gettime.cc

   1 /*
   2  * Copyright (c), MM Weiss
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without modification,
   6  * are permitted provided that the following conditions are met:
   7  *
   8  *     1. Redistributions of source code must retain the above copyright notice,
   9  *     this list of conditions and the following disclaimer.
  10  *
  11  *     2. Redistributions in binary form must reproduce the above copyright notice,
  12  *     this list of conditions and the following disclaimer in the documentation
  13  *     and/or other materials provided with the distribution.
  14  *
  15  *     3. Neither the name of the MM Weiss nor the names of its contributors
  16  *     may be used to endorse or promote products derived from this software without
  17  *     specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  20  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  21  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
  22  * SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
  24  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
  26  * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
  27  * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28  */
  29
  30 /*
  31  *  clock_gettime_stub.c
  32  *  gcc -Wall -c clock_gettime_stub.c
  33  *  posix realtime functions; MacOS user space glue
  34  */
  35
  36 /*  @comment
  37  *  other possible implementation using intel builtin rdtsc
  38  *  rdtsc-workaround: http://www.mcs.anl.gov/~kazutomo/rdtsc.html
  39  *
  40  *  we could get the ticks by doing this
  41  *
  42  *  __asm __volatile("mov %%ebx, %%esi\n\t"
  43  *              "cpuid\n\t"
  44  *              "xchg %%esi, %%ebx\n\t"
  45  *              "rdtsc"
  46  *              : "=a" (a),
  47  *                "=d" (d)
  48  *      );
  49
  50  *  we could even replace our tricky sched_yield call by assembly code to get a better accurency,
  51  *  anyway the following C stub will satisfy 99% of apps using posix clock_gettime call,
  52  *  moreover, the setter version (clock_settime) could be easly written using mach primitives:
  53  *  http://www.opensource.apple.com/source/xnu/xnu-${VERSION}/osfmk/man/ (clock_[set|get]_time)
  54  *
  55  *  hackers don't be crackers, don't you use a flush toilet?
  56  *
  57  *
  58  *  @see draft: ./posix-realtime-stub/posix-realtime-stub.c
  59  *
  60  */
  61
  62
  63 #ifdef __APPLE__
  64
  65 #pragma weak clock_gettime
  66
  67 #include <sys/time.h>
  68 #include <sys/resource.h>
  69 #include <mach/mach.h>
  70 #include <mach/clock.h>
  71 #include <mach/mach_time.h>
  72 #include <errno.h>
  73 #include <unistd.h>
  74 #include <sched.h>
  75
  76 typedef enum {
  77         CLOCK_REALTIME,
  78         CLOCK_MONOTONIC,
  79         CLOCK_PROCESS_CPUTIME_ID,
  80         CLOCK_THREAD_CPUTIME_ID
  81 } clockid_t;
  82
  83 static mach_timebase_info_data_t __clock_gettime_inf;
  84
  85 int clock_gettime(clockid_t clk_id, struct timespec *tp) {
  86         kern_return_t   ret;
  87         clock_serv_t    clk;
  88         clock_id_t clk_serv_id;
  89         mach_timespec_t tm;
  90
  91         uint64_t start, end, delta, nano;
  92
  93         int retval = -1;
  94         switch (clk_id) {
  95                 case CLOCK_REALTIME:
  96                 case CLOCK_MONOTONIC:
  97                         clk_serv_id = clk_id == CLOCK_REALTIME ? CALENDAR_CLOCK : SYSTEM_CLOCK;
  98                         if (KERN_SUCCESS == (ret = host_get_clock_service(mach_host_self(), clk_serv_id, &clk))) {
  99                                 if (KERN_SUCCESS == (ret = clock_get_time(clk, &tm))) {
 100                                         tp->tv_sec  = tm.tv_sec;
 101                                         tp->tv_nsec = tm.tv_nsec;
 102                                         retval = 0;
 103                                 }
 104                         }
 105                         if (KERN_SUCCESS != ret) {
 106                                 errno = EINVAL;
 107                                 retval = -1;
 108                         }
 109                 break;
 110                 case CLOCK_PROCESS_CPUTIME_ID:
 111                 case CLOCK_THREAD_CPUTIME_ID:
 112                         start = mach_absolute_time();
 113                         if (clk_id == CLOCK_PROCESS_CPUTIME_ID) {
 114                                 getpid();
 115                         } else {
 116                                 sched_yield();
 117                         }
 118                         end = mach_absolute_time();
 119                         delta = end - start;
 120                         if (0 == __clock_gettime_inf.denom) {
 121                                 mach_timebase_info(&__clock_gettime_inf);
 122                         }
 123                         nano = delta * __clock_gettime_inf.numer / __clock_gettime_inf.denom;
 124                         tp->tv_sec = nano * 1e-9;
 125                         tp->tv_nsec = nano - (tp->tv_sec * 1e9);
 126                         retval = 0;
 127                 break;
 128                 default:
 129                         errno = EINVAL;
 130                         retval = -1;
 131         }
 132         return retval;
 133 }
 134
 135 #endif // __APPLE__