Redis源码学习 --主从复制

前几天读了redis双链表的实现，一个标准的双链表，但是也实现了存储任意类型，用void*,真的是奇淫技巧，可能是我见识少，感觉也能实现内核链表那种感觉，今天看来记录一下。

首先是结构定义
```c
/* Node, List, and Iterator are the only data structures used currently. */

typedef struct listNode { //指针和数据耦合在一起，非侵入式
    struct listNode *prev;
    struct listNode *next;
    void *value;
} listNode;



typedef struct listIter {
    listNode *next;
    int direction; //迭代方向
} listIter;

typedef struct list {
    listNode *head;
    listNode *tail;
    void *(*dup)(void *ptr);  
    void (*free)(void *ptr);  //删除释放整个链表
    int (*match)(void *ptr, void *key);  匹配节点
    unsigned long len;
} list;


```

然后是一些简单的操作函数,用宏来实现
```c
/* Functions implemented as macros */
#define listLength(l) ((l)->len)
#define listFirst(l) ((l)->head)
#define listLast(l) ((l)->tail)
#define listPrevNode(n) ((n)->prev)
#define listNextNode(n) ((n)->next)
#define listNodeValue(n) ((n)->value)

#define listSetDupMethod(l,m) ((l)->dup = (m))
#define listSetFreeMethod(l,m) ((l)->free = (m))
#define listSetMatchMethod(l,m) ((l)->match = (m))

#define listGetDupMethod(l) ((l)->dup)
#define listGetFreeMethod(l) ((l)->free)
#define listGetMatchMethod(l) ((l)->match)
```
## 创建list并初始化
```c
list *listCreate(void)
{
    struct list *list;

    if ((list = zmalloc(sizeof(*list))) == NULL)
        return NULL;
    list->head = list->tail = NULL;
    list->len = 0;
    list->dup = NULL;
    list->free = NULL;
    list->match = NULL;
    return list;
}
```
## 删所有的节点
删除所有节点，初始化长度为0
```c
/* Remove all the elements from the list without destroying the list itself. */
void listEmpty(list *list)
{
    unsigned long len;
    listNode *current, *next;

    current = list->head;
    len = list->len;
    while(len--) {
        next = current->next;
        if (list->free) list->free(current->value);
        zfree(current);
        current = next;
    }
    list->head = list->tail = NULL;
    list->len = 0;
}

```
## 释放整个链表
```c
/* Free the whole list.
 *
 * This function can't fail. */
void listRelease(list *list)
{
    listEmpty(list);
    zfree(list);
}
```

## 头插法插入
```c
/* Add a new node to the list, to head, containing the specified 'value'
 * pointer as value.
 *
 * On error, NULL is returned and no operation is performed (i.e. the
 * list remains unaltered).
 * On success the 'list' pointer you pass to the function is returned. */
list *listAddNodeHead(list *list, void *value)
{
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    listLinkNodeHead(list, node);
    return list;
}

/*
 * Add a node that has already been allocated to the head of list
 */
void listLinkNodeHead(list* list, listNode *node) {
    if (list->len == 0) {
        list->head = list->tail = node;
        node->prev = node->next = NULL;
    } else {
        node->prev = NULL;
        node->next = list->head;
        list->head->prev = node;
        list->head = node;
    }
    list->len++;
}

```

## 尾插法插入
```c
/* Add a new node to the list, to tail, containing the specified 'value'
 * pointer as value.
 *
 * On error, NULL is returned and no operation is performed (i.e. the
 * list remains unaltered).
 * On success the 'list' pointer you pass to the function is returned. */
list *listAddNodeTail(list *list, void *value)
{
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    listLinkNodeTail(list, node);
    return list;
}

/*
 * Add a node that has already been allocated to the tail of list
 */
void listLinkNodeTail(list *list, listNode *node) {
    if (list->len == 0) {
        list->head = list->tail = node;
        node->prev = node->next = NULL;
    } else {
        node->prev = list->tail;
        node->next = NULL;
        list->tail->next = node;
        list->tail = node;
    }
    list->len++;
}

```
## 往中间插入节点
```c

list *listInsertNode(list *list, listNode *old_node, void *value, int after) {
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    if (after) {
        node->prev = old_node;
        node->next = old_node->next;
        if (list->tail == old_node) {
            list->tail = node;
        }
    } else {
        node->next = old_node;
        node->prev = old_node->prev;
        if (list->head == old_node) {
            list->head = node;
        }
    }
    if (node->prev != NULL) {
        node->prev->next = node;
    }
    if (node->next != NULL) {
        node->next->prev = node;
    }
    list->len++;
    return list;
}
```
## 删除节点
```
/* Remove the specified node from the specified list.
 * The node is freed. If free callback is provided the value is freed as well.
 *
 * This function can't fail. */
void listDelNode(list *list, listNode *node)
{
    listUnlinkNode(list, node);
    if (list->free) list->free(node->value);
    zfree(node);
}

/*
 * Remove the specified node from the list without freeing it.
 */
void listUnlinkNode(list *list, listNode *node) {
    if (node->prev)
        node->prev->next = node->next;
    else
        list->head = node->next;
    if (node->next)
        node->next->prev = node->prev;
    else
        list->tail = node->prev;

    node->next = NULL;
    node->prev = NULL;

    list->len--;
}

