临界区执行时间长的情况下，spin_lock 执行效率低于 mutex_lock

spinvsmutex2.c

//Name: spinvsmutex2.c
//http://www.parallellabs.com/2010/01/31/pthreads-programming-spin-lock-vs-mutex-performance-analysis/
//Source: http://www.solarisinternals.com/wiki/index.php/DTrace_Topics_Locks
//Compile(spin lock version): gcc -o spin -DUSE_SPINLOCK spinvsmutex2.c -lpthread
//Compile(mutex version): gcc -o mutex spinvsmutex2.c -lpthread
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/syscall.h>

#define THREAD_NUM 2

pthread_t g_thread[THREAD_NUM];
#ifdef USE_SPINLOCK
pthread_spinlock_t g_spin;
#else
pthread_mutex_t g_mutex;
#endif
__uint64_t g_count;

pid_t gettid()
{
	return syscall(SYS_gettid);
}

void *run_amuck(void *arg)
{
	int i, j;

	printf("Thread %lu started.\n", (unsigned long)gettid());

	for (i = 0; i < 1000; i++) {
#ifdef USE_SPINLOCK
		pthread_spin_lock(&g_spin);
#else
		pthread_mutex_lock(&g_mutex);
#endif
		for (j = 0; j < 10000000; j++) {
			if (g_count++ == 123456789)
				printf("Thread %lu wins!\n", (unsigned long)gettid());
		}
#ifdef USE_SPINLOCK
		pthread_spin_unlock(&g_spin);
#else
		pthread_mutex_unlock(&g_mutex);
#endif
	}

	printf("Thread %lu finished!\n", (unsigned long)gettid());

	return (NULL);
}

int main(int argc, char *argv[])
{
	int i, threads = THREAD_NUM;

	printf("Creating %d threads...\n", threads);
#ifdef USE_SPINLOCK
	pthread_spin_init(&g_spin, 0);
#else
	pthread_mutex_init(&g_mutex, NULL);
#endif
	for (i = 0; i < threads; i++)
		pthread_create(&g_thread[i], NULL, run_amuck, (void *) i);

	for (i = 0; i < threads; i++)
		pthread_join(g_thread[i], NULL);

	printf("Done.\n");

	return (0);
}

并发下的单例模式：
http://blog.csdn.net/cselmu9/article/details/51366946