Linux多线程及线程同步简单实例

一、多线程基本概念

1. 线程的基本概念

① 线程就是轻量级的进程

②线程和创建他的进程共享代码段、数据段

③线程拥有自己的栈

2. 在实际应用中，多个线程往往会访问同一数据或资源，为避免线程之间相互影响，需要引入互斥机制，而互斥锁（mutex）是互斥机制中的一种

3. 简单实例

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

pthread_t work1Id;
pthread_t work2Id;

int work1Ret = 1;
int work2Ret = 2;

pthread_mutex_t mutex;

int number = 0;

void* Work1(void* args)
{
    int i = 0;
    
    printf("I am work%d
", *((int*)args));
    
    for(i = 0; i < 10; i++)
    {
        pthread_mutex_lock(&mutex);
        number++;
        pthread_mutex_unlock(&mutex);
        
        printf("I am work%d, number = %d
", *((int*)args), number);
        
        sleep(1);
    }
    
    return &work1Ret;
}

void* Work2(void* args)
{
    int i = 0;
    
    printf("I am work%d
", *((int*)args));
    
    for(i = 0; i < 10; i++)
    {
        pthread_mutex_lock(&mutex);
        number++;
        pthread_mutex_unlock(&mutex);
        
        printf("I am work%d, number = %d
", *((int*)args), number);
        
        sleep(1);
    }
    
    return &work2Ret;
}

int main()
{
    int args1 = 1;
    int args2 = 2;
    
    void* work1Ret = NULL;
    void* work2Ret = NULL; 
    
    pthread_mutex_init(&mutex, NULL);
    
    pthread_create(&work1Id, NULL, Work1, &args1);
    
    pthread_create(&work2Id, NULL, Work2, &args2);
    
    pthread_join(work1Id, &work1Ret);
    
    if(work1Ret != NULL)
    {
        printf("work1Ret = %d
", *((int*)work1Ret));
    }
    
    pthread_join(work2Id, &work2Ret);
    
    if(work2Ret != NULL)
    {
        printf("work2Ret = %d
", *((int*)work2Ret));
    }
    
    return 0;
}

二、线程同步

1. 多个线程按照规定的顺序来执行，即为线程同步。

2. 条件变量

①初始化

pthread_cond_t cond_ready = PTHREAD_COND_INITIALIZER;

②等待条件成熟

pthread_wait(&cond_ready, &mutex); //会对mutex先进行解锁操作

③设置成熟条件

pthread_cond_signal(&cond_ready)

3. 简单实例

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

pthread_t work1Id;
pthread_t work2Id;

int work1Ret = 1;
int work2Ret = 2;

pthread_cond_t cond_ready = PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

int number = 0;

void* Work1(void* args)
{
    int i = 0;
    
    printf("I am work%d
", *((int*)args));
    
    for(i = 0; i < 10; i++)
    {
        pthread_mutex_lock(&mutex);
        number++;
        
        if(number >= 10)
        {
            printf("I am work%d, Finish
", *((int*)args));
            pthread_cond_signal(&cond_ready);
        }
        
        pthread_mutex_unlock(&mutex);
        
        printf("I am work%d, number = %d
", *((int*)args), number);
        
        sleep(1);
    }
    
    return &work1Ret;
}

void* Work2(void* args)
{
    
    printf("I am work%d
", *((int*)args));
    pthread_mutex_lock(&mutex);
    
    if(number <= 10)
    {
        pthread_cond_wait(&cond_ready, &mutex);
        
        printf("I am work%d, number = %d
", *((int*)args), number);
    }
    
    return &work2Ret;
}

int main()
{
    int args1 = 1;
    int args2 = 2;
    
    void* work1Ret = NULL;
    void* work2Ret = NULL; 
    
    pthread_create(&work1Id, NULL, Work1, &args1);
    
    pthread_create(&work2Id, NULL, Work2, &args2);
    
    pthread_join(work1Id, &work1Ret);
    
    if(work1Ret != NULL)
    {
        printf("work1Ret = %d
", *((int*)work1Ret));
    }
    
    pthread_join(work2Id, &work2Ret);
    
    if(work2Ret != NULL)
    {
        printf("work2Ret = %d
", *((int*)work2Ret));
    }
    
    return 0;
}