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