主要看下redis是怎么使用多线程的

先说明下redis也是多线程的.但是redis的主线程处理业务.而其他三个线程跟主要功能是关系不到的

redis的三个线程主要是做什么

初始化入口

void initServer(void) {     ...     bioInit();     ... }

初始化后redis其他后台线程.

void bioInit(void) {     pthread_attr_t attr;     pthread_t thread;     size_t stacksize;     int j;      /* Initialization of state vars and objects       *      * 初始化 job 队列，以及线程状态      */     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {         pthread_mutex_init(&bio_mutex[j],NULL);         pthread_cond_init(&bio_condvar[j],NULL);         bio_jobs[j] = listCreate();         bio_pending[j] = 0;     }      /* Set the stack size as by default it may be small in some system       *      * 设置栈大小      */     pthread_attr_init(&attr);     pthread_attr_getstacksize(&attr,&stacksize);     if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */     while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;     pthread_attr_setstacksize(&attr, stacksize);      /* Ready to spawn our threads. We use the single argument the thread      * function accepts in order to pass the job ID the thread is      * responsible of.       *      * 创建线程      */     for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {         void *arg = (void*)(unsigned long) j;         if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {             redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");             exit(1);         }         bio_threads[j] = thread;     } }

初始化三类线程. 这三类线程被认为是后台执行.不影响主线程

1. BIO_CLOSE_FILE . 关闭重写之前的aof文件.
2. BIO_AOF_FSYNC . 定时刷新数据到磁盘上.
3. BIO_LAZY_FREE . 惰性删除过期时间数据

redis为了保证其高效.一些比较耗时的动作会起线程或者进程来完成.不会阻塞在业务主线程上.

使用多线程的特点

• 创建3个线程.这个三个线程的功能互不影响
• 每个线程都有一个工作队列.主线程生产任务放到任务队里.这三个线程消费这些任务.
• 任务队列和取出消费的时候都得加锁.防止竞争
• 使用条件变量来等待任务.以及通知

// 存放工作的队列 static list *bio_jobs[REDIS_BIO_NUM_OPS];

bio_jobs是一个双端链表结构

void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) {     struct bio_job *job = zmalloc(sizeof(*job));      job->time = time(NULL);     job->arg1 = arg1;     job->arg2 = arg2;     job->arg3 = arg3;      pthread_mutex_lock(&bio_mutex[type]);      // 将新工作推入队列     listAddNodeTail(bio_jobs[type],job);     bio_pending[type]++;      pthread_cond_signal(&bio_condvar[type]);      pthread_mutex_unlock(&bio_mutex[type]); }

当有任务的时候.先把任务丢到redis工作队列里.这里记得加锁

void *bioProcessBackgroundJobs(void *arg) {     struct bio_job *job;     unsigned long type = (unsigned long) arg;     sigset_t sigset;      /* Make the thread killable at any time, so that bioKillThreads()      * can work reliably. */     pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);     pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);      pthread_mutex_lock(&bio_mutex[type]);     /* Block SIGALRM so we are sure that only the main thread will      * receive the watchdog signal. */     sigemptyset(&sigset);     sigaddset(&sigset, SIGALRM);     if (pthread_sigmask(<