Linux 多线程 - 线程异步与同步机制

I. 同步机制

线程间的同步机制主要包括三个:

  • 互斥锁
    以排他的方式,防止共享资源被并发访问;
    互斥锁为二元变量, 状态为0-开锁1-上锁;
    开锁必须由上锁的线程执行,不受其它线程干扰.
  • 条件变量
    满足某个特定条件时,可通过条件变量通知其它线程do-something;
    必须与互斥锁*联合使用,单独无法执行.
  • 读写锁
    针对多读者,少写者的情况设定

    • 允许多读,但此时不可写
    • 唯一写,此时不可读.

函数的头文件为:

    #include <phtread.h>     

1. 互斥锁

操作流程:

  • I. 创建互斥锁
  • II. 申请锁:若可用,立刻占用;否则,阻塞等待
  • III. do-something
  • IV. 释放锁
  • V. 销毁锁

以下是互斥锁的基本操作函数:

功能 函数 参数 返回值 说明
初始化锁 int pthread_mutex_init(
pthread_mutex_t *mutex,
const pthread_mutexattr_t *attr)
1. mutex: 欲建立的互斥锁
2.attr:属性,一般为NULL
成功:0
失败:非零值
阻塞申请锁 int pthread_mutex_lock(
pthread_mutex_t *mutex)
mutex:互斥锁 成功:0
失败:非零值
若未申请到,
阻塞等待
非阻塞申请 int pthread_mutex_trylock(
pthread_mutex_t *mutex)
mutex:互斥锁 成功:0
失败:非零值
若未申请到,
返回错误
释放锁 int pthread_mutex_unlock(
pthread_mutex_t *mutex)
mutex:互斥锁 成功:0
失败:非零值
销毁锁 int pthread_mutex_destroy(
pthread_mutex_t *mutex)
mutex:互斥锁 成功:0
失败:非零值

2. 条件变量

注意,条件变量必须与互斥锁共同使用;

以下是条件变量的基本操作函数:

功能 函数 参数 返回值 说明
初始化锁 int pthread_cond_init(
pthread_cond_t *cond,
const pthread_condattr_t *attr)
1. cond: 欲建立的条件变量
2.attr:属性,一般为NULL
成功:0
失败:非零值
等待条件变量 int pthread_cond_wait(
pthread_cond_t *cond,
pthread_mutex_t *mutex)
1.cond:条件变量
2.mutex:互斥锁
成功:0
失败:非零值
阻塞等待
隐含释放申请到的互斥锁
限时等待条件变量 int pthread_cond_timewait(
pthread_cond_t *cond,
pthread_mutex_t *mutex,
const struct timespec *time)
3.time:等待过期的绝对时间
从1970-1-1:0:0:0起
成功:0
失败:非零值
struct timespec{long ts_sec;
long ts_nsec}
单一通知 int pthread_cond_signal(
pthread_cond_t *cond)
cond:条件变量 成功:0
失败:非零值
唤醒等待cond的第一个线程
隐含获取需要的互斥锁
广播通知 int pthread_cond_broadcast(
pthread_cond_t *cond)
cond:条件变量 成功:0
失败:非零值
唤醒所有等待cond的线程
隐含获取需要的互斥锁
销毁条件变量 int pthread_cond_destroy(
pthread_cond_t *cond)
cond:条件变量 成功:0
失败:非零值

3. 读写锁

读写基本原则:

  • 若当前线程读数据,则允许其他线程读数据,但不允许写
  • 若当前线程写数据,则不允许其他线程读、写数据

以下是基本的操作:

功能 函数 参数 返回值 说明
初始化锁 int pthread_rwlock_init(
pthread_rwlock_t *rwlock,
const pthread_rwlockattr_t *attr)
1. rwlock: 欲建立的读写锁
2.attr:属性,一般为NULL
成功:0
失败:非零值
阻塞申请读锁 int pthread_rwlock_rdlock(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值
若未申请到,
阻塞等待
非阻塞申请 int pthread_rwlock_tryrdlock(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值
若未申请到,
返回错误
阻塞申请写锁 int pthread_rwlock_wrlock(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值
若未申请到,
阻塞等待
非阻塞申请写锁 int pthread_rwlock_trywrlock(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值
若未申请到,
返回错误
释放锁 int pthread_mutex_unlock(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值
销毁锁 int pthread_rwlock_destroy(
pthread_rwlock_t *rwlock)
rwlock:读写锁 成功:0
失败:非零值

