Linux多线程实现及线程同步函数分析
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;
}
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