Linux多线程实现及线程同步函数分析

Posted 2020-10-15 *平凡*随风舞

在Linux中，多线程的本质仍是进程，它与进程的区别：

进程：独立地址空间，拥有PCB

线程：也有PCB，但没有独立的地址空间（共享）

线程的特点：

1，线程是轻量级进程，有PCB，创建线程使用的底层函数和进程一样，都是clone

2，从内核看进程和线程是一样的，都有各自不同的PCB

3，进程可以蜕变成线程

4，在LINUX中，线程是最小的执行单位，进程是最小的分配资源单位

查看指定线程的LWP号命令：

ps -Lf pid

线程优点：

提高程序并发性

开销小

数据通信，共享数据方便

线程缺点：

库函数 ，不稳定

调试，编写困难，GDB

对信号支持不好

 

线程属性，可以在一开始就设置好分离态，具体在下面的代码有说明！

线程同步，主要有互斥锁mutex，读写锁，条件变量，信号量

 

 

线程创建函数原型：

int pthread_create(
    pthread_t *thread,  				// 线程ID
    const pthread_attr_t *attr, 		// 线程属性
    void *(*start_routine) (void *), 	// 线程主函数
    void *arg							// 主函数参数
);

　　粘上基本创建线程模型：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>

//函数回调
void *mythread(void *args)
{
	printf("child thread id==[%ld]\n", pthread_self());
}

int main()
{
	pthread_t thread;
	
	//创建一个线程
	int ret = pthread_create(&thread, NULL, mythread, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret)); 
		return -1;
	}

	printf("main thread id==[%ld]\n", pthread_self());
	sleep(1);
}

　　线程属性，在创建时分离代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>

void *mythread(void *args)
{
	printf("child thread id==[%ld]\n", pthread_self());
}

int main()
{
	pthread_t thread;
	//线程属性
	pthread_attr_t attr;

	//线程属性初始化
	pthread_attr_init(&attr);
	//设置线程到分离属性
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
	
	//创建一个线程
	int ret = pthread_create(&thread, &attr, mythread, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret)); 
		return -1;
	}

	printf("main thread id==[%ld]\n", pthread_self());
	sleep(1);
	
	ret = pthread_join(thread, NULL);
	if(ret!=0)
	{
		printf("pthread_join error, [%s]\n", strerror(ret));
	}

	//释放线程属性
	pthread_attr_destroy(&attr);

	return 0;
}

　　互斥锁实现代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <time.h>

//定义一把锁
pthread_mutex_t mutex;

void *mythread1(void *args)
{
	while(1)
	{
		//加锁
		pthread_mutex_lock(&mutex);
		pthread_mutex_lock(&mutex);

		printf("hello ");
		sleep(rand()%3);
		printf("world\n");
	
		//解锁
		pthread_mutex_unlock(&mutex);
		sleep(rand()%3);
	}

	pthread_exit(NULL);
}


void *mythread2(void *args)
{
	while(1)
	{
		//加锁
		pthread_mutex_lock(&mutex);

		printf("HELLO ");
		sleep(rand()%3);
		printf("WORLD\n");

		//解锁
		pthread_mutex_unlock(&mutex);
		sleep(rand()%3);
	}

	pthread_exit(NULL);
}

int main()
{
	int ret;
	pthread_t thread1;
	pthread_t thread2;

	//随机数种子
	srand(time(NULL));
	
	//互斥锁初始化
	pthread_mutex_init(&mutex, NULL);

	ret = pthread_create(&thread1, NULL, mythread1, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}
	
	ret = pthread_create(&thread2, NULL, mythread2, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}

	//等待线程结束
	pthread_join(thread1, NULL);
	pthread_join(thread2, NULL);

	//释放互斥锁
	pthread_mutex_destroy(&mutex);
	return 0;
}

　　读写锁代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>

int number = 0;

//定义一把读写锁
pthread_rwlock_t rwlock;

void *fun_write(void *args)
{
	int i = *(int *)args;
	int n;
	while(1)
	{
		//加写锁
		pthread_rwlock_wrlock(&rwlock);

		n = number;
		n++;
		//sleep(rand()%3);
		number = n;		
		printf("W->[%d]:[%d]\n", i, number);

		//解写锁
		pthread_rwlock_unlock(&rwlock);
		sleep(rand()%3);
	}

	pthread_exit(NULL);
}

void *fun_read(void *args)
{
	int i = *(int *)args;
	while(1)
	{
		//加读锁
		pthread_rwlock_rdlock(&rwlock);

		printf("R->[%d]:[%d]\n", i, number);	

		//解锁
		pthread_rwlock_unlock(&rwlock);
		sleep(rand()%3);
	}

	pthread_exit(NULL);
}

int main()
{
	int i;
	int ret;
	int n = 8;
	int arr[8];
	pthread_t thread[8];

	//读写锁初始化
	pthread_rwlock_init(&rwlock, NULL);