4. 线程信号量

线程信号量类似进程的信号量,主要是使得多个线程访问共享资源时,顺序互斥访问。
与互斥锁的区别在于:

  • 互斥锁:只有一个bool类型的值,只允许2个线程进行排队;
  • 信号量:允许多个线程共同等待一个共享资源

函数如下:

     #include <semaphore.h>
功能 函数 参数 返回值 说明
创建信号量 int sem_init(sem_t *sem,
int pshared, unsigned int value)
1. sem:信号量地址;
2. pshared:是(!=0)否(0)为共享信号量
3. value:信号量初值
0: 成功
-1: 失败
P操作(阻塞) int sem_wait(sem_t *sem) sem:信号量地址 0: 成功
-1: 失败
P操作(非阻塞) int sem_trywait(sem_t *sem) sem:信号量地址 0: 成功
-1: 失败
P操作(时间) int sem_timedwait(sem_t *sem,
const struct timespec *abs_timeout)
1. sem:信号量地址
2. abs_timeout:超时时间
0: 成功
-1: 失败
struct timespec 见下面
V操作 int sem_post(sem_t *sem) sem:信号量地址 0: 成功
-1: 失败
获取信号量值 int sem_getvalue(sem_t *sem, int *sval) 1. sem:信号量地址
2. sval: 将信号量值放到该地址
0: 成功
-1: 失败
删除信号量 int sem_destroy(sem_t *sem) sem:信号量地址 0: 成功
-1: 失败
struct timespec {
               time_t tv_sec;      /* Seconds */
               long   tv_nsec;     /* Nanoseconds [0 .. 999999999] */
           };

II. 异步机制 - 信号

线程的异步机制只有信号,类似于线程的信号。

线程信号具备以下特点

    1. 任何线程都可以向其它线程(同一进程下)发送信号;
    1. 每个线程都具备自己独立的信号屏蔽集,不影响其它线程;
    1. 线程创建时,不继承原线程的信号屏蔽集;
    1. 同进程下,所有线程共享对某信号的处理方式,即一个设置,所有有效;
    1. 多个线程的程序,向某一个线程发送终止信号,则整个进程终止

信号的基本操作如下:

功能 函数 参数 返回值 说明
安装信号 sighandler_t signal(
int signum,
sighandler_t handler)
1.signum:信号值
2.handler:信号操作
详情参见:
http://www.cnblogs.com/Jimmy1988/p/7575103.html
发送信号 int pthread_kill(
pthread_t threadid,
int signo
1.threadid: 目标线程id
2.signo:信号值
成功:0
失败:非零值
若signo=0,
检测该线程是否存在,
不发送信号
设置屏蔽集 pthread_sigmask(int how,
const sigset_t *set,
sigset_t *oldset)
1.how:如何更改信号掩码
2.newmask:新的信号屏蔽集
3.原信号屏蔽集
成功:0
失败:非零值
how值:
 1.SIG_BLOCK:添加新掩码
 2.SIG_UNBLOCK:删除新掩码
 3.SIG_SETMASK:设置新掩码完全替换旧值

也可以参考这篇博客:https://www.cnblogs.com/coding-my-life/p/4782529.html

III、示例代码

1.同步机制:

1). 互斥锁:

两个线程:

  • 读线程:从stdin中读取数据,并存储
  • 写线程:从存储buffer中读取数据并显示
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>

#define SIZE 128

pthread_mutex_t mutex;
int EXIT = 0;
char word[SIZE];

void * child(void *arg)
{
    while(1)
    {
        while(strlen(word) == 0)
            usleep(100);

        pthread_mutex_lock(&mutex);
        printf("The input words: %s\n", word);
        pthread_mutex_unlock(&mutex);
        if(strcmp("end\n", word) == 0)
        {
            printf("The process end\n");
            EXIT = 1;
            break;
        }
        
        memset(word, '\0', SIZE);
    }
    
    return ;
}

int main()
{
    //1. create the lock
    pthread_mutex_init(&mutex, NULL);
    
