/*
 
 File: benchmark.c of Dispatch_Compared
 
 Abstract: Compare overhead of several GCD approaches with that of serial code and threads
 
 Version: 1.0
 
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*/

#include "benchmark.h"

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <locale.h>

#include <math.h>  
#include <sys/sysctl.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <mach/mach_time.h>  

#include <dispatch/dispatch.h>

static int64_t offset_nsec = 1e6;  // start at 1 msec for warmup purposes
static int test_running = 0;

// set from $ sysctl hw.cpufrequency
void show_cpu_speed(void)
{
    double cpu_speed = 0.0;
    unsigned hertz;
	size_t size = sizeof(unsigned);
	int mib[2] = {CTL_HW, HW_CPU_FREQ};
	sysctl(mib, 2, &hertz, &size, NULL, 0);
    cpu_speed = hertz / 1.0e9;
	printf("CPU speed: %.2lf GHz\n", cpu_speed);
}

void show_locale(void)
{
    char *lang = getenv("LANG");
    setlocale(LC_NUMERIC, (lang != NULL) ? lang : "en_US.utf-8");
#ifdef DEBUG
	printf("Locale: %s\n", setlocale(LC_NUMERIC, NULL));  
#endif
}

void benchmark_setup(int test_seconds)
{
    offset_nsec = test_seconds * NSEC_PER_SEC;
    show_locale();
    show_cpu_speed();
}

void benchmark_begin()
{
    dispatch_time_t duration = dispatch_walltime(DISPATCH_TIME_NOW, offset_nsec);
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
    dispatch_after(duration, queue, ^{
        test_running = 0;
    });
    test_running = 1;    
}

int benchmark_running()
{
    return test_running;
}


typedef struct bench_times {
    double wall;
    double wall_sq;
    double user;
    double system;
} bench_times_t;

double resource_usec(struct timeval *time) {
    return time->tv_sec*1e6 + time->tv_usec;
}

void bench_start(bench_times_t *now)
{
    static double usec_per_unit = 0.0;
    if (0 == usec_per_unit) {
        mach_timebase_info_data_t sTimebaseInfo;
        mach_timebase_info(&sTimebaseInfo);
        double nsec_per_unit = sTimebaseInfo.numer / sTimebaseInfo.denom;
        usec_per_unit = nsec_per_unit / 1e3;
    }
    struct rusage resource_times;
    getrusage(RUSAGE_SELF, &resource_times);
    
    now->wall = mach_absolute_time() * usec_per_unit;
    now->wall_sq = 0;
    now->user = resource_usec(&resource_times.ru_utime);
    now->system = resource_usec(&resource_times.ru_stime);
}

void bench_stop(bench_times_t *then)
{
    bench_times_t now;
    bench_start(&now);
    
    then->wall    = (now.wall - then->wall);
    then->wall_sq = then->wall * then->wall;
    then->user    = (now.user - then->user);
    then->system  = (now.system - then->system);
}

void bench_set(bench_times_t *dest, bench_times_t *src)
{
    dest->wall    = src->wall;
    dest->wall_sq = src->wall_sq;
    dest->user    = src->user;
    dest->system  = src->system;
}

void bench_add(bench_times_t *dest, bench_times_t *src)
{
    dest->wall    += src->wall;
    dest->wall_sq += src->wall_sq;
    dest->user    += src->user;
    dest->system  += src->system;
}

void bench_normalize(bench_times_t *dest, int n)
{
    dest->wall    /= n;
    dest->wall_sq /= n;
    dest->user    /= n;
    dest->system  /= n;
}


void benchmark_header(int i)
{
    printf("\n  µsecs±error/%-'8d = WALL(µs)±error   [+-rate]   USER (µs) +    SYS (µs) [overhead]\n",i);
}

void benchmark_function(int n, char *label, void* (*f)(int), void (*cleanup)(int, void*))
{
    static bench_times_t base = { 0, 0, 0 };
    bench_times_t timer = { 0, 0, 0 };
    int count = 0;

    void *ptr = f(n); //warmup
    if (NULL != cleanup) cleanup(n, ptr);

    benchmark_begin();
    while (benchmark_running()) {
        ++count;        
        bench_times_t lap_timer;
        bench_start(&lap_timer);
        ptr = f(n);
        bench_stop(&lap_timer);
        bench_add(&timer, &lap_timer);
        if (NULL != cleanup) cleanup(n, ptr);
    } 
    bench_normalize(&timer, count);
    
    if (0 == strncmp(label, "loop", 8) || 0 == strncmp(label, "alloc", 8) || 0 == base.wall) {
        bench_set(&base, &timer);
    }
    double wall_error = sqrt(timer.wall_sq - timer.wall*timer.wall);
    double speedup = base.wall/timer.wall; // note: inverted vis-a-vis overhead
    double overhead = (timer.user + timer.system) / (base.user + base.system);
    
	printf("%7.3f±%'5.3f/%-8s = %'8.3g±%'-7.2g [%+5.0f%%] %'10.4gu + %'10.4gs [%7.0f%%]\n",
           timer.wall / n, wall_error / n, label, 
           timer.wall, wall_error, (speedup-1)*100,
           timer.user, timer.system, (overhead-1)*100);
}