什么是線程

線程是在共享內(nèi)存空間種并發(fā)的多道執(zhí)行路徑，它們共享一個(gè)進(jìn)程的資源。進(jìn)程是系統(tǒng)中程序執(zhí)行和資源分配的基本單位。線程是進(jìn)程內(nèi)的基本調(diào)度單位，也可以稱為輕量級(jí)進(jìn)程

線程分類

1. 用戶級(jí)線程

2. 核心級(jí)線程

線程基本操作

由于線程共享進(jìn)程的資源和地址空間，因此在對(duì)這些資源進(jìn)行操作時(shí)，必須考慮到線程間資源訪問(wèn)的唯一性問(wèn)題，這里介紹的是POSIX中線程同步的方法，主要有互斥鎖和信號(hào)量的方式

互斥鎖

互斥鎖只有兩種狀態(tài)，就是上鎖和解鎖?；コ怄i使得共享資源按序在各個(gè)線程中操作?？煞譃?#xff1a;快速鎖、遞歸互斥鎖、檢錯(cuò)互斥鎖

信號(hào)量

信號(hào)量也是操作系統(tǒng)中所用到的PV原語(yǔ)，它廣泛用于進(jìn)程或線程間的同步與互斥，本質(zhì)上是非負(fù)的整數(shù)計(jì)數(shù)器，當(dāng)信號(hào)量sem的值大于或等于0時(shí)，該線程具有公共資源的訪問(wèn)權(quán)限?；コ馀c同步的區(qū)別在于，互斥用的是同一個(gè)信號(hào)量，同步反之。

Example

線程創(chuàng)建

#include #include #include void *pthread_2(void *param){    int i;    // pthread_cancel(*(pthread_t *)param);    // 取消th1線程，那么就不會(huì)去執(zhí)行pthread_1函數(shù)了    for (i = 0; i < 10; i++)    {         printf("我是線程2:%d/n", i);         sleep(1);         if(i == 5)         {            pthread_exit("exit");         }    }}void *pthread_1(void *param){    pthread_cancel(*(pthread_t *)param);    // 根據(jù)創(chuàng)建線程的函數(shù)，會(huì)先執(zhí)行pthread_2一次然后回到pthread_1函數(shù)    // 但是又把th2傳過(guò)來(lái)，把th2線程取消掉    while (1)    {        printf("我是線程1/n");        sleep(1);    }    }int main(int argc, char *argv[]){    pthread_t th1,th2;    printf("主進(jìn)程，下面開(kāi)始創(chuàng)建線程/n");    pthread_create(&th1, NULL, pthread_1, (void *)&th2);    // 創(chuàng)建線程標(biāo)識(shí)符為th1，pthread_1是線程起始地址    pthread_create(&th2, NULL, pthread_2, (void *)&th1);    // 創(chuàng)建線程標(biāo)識(shí)符為th2，pthread_2是線程起始地址，把th1傳到pthread_2中    printf("線程創(chuàng)建結(jié)束/n");    pthread_join(th1, NULL);    // 將線程掛起，等待結(jié)束    pthread_join(th2, NULL);}

互斥鎖

#include #include #include pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; // 互斥鎖// 創(chuàng)建快速互斥鎖int flag = 0;void *pthread_2(void *param){    int i;    pthread_mutex_lock(&mutex);    // 鎖住線程資源    for (i = 0; i < 10; i++)    {         printf("我是線程2:%d/n", i);         sleep(1);    }    pthread_mutex_unlock(&mutex);    // 解鎖}void *pthread_1(void *param){    int i;    pthread_mutex_lock(&mutex);    for (i = 0; i < 10; i++)    {         printf("我是線程1:%d/n", i);         sleep(1);    }    pthread_mutex_unlock(&mutex);}int main(int argc, char *argv[]){    pthread_t th1,th2;    //pthread_mutex_init(&mutex, PTHREAD_MUTEX_INITIALIZER);    printf("主進(jìn)程，下面開(kāi)始創(chuàng)建線程/n");    pthread_create(&th1, NULL, pthread_1, NULL);    pthread_create(&th2, NULL, pthread_2, (void *)&th1);    // 會(huì)先去執(zhí)行th1的線程    printf("線程創(chuàng)建結(jié)束/n");    pthread_join(th1, NULL);    // 將線程吊起    pthread_join(th2, NULL);}