	//创建3个写线程
	for(i=0; i<3; i++)
	{
		arr[i] = i;
		ret = pthread_create(&thread[i], NULL, fun_write, (void *)&arr[i]);
		if(ret!=0)
		{
			printf("pthread_create error, [%s]\n", strerror(ret));
			return -1;
		}
	}
	
	//创建5个读线程
	for(i=3; i<n; i++)
	{
		arr[i] = i;
		ret = pthread_create(&thread[i], NULL, fun_read, (void *)&arr[i]);
		if(ret!=0)
		{
			printf("pthread_create error, [%s]\n", strerror(ret));
			return -1;
		}
	}


	for(i=0; i<n; i++)
	{
		//回收子线程
		pthread_join(thread[i], NULL);
	}

	//释放读写锁资源
	pthread_rwlock_destroy(&rwlock);

	return 0;
}

　　cond条件变量代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>

typedef struct node
{
	int data;
	struct node *next;
}NODE;

//链表头节点指针
NODE *head = NULL;

//互斥锁
pthread_mutex_t mutex;

//条件变量
pthread_cond_t cond;

//生产者线程处理函数
void *producer(void *args)
{
	NODE *pNode = NULL;	

	while(1)
	{
		pNode = (NODE *)malloc(sizeof(NODE));		
		if(pNode==NULL)
		{
			perror("malloc error\n");
			exit(1);
		}
		pNode->data = rand()%1000;

		//lock共享资源 
		pthread_mutex_lock(&mutex);

		pNode->next = head;
		head=pNode;
		printf("P:[%d]\n", head->data);
		
		//对共享资源解锁
		pthread_mutex_unlock(&mutex);
		
		//使用条件变量解除对线程到阻塞
		pthread_cond_signal(&cond);
		
		sleep(rand()%3);	
	}
}

//消费者线程处理函数
void *consumer(void *args)
{
	NODE *pNode = NULL;
	while(1)
	{
		//lock共享资源 
		pthread_mutex_lock(&mutex);

		if(head==NULL)
		{
			//条件不满足阻塞等待head不为空
			pthread_cond_wait(&cond, &mutex);
		}

		printf("C:[%d]\n", head->data);	
		pNode = head;
		head = head->next;

		//对共享资源解锁
		pthread_mutex_unlock(&mutex);

		free(pNode);
		pNode = NULL;

		sleep(rand()%3);	
	}
}

int main(int argc, char *argv[])
{
	int ret;
	pthread_t thread1;
	pthread_t thread2;
	pthread_mutex_t mutex;
	pthread_cond_t cond;

	//初始化互斥锁
	pthread_mutex_init(&mutex, NULL);

	//初始化条件变量
	pthread_cond_init(&cond, NULL);

	//创建生产者线程
	ret = pthread_create(&thread1, NULL, producer, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}

	//创建消费者线程
	ret = pthread_create(&thread2, NULL, consumer, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}

	//主线程回收子线程
	pthread_join(thread1, NULL);	
	pthread_join(thread2, NULL);	

	//释放锁资源
	pthread_mutex_destroy(&mutex);

	//释放条件变量资源
	pthread_cond_destroy(&cond);

	return 0;
}

　　信号量，经典消费者生产者模型：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

typedef struct node
{
	int data;
	struct node *next;
}NODE;

//链表头节点指针
NODE *head = NULL;

sem_t sem_consumer;
sem_t sem_producer;

//生产者线程处理函数
void *producer(void *args)
{
	NODE *pNode = NULL;	

	while(1)
	{
		pNode = (NODE *)malloc(sizeof(NODE));		
		if(pNode==NULL)
		{
			perror("malloc error\n");
			exit(1);
		}
		pNode->data = rand()%1000;

		//sem_producer--, 若为0则阻塞
		sem_wait(&sem_producer);

		pNode->next = head;
		head=pNode;
		printf("P:[%d]\n", head->data);
		
		//sem_consumer++
		sem_post(&sem_consumer);

		sleep(rand()%3);	
	}
}

//消费者线程处理函数
void *consumer(void *args)
{
	NODE *pNode = NULL;
	while(1)
	{
		//sem_consumer--, 若为0则阻塞
		sem_wait(&sem_consumer);
		
		printf("C:[%d]\n", head->data);	
		pNode = head;
		head = head->next;

		//sem_producer++
		sem_post(&sem_producer);

		free(pNode);
		pNode = NULL;

		sleep(rand()%3);	
	}
}

int main(int argc, char *argv[])
{
	int ret;
	pthread_t thread1;
	pthread_t thread2;

	//信号量初始化
	sem_init(&sem_producer, 0, 5);
	sem_init(&sem_consumer, 0, 0);

	//创建生产者线程
	ret = pthread_create(&thread1, NULL, producer, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}

	//创建消费者线程
	ret = pthread_create(&thread2, NULL, consumer, NULL);
	if(ret!=0)
	{
		printf("pthread_create error, [%s]\n", strerror(ret));
		return -1;
	}

	//主线程回收子线程
	pthread_join(thread1, NULL);	
	pthread_join(thread2, NULL);	

	//释放信号量资源
	sem_destroy(&sem_producer);
	sem_destroy(&sem_consumer);

	return 0;
}