cas_counter.c

// 这个counter是线程安全的, 使用了 CAS 指令
#include <stdio.h>
#include <pthread.h>

volatile int counter = 0;

void counter_inc()
{
	int observed;
	do {
		observed = counter;
	} while(!__sync_bool_compare_and_swap(&counter, observed, observed + 1));

}

void* thread_main(void* p)
{
	int i;
	for(i = 0; i < 100000000; i ++)
		if(i % 2 == 0) counter_inc();
	return NULL;
}
#define N 4
int main()
{
	pthread_t t[N];
	int i;
	for(i = 0; i < N; i ++)
		pthread_create(&t[i], NULL, thread_main, NULL);

	for(i = 0; i < N; i ++)
		pthread_join(t[i], NULL);

	printf("%d\n", counter);

	return 0;
}

incl_counter.c

// 这个counter在单核CPU上是线程安全的, 使用了 incl 指令
#include <stdio.h>
#include <pthread.h>

volatile int counter = 0;

void counter_inc()
{
	asm volatile ("incl %1" : "=m" (counter) : "m" (counter)); 
}

void* thread_main(void* p)
{
	int i;
	for(i = 0; i < 100000000; i ++)
		if(i % 2 == 0) counter_inc();
	return NULL;
}
#define N 4
int main()
{
	pthread_t t[N];
	int i;
	for(i = 0; i < N; i ++)
		pthread_create(&t[i], NULL, thread_main, NULL);

	for(i = 0; i < N; i ++)
		pthread_join(t[i], NULL);

	printf("%d\n", counter);

	return 0;
}

lock_incl_counter.c

// 这个counter是线程安全的, 使用了 lock incl 指令
#include <stdio.h>
#include <pthread.h>

volatile int counter = 0;

void counter_inc()
{
	asm volatile ("lock incl %1" : "=m" (counter) : "m" (counter)); 
}

void* thread_main(void* p)
{
	int i;
	for(i = 0; i < 100000000; i ++)
		if(i % 2 == 0) counter_inc();
	return NULL;
}
#define N 4
int main()
{
	pthread_t t[N];
	int i;
	for(i = 0; i < N; i ++)
		pthread_create(&t[i], NULL, thread_main, NULL);

	for(i = 0; i < N; i ++)
		pthread_join(t[i], NULL);

	printf("%d\n", counter);

	return 0;
}

mutex_counter.c

// 这个counter是线程安全的, 使用了pthread_mutex

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

volatile int counter = 0;

pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;

void counter_inc()
{
	pthread_mutex_lock(&mut);
	counter ++;
	pthread_mutex_unlock(&mut);
}

void* thread_main(void* p)
{
	int i;
	for(i = 0; i < 100000000; i ++)
		if(i % 2 == 0) counter_inc();
	return NULL;
}
#define N 4
int main()
{
	pthread_t t[N];
	int i;
	for(i = 0; i < N; i ++)
		pthread_create(&t[i], NULL, thread_main, NULL);

	for(i = 0; i < N; i ++)
		pthread_join(t[i], NULL);

	printf("%d\n", counter);

	return 0;
}