2010_01_08_spin_lock.md

[pthread] 同步机制(5) -- spin lock (REALTIME)

最后一个同步机制，spinlock (自旋锁)。spinlock 用法与 mutex 类似，但 spinlock 在 block 时是 busy wait。

这可通过 top 明显看到。

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

pthread_spinlock_t global_sl;

void *mythr(void *arg)
{
    int n = (int)arg;
    pthread_spin_lock(&global_sl);
    printf("thr #%d lock, time = %d\n", n, time(NULL));
    sleep(2);
    pthread_spin_unlock(&global_sl);
    return (void *)0;
}

int main()
{
    pthread_t pid1, pid2;
    pthread_spin_init(&global_sl, PTHREAD_PROCESS_PRIVATE);

    pthread_create(&pid1, NULL, mythr, (void *)1);
    pthread_create(&pid2, NULL, mythr, (void *)2);
    
    pthread_join(pid1, NULL);
    pthread_join(pid2, NULL);

    pthread_spin_destroy(&global_sl);
    return 0;
}

$ ./a.out 
thr #1 lock, time = 1262961184
thr #2 lock, time = 1262961186