关于redis的单线程与后台线程的源码分析

川长思鸟来 2022-07-13 06:14 96阅读 0赞

**前言：**

通常大家都会说**redis**是单线程的，这个理解其实也没错。

**redis**的命令处理基本上都是单线程处理的，除了个别任务会**fork**子进程进行处理。

分析版本：**redis 3.0.7**

**其实redis是个多线程进程，如下图：**

![SouthEast][]

**redis的另外两个线程的作用是什么？**

另外两个线程用于一些异步操作，通过条件变量控制任务，主要用于**close(2)，fsync(2)**的操作，

因为**close(2)**一个文件句柄时，如果程序是文件的最后一个拥有者，那么代表着要**unlink**它，相对来说会很慢，产生阻塞。

**源码在哪里？**

src/bio.h

src/bio.c

/* Initialize the background system, spawning the thread. */
    void bioInit(void) {
        pthread_attr_t attr;
        pthread_t thread;
        size_t stacksize;
        int j;
    
        /* Initialization of state vars and objects */
        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 */
        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. */
        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;
        }
    }

原文出自：[http://blog.csdn.net/daiyudong2020/article/details/53907415][http_blog.csdn.net_daiyudong2020_article_details_53907415]

End;

[SouthEast]: /images/20220713/69984208bde74645bc3d6ff10c84c5f6.png
[http_blog.csdn.net_daiyudong2020_article_details_53907415]: http://blog.csdn.net/daiyudong2020/article/details/53907415