF sized blocks. If it's less than PIPE_BUF, try
the next less power of 2 bytes. This is not really the Linux
strategy because Linux is filling the pages of a pipe buffer
in a very implementation-defined way we can't emulate, but it
resembles it closely enough to get useful results. */
--
Takashi Yano <[email protected]>