    //2.create a new thread
    pthread_t tid;
    pthread_create(&tid, NULL, (void *)*child, NULL);
    
    //3. Input words
    while(EXIT == 0)
    {
        if(strlen(word)!=0)
            usleep(100);
        //add the lock
        else
        {
            pthread_mutex_lock(&mutex);
            printf("Input words:  ");
            fgets(word, SIZE, stdin);
            pthread_mutex_unlock(&mutex);            
        }
    }

    pthread_join(tid, NULL);
    printf("The child has joined\n");
    pthread_mutex_destroy(&mutex);

    return 0;
}

2). 条件变量:

生产者和消费者问题:

  • 生产者:
    向仓库生产数据(大小可任意设定),当满时,阻塞等待仓库有空闲(由消费者消费完后通知)
  • 消费者:
    从仓库读数据,若仓库为空,则阻塞等待,当生产者再次生产产品后通知
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

#define SIZE 2
int Data[SIZE];

typedef struct
{
    pthread_mutex_t lock;
    pthread_cond_t  notFull;
    pthread_cond_t  notEmpty;
    int read_point;
    int write_point;
}sCOND;

sCOND *pCondLock;

void init(void)
{
    //memset(pCondLock, 0, sizeof(sCOND));

    //1.Create a mutex lock
    pthread_mutex_init(&pCondLock->lock, NULL);

    //2.Create two condition variable  
    pthread_cond_init(&pCondLock->notFull, NULL);
    pthread_cond_init(&pCondLock->notEmpty, NULL);

    //set the read and write point 0
    pCondLock->read_point = 0;
    pCondLock->write_point = 0;
}


int put(int data) 
{
    //obtain the mutex lock
    pthread_mutex_lock(&pCondLock->lock);
    
    //check the global variable Data full or not
    while((pCondLock->write_point+1)%SIZE == pCondLock->read_point)
    {
        printf("The buf is full, waitting for not_full signal\n");
        pthread_cond_wait(&pCondLock->notFull, &pCondLock->lock);
    }       

    //write the data to buffer
    Data[pCondLock->write_point] = data;
    pCondLock->write_point++;
    if(pCondLock->write_point == SIZE)
        pCondLock->write_point = 0;
    
    //unlock the mutex lock 
    pthread_mutex_unlock(&pCondLock->lock);

    //wake up the not_empty signal
    pthread_cond_signal(&pCondLock->notEmpty);
        

    return 0;
}


int get(int *data) 
{
    //obtain the mutex lock
    pthread_mutex_lock(&pCondLock->lock);
    
    //check the global variable Data empty or not
    while(pCondLock->write_point == pCondLock->read_point)
    {
        printf("The buf is empty, waitting for not_empty signal\n");
        pthread_cond_wait(&pCondLock->notEmpty, &pCondLock->lock);
    }       

    //read the data from buffer
    *data = Data[pCondLock->read_point];
    pCondLock->read_point++;
    if(pCondLock->read_point == SIZE)
        pCondLock->read_point = 0;
    
    //wake up the not_empty signal
    pthread_cond_signal(&pCondLock->notFull);
        
    pthread_mutex_unlock(&pCondLock->lock);

    return *data;
}

void *produce(void)
{
    int times=0;
    //1. first 5 times, every second write a data to buffer
    for(times=0; times < 5; times++)
    {
        sleep(1);
        put(times+1);
        printf("Input date=%d\n", times+1);
    }

    //2. last 5 times, every 3 seconds write a data to buffer 
    for(times = 5; times < 10; times++)
    {
        sleep(3);
        put(times+1);
        printf("Input date=%d\n", times+1);
    }
}

void *consume(void)
{
    int times=0;
    int data=0;
    //10 times, every 2 seconds read the buffer
    for(times = 0; times < 10; times++)
    {
        sleep(2);
        data = get(&data);
        printf("The data is %d\n", data);
    }
}

int main()
{
    pthread_t tid1, tid2;
    
    pCondLock = malloc(sizeof(sCOND));
    memset(pCondLock, '\0', sizeof(sCOND));
    //1.init the struct of sCondLock 
    init();

