多线程数据安全

//Test01.c

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

int num = 100;

void* thread1_handler(void* param)
{
    while (1)
    {
        ++num;
        printf("Thread1 num=%d\n", num);
    }

}

void* thread2_handler(void* param)
{
    while (1)
    {
        ++num;
        printf("Thread2 num=%d\n", num);
    }
}

void* thread3_handler(void* param)
{
    while (1)
    {
        ++num;
        printf("Thread3 num=%d\n", num);
    }
}

void* thread4_handler(void* param)
{
    while (1)
    {
        ++num;
        printf("Thread4 num=%d\n", num);
    }
}

int main()
{
    pthread_t th1;
    pthread_t th2;
    pthread_t th3;
    pthread_t th4;

    pthread_create(&th1, NULL, thread1_handler, NULL);
    pthread_create(&th2, NULL, thread2_handler, NULL);
    pthread_create(&th3, NULL, thread3_handler, NULL);
    pthread_create(&th4, NULL, thread4_handler, NULL);

    pthread_join(th1, NULL);
    pthread_join(th2, NULL);
    pthread_join(th3, NULL);
    pthread_join(th4, NULL);

printf("Exit!\n");
//while(1);

}

//Test02.c

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

int num = 100;

pthread_mutex_t mutex1;

void* thread1_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        printf("Thread1 num=%d\n", num);
        pthread_mutex_unlock(&mutex1);
    }

}

void* thread2_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        printf("Thread2 num=%d\n", num);
        pthread_mutex_unlock(&mutex1);
    }
}

void* thread3_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        printf("Thread3 num=%d\n", num);
        pthread_mutex_unlock(&mutex1);
    }
}

void* thread4_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        printf("Thread4 num=%d\n", num);
        pthread_mutex_unlock(&mutex1);
    }
}

int main()
{
    pthread_t th1;
    pthread_t th2;
    pthread_t th3;
    pthread_t th4;

    pthread_join(th1, NULL);
    pthread_join(th2, NULL);
    pthread_join(th3, NULL);
    pthread_join(th4, NULL);

printf("Exit!\n");
//while(1);

}

//Test03.c

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

int num = 100;

pthread_mutex_t mutex1;

void* thread1_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        pthread_mutex_unlock(&mutex1);
        printf("Thread1 num=%d\n", num);
    }

}

void* thread2_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        pthread_mutex_unlock(&mutex1);
        printf("Thread2 num=%d\n", num);
    }
}

void* thread3_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        pthread_mutex_unlock(&mutex1);
        printf("Thread3 num=%d\n", num);
    }
}

void* thread4_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        pthread_mutex_unlock(&mutex1);
        printf("Thread4 num=%d\n", num);
    }
}

int main()
{
    pthread_t th1;
    pthread_t th2;
    pthread_t th3;
    pthread_t th4;

    pthread_join(th1, NULL);
    pthread_join(th2, NULL);
    pthread_join(th3, NULL);
    pthread_join(th4, NULL);

printf("Exit!\n");
//while(1);

}

//Test04.c

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

int num = 100;

pthread_mutex_t mutex1;
pthread_mutex_t mutex2;
pthread_mutex_t mutex3;
pthread_mutex_t mutex4;

void* thread1_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex1);
        ++num;
        printf("Thread1 num=%d\n", num);
        pthread_mutex_unlock(&mutex1);
    }

}

void* thread2_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex2);
        ++num;
        printf("Thread2 num=%d\n", num);
        pthread_mutex_unlock(&mutex2);
    }
}

void* thread3_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex3);
        ++num;
        printf("Thread3 num=%d\n", num);
        pthread_mutex_unlock(&mutex3);
    }
}

void* thread4_handler(void* param)
{
    while (1)
    {
        pthread_mutex_lock(&mutex4);
        ++num;
        printf("Thread4 num=%d\n", num);
        pthread_mutex_unlock(&mutex4);
    }
}

int main()
{
    pthread_t th1;
    pthread_t th2;
    pthread_t th3;
    pthread_t th4;

    pthread_join(th1, NULL);
    pthread_join(th2, NULL);
    pthread_join(th3, NULL);
    pthread_join(th4, NULL);

printf("Exit!\n");
//while(1);

}

总结：

只有Test02.c是能保证数据是正常的，即在多线程访问全局变量时，必须对全局变量使用同一把锁，并且把所有对该全局变量的操作放在锁里，即使对全局变量的操作变成原子操作！

posted on 2014-12-24 15:13 张武亮阅读(264) 评论(0) 编辑收藏举报