Linux多線程及線程同步簡單實例

一、多線程基本概念

1. 線程的基本概念

① 線程就是輕量級的進程

②線程和創建他的進程共享代碼段、數據段

③線程擁有自己的棧

2. 在實際應用中，多個線程往往會訪問同一數據或資源，為避免線程之間相互影響，需要引入互斥機制，而互斥鎖（mutex）是互斥機制中的一種

3. 簡單實例

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

void* Work2(void* args)
{
    int i = 0;
    
    printf("I am work%d\n", *((int*)args));
    
    for(i = 0; i < 10; i++)
    {
        pthread_mutex_lock(&mutex);
        number++;
        pthread_mutex_unlock(&mutex);
        
        printf("I am work%d, number = %d\n", *((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\n", *((int*)work1Ret));
    }
    
    pthread_join(work2Id, &work2Ret);
    
    if(work2Ret != NULL)
    {
        printf("work2Ret = %d\n", *((int*)work2Ret));
    }
    
    return 0;
}

 

二、線程同步

1. 多個線程按照規定的順序來執行，即為線程同步。

2. 條件變量

①初始化

pthread_cond_t cond_ready = PTHREAD_COND_INITIALIZER;

②等待條件成熟

pthread_wait(&cond_ready, &mutex); //會對mutex先進行解鎖操作

③設置成熟條件

pthread_cond_signal(&cond_ready)

3. 簡單實例

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

void* Work2(void* args)
{
    
    printf("I am work%d\n", *((int*)args));
    pthread_mutex_lock(&mutex);
    
    if(number <= 10)
    {
        pthread_cond_wait(&cond_ready, &mutex);
        
        printf("I am work%d, number = %d\n", *((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\n", *((int*)work1Ret));
    }
    
    pthread_join(work2Id, &work2Ret);
    
    if(work2Ret != NULL)
    {
        printf("work2Ret = %d\n", *((int*)work2Ret));
    }
    
    return 0;
}