    //2. start two threads
    pthread_create(&tid1, NULL, (void*)*produce, NULL);
    pthread_create(&tid2, NULL, (void*)*consume, NULL);
    
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    free(pCondLock);

    return 0;
}

3). 读写锁:

四个线程:两读两写;

多进程可同时读,但此时不可写;
只有一个线程可写,其它线程等待该线程写完后执行响应的读/写操作

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

#define BUF_SIZE 128

char buf[BUF_SIZE];

pthread_rwlock_t rwlock;

int time_to_exit = 0;

void *read_first(void *arg);
void *read_second(void *arg);
void *write_first(void *arg);
void *write_second(void *arg);

int main()
{
    pthread_t tid_rd1, tid_rd2;
    pthread_t tid_wr1, tid_wr2;

    //1.create a read-write-lock
    int ret = pthread_rwlock_init(&rwlock, NULL);
    if(ret != 0)
    {
        perror("pthread_rwlock_init");
        exit(EXIT_FAILURE);
    }

    //2. Create the read and write threads
    ret = pthread_create(&tid_rd1, NULL, (void *)*read_first, NULL);
    if(ret != 0)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }

    ret = pthread_create(&tid_rd2, NULL, (void *)*read_second, NULL);
    if(ret != 0)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }

    ret = pthread_create(&tid_wr1, NULL, (void *)*write_first, NULL);
    if(ret != 0)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }

    ret = pthread_create(&tid_wr2, NULL, (void *)*write_second, NULL);
    if(ret != 0)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }


    //3. wait for the threads finish
    pthread_join(tid_rd1, NULL);
    pthread_join(tid_rd2, NULL);
    pthread_join(tid_wr1, NULL);
    pthread_join(tid_wr2, NULL);

    //4. delete the read-write-lock
    pthread_rwlock_destroy(&rwlock);

    return 0;
}

/***************************************************/
// Write threads
void *write_first(void *arg)
{
    while(!time_to_exit)
    {
        sleep(5);
        
        //1. get the read-lock    
        pthread_rwlock_wrlock(&rwlock);
        printf("\nThis is thread write_first!\n");

        printf("Pls input the string: ");
        fgets(buf, BUF_SIZE, stdin);

        pthread_rwlock_unlock(&rwlock);
    }

    printf("Exit the write_first!\n");
    pthread_exit(0);
}

void *write_second(void *arg)
{
    while(!time_to_exit)
    {
        sleep(10);
        
        //1. get the read-lock    
        pthread_rwlock_wrlock(&rwlock);
        printf("\nThis is thread write_second!\n");

        printf("Pls input the string: ");
        fgets(buf, BUF_SIZE, stdin);

        pthread_rwlock_unlock(&rwlock);
    }

    printf("Exit the write_second!\n");
    pthread_exit(0);
}


//-----2. read the threads
void *read_first(void *arg)
{
    while(1)
    {
        sleep(5);
        pthread_rwlock_rdlock(&rwlock);
        printf("\nThis is thread read_first\n");

        //if write an string of "end"
        if(!strncmp("end", buf, 3))
        {
            printf("Exit the read_first!\n");
            break;
        }
        
        //if nothing in the BUFFER
        while(strlen(buf) == 0)
        {
            pthread_rwlock_unlock(&rwlock);
            sleep(2);
            pthread_rwlock_rdlock(&rwlock);
        }
        
        //output the string in BUFFER
        printf("The string is: %s\n", buf);

        pthread_rwlock_unlock(&rwlock);
    }

    pthread_rwlock_unlock(&rwlock);

    //make the exit true
    time_to_exit = 1;

    pthread_exit(0);
}

void *read_second(void *arg)
{
    while(1)
    {
        sleep(4);

        pthread_rwlock_rdlock(&rwlock);
        printf("\nThis is thread read_second\n");

