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4d78336 Apr 7, 2016
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// Copyright (C) 2010 Benoit Sigoure
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
#include <pthread.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/syscall.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
#include <linux/futex.h>
static inline long long unsigned time_ns(struct timespec* const ts) {
if (clock_gettime(CLOCK_REALTIME, ts)) {
exit(1);
}
return ((long long unsigned) ts->tv_sec) * 1000000000LLU
+ (long long unsigned) ts->tv_nsec;
}
static const int iterations = 500000;
static void* thread(void* restrict ftx) {
int* futex = (int*) ftx;
for (int i = 0; i < iterations; i++) {
sched_yield();
while (syscall(SYS_futex, futex, FUTEX_WAIT, 0xA, NULL, NULL, 42)) {
// retry
sched_yield();
}
*futex = 0xB;
while (!syscall(SYS_futex, futex, FUTEX_WAKE, 1, NULL, NULL, 42)) {
// retry
sched_yield();
}
}
return NULL;
}
int main(void) {
struct timespec ts;
const int shm_id = shmget(IPC_PRIVATE, sizeof (int), IPC_CREAT | 0666);
int* futex = shmat(shm_id, NULL, 0);
pthread_t thd;
if (pthread_create(&thd, NULL, thread, futex)) {
return 1;
}
*futex = 0xA;
const long long unsigned start_ns = time_ns(&ts);
for (int i = 0; i < iterations; i++) {
*futex = 0xA;
while (!syscall(SYS_futex, futex, FUTEX_WAKE, 1, NULL, NULL, 42)) {
// retry
sched_yield();
}
sched_yield();
while (syscall(SYS_futex, futex, FUTEX_WAIT, 0xB, NULL, NULL, 42)) {
// retry
sched_yield();
}
}
const long long unsigned delta = time_ns(&ts) - start_ns;
const int nswitches = iterations << 2;
printf("%i thread context switches in %lluns (%.1fns/ctxsw)\n",
nswitches, delta, (delta / (float) nswitches));
wait(futex);
return 0;
}