tests/nap.h

   1 /* Assist in file system timestamp tests.
   2    Copyright (C) 2009-2024 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Eric Blake <ebb9@byu.net>, 2009.  */
  18
  19 #ifndef GLTEST_NAP_H
  20 # define GLTEST_NAP_H
  21
  22 # include <limits.h>
  23
  24 # include <stdckdint.h>
  25
  26 /* Avoid a conflict with a function called nap() on UnixWare.  */
  27 # if defined _SCO_DS || (defined __SCO_VERSION__ || defined __sysv5__)  /* OpenServer, UnixWare */
  28 #  include <unistd.h>
  29 #  undef nap
  30 #  define nap gl_nap
  31 # endif
  32
  33 /* Name of the witness file.  */
  34 #define TEMPFILE BASE "nap.tmp"
  35
  36 /* File descriptor used for the witness file.  */
  37 static int nap_fd = -1;
  38
  39 /* Return A - B, in ns.
  40    Return 0 if the true result would be negative.
  41    Return INT_MAX if the true result would be greater than INT_MAX.  */
  42 static int
  43 diff_timespec (struct timespec a, struct timespec b)
  44 {
  45   time_t as = a.tv_sec;
  46   time_t bs = b.tv_sec;
  47   int ans = a.tv_nsec;
  48   int bns = b.tv_nsec;
  49   int sdiff;
  50
  51   ASSERT (0 <= ans && ans < 2000000000);
  52   ASSERT (0 <= bns && bns < 2000000000);
  53
  54   if (! (bs < as || (bs == as && bns < ans)))
  55     return 0;
  56
  57   if (ckd_sub (&sdiff, as, bs)
  58       || ckd_mul (&sdiff, sdiff, 1000000000)
  59       || ckd_add (&sdiff, sdiff, ans - bns))
  60     return INT_MAX;
  61
  62   return sdiff;
  63 }
  64
  65 /* If DO_WRITE, bump the modification time of the file designated by NAP_FD.
  66    Then fetch the new STAT information of NAP_FD.  */
  67 static void
  68 nap_get_stat (struct stat *st, int do_write)
  69 {
  70   if (do_write)
  71     {
  72       ASSERT (write (nap_fd, "\n", 1) == 1);
  73 #if defined _WIN32 || defined __CYGWIN__
  74       /* On Windows, the modification times are not changed until NAP_FD
  75          is closed. See
  76          <https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-writefile> */
  77       close (nap_fd);
  78       nap_fd = open (TEMPFILE, O_RDWR, 0600);
  79       ASSERT (nap_fd != -1);
  80       lseek (nap_fd, 0, SEEK_END);
  81 #endif
  82     }
  83   ASSERT (fstat (nap_fd, st) == 0);
  84 }
  85
  86 /* Given a file whose descriptor is FD, see whether delaying by DELAY
  87    nanoseconds causes a change in a file's mtime.
  88    OLD_ST is the file's status, recently gotten.  */
  89 static bool
  90 nap_works (int delay, struct stat old_st)
  91 {
  92   struct stat st;
  93   struct timespec delay_spec;
  94   delay_spec.tv_sec = delay / 1000000000;
  95   delay_spec.tv_nsec = delay % 1000000000;
  96   ASSERT (nanosleep (&delay_spec, 0) == 0);
  97   nap_get_stat (&st, 1);
  98
  99   if (diff_timespec (get_stat_mtime (&st), get_stat_mtime (&old_st)))
 100     return true;
 101
 102   return false;
 103 }
 104
 105 static void
 106 clear_temp_file (void)
 107 {
 108   if (0 <= nap_fd)
 109     {
 110       ASSERT (close (nap_fd) != -1);
 111       ASSERT (unlink (TEMPFILE) != -1);
 112     }
 113 }
 114
 115 /* Sleep long enough to notice a timestamp difference on the file
 116    system in the current directory.  Use an adaptive approach, trying
 117    to find the smallest delay which works on the current file system
 118    to make the timestamp difference appear.  Assert a maximum delay of
 119    ~2 seconds, more precisely sum(2^n) from 0 to 30 = 2^31 - 1 = 2.1s.
 120    Assumes that BASE is defined, and requires that the test module
 121    depends on nanosleep.  */
 122 static void
 123 nap (void)
 124 {
 125   struct stat old_st;
 126   static int delay = 1;
 127
 128   if (-1 == nap_fd)
 129     {
 130       atexit (clear_temp_file);
 131       ASSERT ((nap_fd = creat (TEMPFILE, 0600)) != -1);
 132       nap_get_stat (&old_st, 0);
 133     }
 134   else
 135     {
 136       ASSERT (0 <= nap_fd);
 137       nap_get_stat (&old_st, 1);
 138     }
 139
 140   if (1 < delay)
 141     delay = delay / 2;  /* Try half of the previous delay.  */
 142   ASSERT (0 < delay);
 143
 144   for (;;)
 145     {
 146       if (nap_works (delay, old_st))
 147         return;
 148       if (delay <= (2147483647 - 1) / 2)
 149         {
 150           delay = delay * 2 + 1;
 151           continue;
 152         }
 153       else
 154         break;
 155     }
 156
 157   /* Bummer: even the highest nap delay didn't work. */
 158   ASSERT (0);
 159 }
 160
 161 #endif /* GLTEST_NAP_H */