Speed test for context switch timers

context_switch_timer.cc

#include <sched.h>
#include <sys/time.h>
#include <signal.h>
#include <pthread.h>

#include <cstdint>
#include <cstdlib>

#include <iostream>


#define NUM_THREADS 20


namespace {

pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

volatile long switches = 0L;
long msec = 0L;

/**
 * Current GMT time in ms since the Epoch
 */
uint64_t epochmsec() {
 timeval tv = timeval();
 if (gettimeofday(&tv, 0) == 0) {
   return tv.tv_sec * 1000 + tv.tv_usec / 1000;
 }
 else {
   return 0L;
 }
}

/**
 * ALRM signal handler, logs context switching statistics
 */
void alarm_handler(int signum) {
 alarm(1);
 uint64_t tm = epochmsec();
 uint64_t delta = tm - msec;
 msec = tm;
 std::cout << (delta / (double) switches * 1000) << "ns" << std::endl;
 switches = 0;
}

/**
 * Thread function
 */
void* thread_func(void* arg) {
 for(;;) {
   pthread_mutex_lock(&mtx);
   ++switches;
   pthread_mutex_unlock(&mtx);
   sched_yield();
 }
}

} // namespace

int main() {
 msec = epochmsec();

 pthread_t threads[NUM_THREADS];

 for (size_t i = 0; i < sizeof threads; ++i) {
   pthread_create(&threads[i], 0, &thread_func, 0);
 }

 // setup an alarm to print log message every second
 signal(SIGALRM, &alarm_handler);
 alarm(1);

 for (;;) {
   sleep(1000);
 }

 return 0;
}