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Date: Tue, 15 Apr 2025 17:20:46 +0900
To: cygwin AT cygwin DOT com
Cc: Bruno Haible <bruno AT clisp DOT org>
Subject: Re: /dev/null regression in Cygwin 3.6.1
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Mon, 14 Apr 2025 15:03:16 +0200
Bruno Haible wrote:
> Here's a smaller reproducer.
> 
> ============================ foo.c ============================
> #include <stdio.h>
> #include <windows.h>
> #include <io.h>
> 
> int main ()
> {
>   HANDLE h = (HANDLE) _get_osfhandle (0);
>   fprintf (stderr, "h = 0x%08x\n", h);
>   fprintf (stderr, "FileType is CHAR ? %d\n", GetFileType (h) == FILE_TYPE_CHAR);
>   int ret = WaitForSingleObject (h, 0);
>   if (ret == WAIT_OBJECT_0)
>     fprintf (stderr, "WaitForSingleObject -> WAIT_OBJECT_0\n");
>   else if (ret == WAIT_TIMEOUT)
>     fprintf (stderr, "WaitForSingleObject -> WAIT_TIMEOUT\n");
>   else if (ret == WAIT_ABANDONED)
>     fprintf (stderr, "WaitForSingleObject -> WAIT_ABANDONED\n");
>   else if (ret == WAIT_FAILED)
>     fprintf (stderr, "WaitForSingleObject -> WAIT_FAILED\n");
> }
> ===============================================================
> Compile this file as a native Windows program (mingw for example).
> Then, in a Cygwin shell window, do
> $ ./a < /dev/null
> 
> Result in 3.4.6:
> 
> h = 0x000001e8
> FileType is CHAR ? 1
> WaitForSingleObject -> WAIT_OBJECT_0
> 
> Result in 3.6.1:
> 
> h = 0x00000358
> FileType is CHAR ? 1
> WaitForSingleObject -> WAIT_TIMEOUT
> 
> > Looking through the commits between 3.6.0 and 3.6.1, the most likely culprit
> > is commit d750786e7de013b58e2968eeb6a7fd59dcc535c9 .
> 
> Especially since this commit modified select.cc, removing a comment
>   /* TODO: Buffer really full or non-Cygwin reader? */
> and here we are exactly in that case: a non-Cygwin process reading from
> Cygwin's /dev/null.
> 
> Takashi Yano, can you please look at it and restore the previous behaviour?

Thanks for the new testcase. I think the issue has been fixed in:
cygwin-3.7.0-0.68.g37c49decc835 (Test)
Please test.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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