inet/deadline.c

   1 /* Computing deadlines for timeouts.
   2    Copyright (C) 2017-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <net-internal.h>
  20
  21 #include <assert.h>
  22 #include <limits.h>
  23 #include <stdio.h>
  24 #include <stdint.h>
  25 #include <time.h>
  26
  27 struct deadline_current_time
  28 __deadline_current_time (void)
  29 {
  30   struct deadline_current_time result;
  31   if (__clock_gettime (CLOCK_MONOTONIC, &result.current) != 0)
  32     {
  33       struct timeval current_tv;
  34       if (__gettimeofday (&current_tv, NULL) == 0)
  35         __libc_fatal ("Fatal error: gettimeofday system call failed\n");
  36       result.current.tv_sec = current_tv.tv_sec;
  37       result.current.tv_nsec = current_tv.tv_usec * 1000;
  38     }
  39   assert (result.current.tv_sec >= 0);
  40   return result;
  41 }
  42
  43 /* A special deadline value for which __deadline_is_infinite is
  44    true.  */
  45 static inline struct deadline
  46 infinite_deadline (void)
  47 {
  48   return (struct deadline) { { -1, -1 } };
  49 }
  50
  51 struct deadline
  52 __deadline_from_timeval (struct deadline_current_time current,
  53                          struct timeval tv)
  54 {
  55   assert (__is_timeval_valid_timeout (tv));
  56
  57   /* Compute second-based deadline.  Perform the addition in
  58      uintmax_t, which is unsigned, to simply overflow detection.  */
  59   uintmax_t sec = current.current.tv_sec;
  60   sec += tv.tv_sec;
  61   if (sec < (uintmax_t) tv.tv_sec)
  62     return infinite_deadline ();
  63
  64   /* Compute nanosecond deadline.  */
  65   int nsec = current.current.tv_nsec + tv.tv_usec * 1000;
  66   if (nsec >= 1000 * 1000 * 1000)
  67     {
  68       /* Carry nanosecond overflow to seconds.  */
  69       nsec -= 1000 * 1000 * 1000;
  70       if (sec + 1 < sec)
  71         return infinite_deadline ();
  72       ++sec;
  73     }
  74   /* This uses a GCC extension, otherwise these casts for detecting
  75      overflow would not be defined.  */
  76   if ((time_t) sec < 0 || sec != (uintmax_t) (time_t) sec)
  77     return infinite_deadline ();
  78
  79   return (struct deadline) { { sec, nsec } };
  80 }
  81
  82 int
  83 __deadline_to_ms (struct deadline_current_time current,
  84                   struct deadline deadline)
  85 {
  86   if (__deadline_is_infinite (deadline))
  87     return INT_MAX;
  88
  89   if (current.current.tv_sec > deadline.absolute.tv_sec
  90       || (current.current.tv_sec == deadline.absolute.tv_sec
  91           && current.current.tv_nsec >= deadline.absolute.tv_nsec))
  92     return 0;
  93   time_t sec = deadline.absolute.tv_sec - current.current.tv_sec;
  94   if (sec >= INT_MAX)
  95     /* This value will overflow below.  */
  96     return INT_MAX;
  97   int nsec = deadline.absolute.tv_nsec - current.current.tv_nsec;
  98   if (nsec < 0)
  99     {
 100       /* Borrow from the seconds field.  */
 101       assert (sec > 0);
 102       --sec;
 103       nsec += 1000 * 1000 * 1000;
 104     }
 105
 106   /* Prepare for rounding up to milliseconds.  */
 107   nsec += 999999;
 108   if (nsec > 1000 * 1000 * 1000)
 109     {
 110       assert (sec < INT_MAX);
 111       ++sec;
 112       nsec -= 1000 * 1000 * 1000;
 113     }
 114
 115   unsigned int msec = nsec / (1000 * 1000);
 116   if (sec > INT_MAX / 1000)
 117     return INT_MAX;
 118   msec += sec * 1000;
 119   if (msec > INT_MAX)
 120     return INT_MAX;
 121   return msec;
 122 }