        //if write an string of "end"
        if(!strncmp("end", buf, 3))
        {
            printf("Exit the read_second!\n");
            break;
        }
        
        //if nothing in the BUFFER
        while(strlen(buf) == 0)
        {
            pthread_rwlock_unlock(&rwlock);
            sleep(2);
            pthread_rwlock_rdlock(&rwlock);
        }
        
        //output the string in BUFFER
        printf("The string is: %s\n", buf);

        pthread_rwlock_unlock(&rwlock);
    }

    pthread_rwlock_unlock(&rwlock);

    //make the exit true
    time_to_exit = 1;

    pthread_exit(0);
}

2. 异步机制 - 信号:

本程序包括两个线程:

  • 线程1安装SIGUSR1,阻塞除SIGUSR2外的所有信号;
  • 线程2安装SIGUSR2,不阻塞任何信号

操作流程:

  • 1- 线程1、2安装信号;
  • 2- 主线程发送SIGUSR1和SIGUSR2至线程1和线程2;
  • 3- 线程1接收到除SIGUSR2之外的信号,阻塞不执行;当收到SIGUSR2后,执行对应操作;
  • 4- 线程2接收到SIGUSR1和SIGUSR2后,分别执行对应操作
  • 5- 主线程发送SIGKILL信号,结束整个进程
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>

void *th_first(void *arg);

void *th_second(void *arg);

pthread_t tid1, tid2;

void handler(int signo)
{
    printf("In handler: tid_%s, signo=%d\n", ((pthread_self() == tid1)?"first":"second"), signo);
}

int main()
{
    int ret = 0;
    //1. create first thread
    ret = pthread_create(&tid1, NULL, (void *)*th_first, NULL);
    if(0 !=ret)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }
    //2. create second thread
    ret = pthread_create(&tid2, NULL, (void *)*th_second, NULL);
    if(0 !=ret)
    {
        perror("pthread_create");
        exit(EXIT_FAILURE);
    }

    sleep(2);
    //3. send the signal of SIG_USER1 and SIG_USER2 to thread_first
    ret = pthread_kill(tid1, SIGUSR1);
    if(0 !=ret)
    {
        perror("pthread_kill");
        exit(EXIT_FAILURE);
    }

    ret = pthread_kill(tid1, SIGUSR2);
    if(0 !=ret)
    {
        perror("pthread_kill");
        exit(EXIT_FAILURE);
    }

    //4. send the signal of SIG_USER1 and SIG_USER2 to thread_second_
    sleep(1);
    ret = pthread_kill(tid2, SIGUSR1);
    if(0 !=ret)
    {
        perror("pthread_kill");
        exit(EXIT_FAILURE);
    }

    ret = pthread_kill(tid2, SIGUSR2);
    if(0 !=ret)
    {
        perror("pthread_kill");
        exit(EXIT_FAILURE);
    }

    sleep(1);
    //5. send SIGKILL to all threads
    ret = pthread_kill(tid1, SIGKILL);
    if(0 !=ret)
    {
        perror("pthread_kill");
        exit(EXIT_FAILURE);
    }

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    return 0;
}


void *th_first(void *arg)
{
    //1. Add SIGUSR1 signal
    signal(SIGUSR1, handler);
    
    //2. Set the sinagl set
    sigset_t set;
    sigfillset(&set);                           //init set to be full, include all signal
    sigdelset(&set, SIGUSR2);                   //delete the SIGUSR2 from the set variable
    pthread_sigmask(SIG_SETMASK, &set, NULL);   //set the current mask set to be defined set variable
    
    //3. Circular wait the signal
    int i;
    for(i=0; i<5; i++)
    {
        printf("\nThis is th_first, tid=%#x\n ", pthread_self());
        pause();
    }
}

void *th_second(void *arg)
{
    usleep(100);
    //1. Add the signal of SIGUSR2
    signal(SIGUSR2, handler);

    //2. Circular wait the signal
    int i;
    for(i=0; i<5; i++)
    {
        printf("\nThis is th_second, tid=%#x\n", pthread_self());
        pause();
    }
}
posted @ 2017-11-12 19:01  Jimmy_Nie  阅读(...)  评论(...编辑  收藏