libsyscall/wrappers/mach_timebase_info.c

   1 /*
   2  * Copyright (c) 2016 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23 #include <mach/mach_time.h>
  24
  25 extern kern_return_t
  26 mach_timebase_info_trap(mach_timebase_info_t info);
  27
  28 kern_return_t
  29 mach_timebase_info(mach_timebase_info_t info){
  30     static mach_timebase_info_data_t cached_info;
  31
  32         /*
  33          * This is racy, but because it is safe to initialize twice we avoid a
  34          * barrier in the fast path by risking double initialization.
  35          */
  36     if (cached_info.numer == 0 || cached_info.denom == 0){
  37         kern_return_t kr = mach_timebase_info_trap(&cached_info);
  38         if (kr != KERN_SUCCESS) return kr;
  39     }
  40
  41         info->numer = cached_info.numer;
  42         info->denom = cached_info.denom;
  43
  44     return KERN_SUCCESS;
  45 }