gettime.cc

/*
 * Copyright (c), MM Weiss
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, 
 * are permitted provided that the following conditions are met:
 * 
 *     1. Redistributions of source code must retain the above copyright notice, 
 *     this list of conditions and the following disclaimer.
 *     
 *     2. Redistributions in binary form must reproduce the above copyright notice, 
 *     this list of conditions and the following disclaimer in the documentation 
 *     and/or other materials provided with the distribution.
 *     
 *     3. Neither the name of the MM Weiss nor the names of its contributors 
 *     may be used to endorse or promote products derived from this software without 
 *     specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
 * SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR 
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 *  clock_gettime_stub.c
 *  gcc -Wall -c clock_gettime_stub.c
 *  posix realtime functions; MacOS user space glue
 */
 
/*  @comment
 *  other possible implementation using intel builtin rdtsc
 *  rdtsc-workaround: http://www.mcs.anl.gov/~kazutomo/rdtsc.html
 *  
 *  we could get the ticks by doing this
 * 
 *  __asm __volatile("mov %%ebx, %%esi\n\t"
 *  		"cpuid\n\t"
 *  		"xchg %%esi, %%ebx\n\t"
 *  		"rdtsc"
 *  		: "=a" (a),
 *  		  "=d" (d)
 * 	);
 
 *  we could even replace our tricky sched_yield call by assembly code to get a better accurency,
 *  anyway the following C stub will satisfy 99% of apps using posix clock_gettime call, 
 *  moreover, the setter version (clock_settime) could be easly written using mach primitives:
 *  http://www.opensource.apple.com/source/xnu/xnu-${VERSION}/osfmk/man/ (clock_[set|get]_time)
 *  
 *  hackers don't be crackers, don't you use a flush toilet?
 * 
 *
 *  @see draft: ./posix-realtime-stub/posix-realtime-stub.c
 *
 */
 

#ifdef __APPLE__

#pragma weak clock_gettime

#include <sys/time.h>
#include <sys/resource.h>
#include <mach/mach.h>
#include <mach/clock.h>
#include <mach/mach_time.h>
#include <errno.h>
#include <unistd.h>
#include <sched.h>

typedef enum {
	CLOCK_REALTIME,
	CLOCK_MONOTONIC,
	CLOCK_PROCESS_CPUTIME_ID,
	CLOCK_THREAD_CPUTIME_ID
} clockid_t;

static mach_timebase_info_data_t __clock_gettime_inf;

int clock_gettime(clockid_t clk_id, struct timespec *tp) {
	kern_return_t   ret;
	clock_serv_t    clk;
	clock_id_t clk_serv_id;
	mach_timespec_t tm;
	
	uint64_t start, end, delta, nano;
	
	task_basic_info_data_t tinfo;
	task_thread_times_info_data_t ttinfo;
	mach_msg_type_number_t tflag;
	
	int retval = -1;
	switch (clk_id) {
		case CLOCK_REALTIME:
		case CLOCK_MONOTONIC:
			clk_serv_id = clk_id == CLOCK_REALTIME ? CALENDAR_CLOCK : SYSTEM_CLOCK;
			if (KERN_SUCCESS == (ret = host_get_clock_service(mach_host_self(), clk_serv_id, &clk))) {
				if (KERN_SUCCESS == (ret = clock_get_time(clk, &tm))) {
					tp->tv_sec  = tm.tv_sec;
					tp->tv_nsec = tm.tv_nsec;
					retval = 0;
				}
			}
			if (KERN_SUCCESS != ret) {
				errno = EINVAL;
				retval = -1;
			}
		break;
		case CLOCK_PROCESS_CPUTIME_ID:
		case CLOCK_THREAD_CPUTIME_ID:
			start = mach_absolute_time();
			if (clk_id == CLOCK_PROCESS_CPUTIME_ID) {
				getpid();
			} else {
				sched_yield();
			}
			end = mach_absolute_time();
			delta = end - start;	
			if (0 == __clock_gettime_inf.denom) {
				mach_timebase_info(&__clock_gettime_inf);
			}
			nano = delta * __clock_gettime_inf.numer / __clock_gettime_inf.denom;
			tp->tv_sec = nano * 1e-9;  
			tp->tv_nsec = nano - (tp->tv_sec * 1e9);
			retval = 0;
		break;
		default:
			errno = EINVAL;
			retval = -1;
	}
	return retval;
}

#endif // __APPLE__