#include <time.h>
#include <stdio.h>
#include <pthread.h>
#include <features.h>

// compile command line
// gcc pthread_concurrency.c -D_GNU_SOURCE  -o pthread_concurrency -lpthread -lrt

struct timespec diff_timespec(struct timespec start, struct timespec end);
long long millisec_elapsed(struct timespec diff);

#define FIFTY_MILLION 50000000

int main(int argc, char** argv)
{
    struct timespec start;
    struct timespec end;
    struct timespec diff;
    int i;

    pthread_mutex_t mutex;
    pthread_mutex_init(&mutex, NULL);
    
    pthread_rwlock_t rwlock;
    pthread_rwlock_init(&rwlock, NULL);

    pthread_spinlock_t spinlock;
    pthread_spin_init(&spinlock, 0);

    // TEST speed of mutex //////////////////////////////////////////
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 0 ; i < FIFTY_MILLION; ++i)
    {
        pthread_mutex_lock(&mutex);
        pthread_mutex_unlock(&mutex);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("mutex took %lld milliseconds\n", millisec_elapsed(diff));
    /////////////////////////////////////////////////////////////////

    // TEST speed of read lock //////////////////////////////////////////
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 0 ; i < FIFTY_MILLION; ++i)
    {
        pthread_rwlock_rdlock(&rwlock);
        pthread_rwlock_unlock(&rwlock);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("read lock took %lld milliseconds\n", millisec_elapsed(diff));
    /////////////////////////////////////////////////////////////////

    // TEST speed of write lock //////////////////////////////////////////
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 0 ; i < FIFTY_MILLION; ++i)
    {
        pthread_rwlock_wrlock(&rwlock);
        pthread_rwlock_unlock(&rwlock);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("write lock took %lld milliseconds\n", millisec_elapsed(diff));
    /////////////////////////////////////////////////////////////////

    // TEST speed of spin lock //////////////////////////////////////////
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 0 ; i < FIFTY_MILLION; ++i)
    {
        pthread_spin_lock(&spinlock);
        pthread_spin_unlock(&spinlock);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("spin lock took %lld milliseconds\n", millisec_elapsed(diff));
    /////////////////////////////////////////////////////////////////

    pthread_mutex_destroy(&mutex);
    pthread_rwlock_destroy(&rwlock);
    pthread_spin_destroy(&spinlock);

    return 0;
}

struct timespec diff_timespec(struct timespec start, struct timespec end)
{
    struct timespec result;

    if (end.tv_nsec < start.tv_nsec){ // peform carry like in normal subtraction
        //                123456789
        result.tv_nsec = 1000000000 + end.tv_nsec - start.tv_nsec;        
        result.tv_sec = end.tv_sec - 1 - start.tv_sec;
    }
    else{
        result.tv_nsec = end.tv_nsec - start.tv_nsec;        
        result.tv_sec = end.tv_sec - start.tv_sec;
    }

    return result;
}

long long millisec_elapsed(struct timespec diff){
    //                                123                     123456
    return ((long long)diff.tv_sec * 1000) + (diff.tv_nsec / 1000000);
}