信號(hào)量

信號(hào)量互斥

#include #include #include #include sem_t sem;//sem信號(hào)量實(shí)現(xiàn)三個(gè)線程互斥void *pthread_3(void *param){    int i;    sem_wait(&sem); //sem = sem -1;      for (i = 0; i < 10; i++)    {         printf("我是線程3:%d/n", i);         sleep(1);    }    sem_post(&sem);  //sem = sem + 1; }void *pthread_2(void *param){    int i;    sem_wait(&sem); //sem = sem -1;      for (i = 0; i < 10; i++)    {         printf("我是線程2:%d/n", i);         sleep(1);    }    sem_post(&sem);  //sem = sem + 1; }void *pthread_1(void *param){    int i;    sem_wait(&sem);  //sem = sem -1;      for (i = 0; i < 10; i++)    {         printf("我是線程1:%d/n", i);         sleep(1);    }    sem_post(&sem);  //sem = sem + 1; }int main(int argc, char *argv[]){    pthread_t th1,th2, th3;    sem_init(&sem, 0, 1);    // 信號(hào)量初始化1    printf("主進(jìn)程，下面開(kāi)始創(chuàng)建線程/n");    pthread_create(&th1, NULL, pthread_1, NULL);    pthread_create(&th2, NULL, pthread_2, NULL);    // 首先去執(zhí)行th1線程    pthread_create(&th3, NULL, pthread_3, NULL);    printf("線程創(chuàng)建結(jié)束/n");    pthread_join(th1, NULL);    // 將線程掉起    pthread_join(th2, NULL);    pthread_join(th3, NULL);}

信號(hào)量同步

#include #include #include #include sem_t sem1, sem2, sem3;//3個(gè)線程1，2，3//執(zhí)行順序 3 1 2void *pthread_3(void *param){    int i;    sem_wait(&sem1); //sem = sem -1;    for (i = 0; i < 10; i++)    {        printf("我是線程3:%d/n", i);        sleep(1);    }    sem_post(&sem3); //sem = sem + 1;}void *pthread_2(void *param){    int i;    sem_wait(&sem2); //sem = sem -1;    for (i = 0; i < 10; i++)    {        printf("我是線程2:%d/n", i);        sleep(1);    }    sem_post(&sem1); //sem = sem + 1;}void *pthread_1(void *param){    int i;    sem_wait(&sem3); //sem = sem -1;    for (i = 0; i < 10; i++)    {        printf("我是線程1:%d/n", i);        sleep(1);    }    sem_post(&sem2); //sem = sem + 1;}int main(int argc, char *argv[]){    pthread_t th1, th2, th3;    sem_init(&sem1, 0, 1);    sem_init(&sem2, 0, 0);    sem_init(&sem3, 0, 0);    printf("主進(jìn)程，下面開(kāi)始創(chuàng)建線程/n");    pthread_create(&th1, NULL, pthread_1, NULL);    pthread_create(&th2, NULL, pthread_2, NULL);    pthread_create(&th3, NULL, pthread_3, NULL);    // 初始化后，sem1 = 0 ,sem2 ,sem3 =-1    printf("線程創(chuàng)建結(jié)束/n");    pthread_join(th1, NULL);    pthread_join(th2, NULL);    pthread_join(th3, NULL);}

函數(shù)說(shuō)明

pthread_create

pthread_exit

pthread_join

pthread_mutex_init

pthread_mutex_lock

pthread_mutex_trylock

pthread_mutex_unlock

pthread_mutex_destroy

sem_init

sem_wait

sem_trywait

sem_post

sem_getvalue

sem_destroy