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/* Assist in file system timestamp tests.
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Copyright (C) 2009-2017 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* Written by Eric Blake <ebb9@byu.net>, 2009. */
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#ifndef GLTEST_NAP_H
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# define GLTEST_NAP_H
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# include <limits.h>
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# include <stdbool.h>
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/* Name of the witness file. */
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#define TEMPFILE BASE "nap.tmp"
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/* File descriptor used for the witness file. */
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static int nap_fd = -1;
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/* Return A - B, in ns.
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Return 0 if the true result would be negative.
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Return INT_MAX if the true result would be greater than INT_MAX. */
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static int
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diff_timespec (struct timespec a, struct timespec b)
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{
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time_t as = a.tv_sec;
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time_t bs = b.tv_sec;
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int ans = a.tv_nsec;
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int bns = b.tv_nsec;
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if (! (bs < as || (bs == as && bns < ans)))
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return 0;
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if (as - bs <= INT_MAX / 1000000000)
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{
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int sdiff = (as - bs) * 1000000000;
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int usdiff = ans - bns;
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if (usdiff < INT_MAX - sdiff)
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return sdiff + usdiff;
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}
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return INT_MAX;
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}
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/* If DO_WRITE, bump the modification time of the file designated by NAP_FD.
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Then fetch the new STAT information of NAP_FD. */
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static void
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nap_get_stat (struct stat *st, int do_write)
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{
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if (do_write)
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{
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ASSERT (write (nap_fd, "\n", 1) == 1);
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#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
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/* On native Windows, the modification times are not changed until NAP_FD
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is closed. See
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https://msdn.microsoft.com/en-us/library/windows/desktop/aa365747(v=vs.85).aspx */
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close (nap_fd);
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nap_fd = open (TEMPFILE, O_RDWR, 0600);
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ASSERT (nap_fd != -1);
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lseek (nap_fd, 0, SEEK_END);
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#endif
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}
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ASSERT (fstat (nap_fd, st) == 0);
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}
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/* Given a file whose descriptor is FD, see whether delaying by DELAY
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nanoseconds causes a change in a file's mtime.
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OLD_ST is the file's status, recently gotten. */
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static bool
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nap_works (int delay, struct stat old_st)
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{
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struct stat st;
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struct timespec delay_spec;
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delay_spec.tv_sec = delay / 1000000000;
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delay_spec.tv_nsec = delay % 1000000000;
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ASSERT (nanosleep (&delay_spec, 0) == 0);
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nap_get_stat (&st, 1);
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if (diff_timespec (get_stat_mtime (&st), get_stat_mtime (&old_st)))
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return true;
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return false;
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}
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static void
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clear_temp_file (void)
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{
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if (0 <= nap_fd)
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{
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ASSERT (close (nap_fd) != -1);
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ASSERT (unlink (TEMPFILE) != -1);
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}
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}
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/* Sleep long enough to notice a timestamp difference on the file
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system in the current directory. Use an adaptive approach, trying
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to find the smallest delay which works on the current file system
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to make the timestamp difference appear. Assert a maximum delay of
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~2 seconds, more precisely sum(2^n) from 0 to 30 = 2^31 - 1 = 2.1s.
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Assumes that BASE is defined, and requires that the test module
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depends on nanosleep. */
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static void
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nap (void)
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{
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struct stat old_st;
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static int delay = 1;
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if (-1 == nap_fd)
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{
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atexit (clear_temp_file);
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ASSERT ((nap_fd = creat (TEMPFILE, 0600)) != -1);
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nap_get_stat (&old_st, 0);
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}
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else
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{
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ASSERT (0 <= nap_fd);
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nap_get_stat (&old_st, 1);
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}
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if (1 < delay)
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delay = delay / 2; /* Try half of the previous delay. */
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ASSERT (0 < delay);
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for (;;)
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{
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if (nap_works (delay, old_st))
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return;
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if (delay <= (2147483647 - 1) / 2)
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{
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delay = delay * 2 + 1;
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continue;
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}
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else
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break;
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}
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/* Bummer: even the highest nap delay didn't work. */
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ASSERT (0);
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}
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#endif /* GLTEST_NAP_H */
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