Hi,
In Gnulib, we have a unit test that compiles the program below as a
native Windows program (either with mingw or with MSVC), that exercises
the Gnulib select() function
<https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=lib/select.c;h=5a58d6ee47f5b10413d97cb7a1996d424eefc796;hb=HEAD>
Then it does (in a Cygwin shell):
rm -f t-select-in.tmp
./test-select-fd.exe r 0 t-select-in.tmp < /dev/null
cat t-select-in.tmp
Up to Cygwin 3.6.0, the contents of the file t-select-in.tmp was "1",
like on most other OSes, indicating that the program can read() from
file descriptor 0.
In Cygwin 3.6.1, the contents of the file t-select-in.tmp is "0",
indicating that read()ing from file descriptor 0 would block.
This is a regression.
Looking through the commits between 3.6.0 and 3.6.1, the most likely culprit
is commit d750786e7de013b58e2968eeb6a7fd59dcc535c9 .
Bruno
=============================== test-select-fd.c ===============================
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/select.h>
int
main (int argc, char *argv[])
{
if (argc == 4)
{
char mode = argv[1][0];
if (mode == 'r' || mode == 'w')
{
int fd = atoi (argv[2]);
if (fd >= 0)
{
const char *result_file_name = argv[3];
FILE *result_file = fopen (result_file_name, "wb");
if (result_file != NULL)
{
fd_set fds;
struct timeval timeout;
int ret;
FD_ZERO (&fds);
FD_SET (fd, &fds);
timeout.tv_sec = 0;
timeout.tv_usec = 10000;
ret = (mode == 'r'
? select (fd + 1, &fds, NULL, NULL, &timeout)
: select (fd + 1, NULL, &fds, NULL, &timeout));
if (ret < 0)
{
perror ("select failed");
exit (1);
}
if ((ret == 0) != ! FD_ISSET (fd, &fds))
{
fprintf (stderr, "incorrect return value\n");
exit (1);
}
fprintf (result_file, "%d\n", ret);
exit (0);
}
}
}
}
fprintf (stderr, "Usage: test-select-fd mode fd result-file-name\n");
exit (1);
}
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