Redis 数据持久化（一）

Redis的模块化开发设计的还是相当不错的，在Bio.h和Bio.c文件中定义了一个多线程的文件任务处理模块，在添加和处理任务的时候使用互斥锁和条件变量进行的同步，而且本身也支持多线程，这个模块的支持两个类型，一个是关闭文件，另一个是将内存中的数据刷新到磁盘中去，也算是数据持久化的一部分了。其中三个宏定义了这些数据。

#define REDIS_BIO_CLOSE_FILE    0 /*关闭一个系统调用*/
#define REDIS_BIO_AOF_FSYNC     1 /*文件数据刷新到磁盘*/
#define REDIS_BIO_NUM_OPS       2/*支持任务类型数*/

模块的基础变量数据：

static pthread_t bio_threads[REDIS_BIO_NUM_OPS];/*多线程情况下线程的个数*/
static pthread_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];/*互斥锁*/
static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];/*条件变量*/
static list *bio_jobs[REDIS_BIO_NUM_OPS];/*后台任务链表，每个线程一个，根据下标区分*/
static unsigned long long bio_pending[REDIS_BIO_NUM_OPS];/*记录每个线程剩余的任务数*/
struct bio_job 
{/*后台IO节点，任务是通过链表来维护的，这个算是链表内的节点数据，第一个是创建时间，第二个是指定参数。*/
    time_t time; /* Time at which the job was created. */
    /* Job specific arguments pointers. If we need to pass more than three
     * arguments we can just pass a pointer to a structure or alike. */
    void *arg1, *arg2, *arg3;
};

具体的实现接口，注意，这个模块中.h和.c文件中定义的接口不一样，不知道是写错了还是怎么回事，.h中定义的部分接口没有实现：

void bioInit(void); /初始化变量数据和线程数据/
void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3);/*添加一个任务*/void *bioProcessBackgroundJobs(void *arg);/*处理指定的任务数组*/
unsigned long long bioPendingJobsOfType(int type);/*获取剩余的任务数*/
void bioKillThreads(void);/*关闭线程*/

1.void bioInit(void);

void bioInit(void) 
{
    pthread_attr_t attr;
    pthread_t thread;
    size_t stacksize;
    int j;

    /*初始化条件变量和互斥锁*/
    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;
    }

    /*初始化线程属性，自动增加线程栈的大小*/
    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. */
    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;
    }
}//这个没啥可说的，无非是初始化同步的数据和线程数据

void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3);/*添加一个任务*/

/*创建一个后台任务，创建任务支持多线程
添加事件和处理事件就像是消费者和生产者的问题一样，采用互斥和条件变量来控制
参数1是添加到哪个队列中，剩余是三个参数*/
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;
    /*添加的时候要注意并发问题，添加完了发个信号*/
    pthread_mutex_lock(&bio_mutex[type]);
    listAddNodeTail(bio_jobs[type],job);
    bio_pending[type]++;
    pthread_cond_signal(&bio_condvar[type]);
    pthread_mutex_unlock(&bio_mutex[type]);
}

void *bioProcessBackgroundJobs(void *arg);

/*事件消费函数*/
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);/*设置线程为收到cancle信号马上退出*/
    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(SIG_BLOCK, &sigset, NULL))
        redisLog(REDIS_WARNING,
            "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));

    while(1) 
    {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) 
        {
            pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
            continue;
        }
        /* Pop the job from the queue. */
        ln = listFirst(bio_jobs[type]);
        job = ln->value;
        /* It is now possible to unlock the background system as we know have
         * a stand alone job structure to process.*/
        pthread_mutex_unlock(&bio_mutex[type]);
　　　　 /*处理任务的时候解除互斥锁，提高效率*/
        /* 区分任务类型，具体执行 */
        if (type == REDIS_BIO_CLOSE_FILE) 
        {
            close((long)job->arg1);
        } 
        else if (type == REDIS_BIO_AOF_FSYNC) 
        {
            aof_fsync((long)job->arg1);
        } 
        else 
        {
            redisPanic("Wrong job type in bioProcessBackgroundJobs().");
        }
        zfree(job);

        /* Lock again before reiterating the loop, if there are no longer
         * jobs to process we'll block again in pthread_cond_wait(). */
        pthread_mutex_lock(&bio_mutex[type]);/*修改公共资源的的是要加锁发，防止并发问题*/
        listDelNode(bio_jobs[type],ln);/*删除节点，并减掉任务数*/
        bio_pending[type]--;
    }
}

void bioKillThreads(void);/*关闭线程*/

void bioKillThreads(void) 
{
    int err, j;

    for (j = 0; j < REDIS_BIO_NUM_OPS; j++) 
    {
        if (pthread_cancel(bio_threads[j]) == 0) /*给线程发送结束信号，发送成功之后等待其结束*/
        {
            if ((err = pthread_join(bio_threads[j],NULL)) != 0) 
            {
                redisLog(REDIS_WARNING,"Bio thread for job type #%d can be joined: %s",j, strerror(err));
            }
            else 
            {
                redisLog(REDIS_WARNING,"Bio thread for job type #%d terminated",j);
            }
        }
    }
}

这个后台任务值负责关闭系统的调用和数据的持久化。