```
## 迭代器相关
```c
/* Returns a list iterator 'iter'. After the initialization every
 * call to listNext() will return the next element of the list.
 *
 * This function can't fail. */
listIter *listGetIterator(list *list, int direction)
{
    listIter *iter;

    if ((iter = zmalloc(sizeof(*iter))) == NULL) return NULL;
    if (direction == AL_START_HEAD)
        iter->next = list->head;
    else
        iter->next = list->tail;
    iter->direction = direction;
    return iter;
}

/* Release the iterator memory */
void listReleaseIterator(listIter *iter) {
    zfree(iter);
}


/* Create an iterator in the list private iterator structure */
void listRewind(list *list, listIter *li) {
    li->next = list->head;
    li->direction = AL_START_HEAD;
}

void listRewindTail(list *list, listIter *li) {
    li->next = list->tail;
    li->direction = AL_START_TAIL;
}

/* Return the next element of an iterator.
 * It's valid to remove the currently returned element using
 * listDelNode(), but not to remove other elements.
 *
 * The function returns a pointer to the next element of the list,
 * or NULL if there are no more elements, so the classical usage
 * pattern is:
 *
 * iter = listGetIterator(list,<direction>);
 * while ((node = listNext(iter)) != NULL) {
 *     doSomethingWith(listNodeValue(node));
 * }
 *
 * */
listNode *listNext(listIter *iter)
{
    listNode *current = iter->next;

    if (current != NULL) {
        if (iter->direction == AL_START_HEAD)
            iter->next = current->next;
        else
            iter->next = current->prev;
    }
    return current;
}

```

## 复制链表
```c
/* Duplicate the whole list. On out of memory NULL is returned.
 * On success a copy of the original list is returned.
 *
 * The 'Dup' method set with listSetDupMethod() function is used
 * to copy the node value. Otherwise the same pointer value of
 * the original node is used as value of the copied node.
 *
 * The original list both on success or error is never modified. */
list *listDup(list *orig)
{
    list *copy;
    listIter iter;
    listNode *node;

    if ((copy = listCreate()) == NULL)
        return NULL;
    copy->dup = orig->dup;
    copy->free = orig->free;
    copy->match = orig->match;
    listRewind(orig, &iter);
    while((node = listNext(&iter)) != NULL) {
        void *value;

        if (copy->dup) {
            value = copy->dup(node->value);
            if (value == NULL) {
                listRelease(copy);
                return NULL;
            }
        } else {
            value = node->value;
        }
        
        if (listAddNodeTail(copy, value) == NULL) {
            /* Free value if dup succeed but listAddNodeTail failed. */
            if (copy->free) copy->free(value);

            listRelease(copy);
            return NULL;
        }
    }
    return copy;
}

```

## 搜索值
```c
/* Search the list for a node matching a given key.
 * The match is performed using the 'match' method
 * set with listSetMatchMethod(). If no 'match' method
 * is set, the 'value' pointer of every node is directly
 * compared with the 'key' pointer.
 *
 * On success the first matching node pointer is returned
 * (search starts from head). If no matching node exists
 * NULL is returned. */
listNode *listSearchKey(list *list, void *key)
{
    listIter iter;
    listNode *node;

    listRewind(list, &iter);
    while((node = listNext(&iter)) != NULL) {
        if (list->match) {
            if (list->match(node->value, key)) {
                return node;
            }
        } else {
            if (key == node->value) {
                return node;
            }
        }
    }
    return NULL;
}
```
## 把一个链表加入另一个链表
被加入的链表清空
```c
/* Add all the elements of the list 'o' at the end of the
 * list 'l'. The list 'other' remains empty but otherwise valid. */
void listJoin(list *l, list *o) {
    if (o->len == 0) return;

    o->head->prev = l->tail;

    if (l->tail)
        l->tail->next = o->head;
    else
        l->head = o->head;

    l->tail = o->tail;
    l->len += o->len;

    /* Setup other as an empty list. */
    o->head = o->tail = NULL;
    o->len = 0;
}

/* Initializes the node's value and sets its pointers
 * so that it is initially not a member of any list.
 */
void listInitNode(listNode *node, void *value) {
    node->prev = NULL;
    node->next = NULL;
    node->value = value;
}

```
## 链接头尾
```c
/* Rotate the list removing the tail node and inserting it to the head. */
void listRotateTailToHead(list *list) {
    if (listLength(list) <= 1) return;

    /* Detach current tail */
    listNode *tail = list->tail;
    list->tail = tail->prev;
    list->tail->next = NULL;
    /* Move it as head */
    list->head->prev = tail;
    tail->prev = NULL;
    tail->next = list->head;
    list->head = tail;
}

/* Rotate the list removing the head node and inserting it to the tail. */
void listRotateHeadToTail(list *list) {
    if (listLength(list) <= 1) return;

    listNode *head = list->head;
    /* Detach current head */
    list->head = head->next;
    list->head->prev = NULL;
    /* Move it as tail */
    list->tail->next = head;
    head->next = NULL;
    head->prev = list->tail;
    list->tail = head;
}

```
差不多，就是一个很正常的双向链表，但是也很多奇淫技巧。

Redis双链表实现

上了大学之后就好久没碰日语了，最近打算重拾日语，毕竟学好了以后也是一门吃饭的活，码农码农，谁知道自己能干多久呢？多一门手艺多一门出路。

从今天开始（2023.11.16）,重新学习日语，但是也不打算系统性地学习，毕竟太累人了，每天看你一两篇日语新闻，听一两篇罢，单词能记多少记多少。

现阶段最重要的还是英语，时常很羡慕人家英语口语好的，奈何自己开不了口。看美剧罢，日积跬步，何以至千里。

其他也是一样的道理。

重拾日语

**What is Redis?**

**Redis is a fast in-memory NoSQL database and cache. Besides open-source, written in C, and designed for speed, Redis means “Remote Dictionary Server”.**

**Its fundamental data types are strings, lists, hashes, sets, and sorted sets; therefore Redis is often referred to as a data structure server. Many other data structures and capabilities for geolocation and stream processing are also available.**



**Redis’ various data structures are similar to the native data structures which are easily shared between processes and services, it’s great for rapid development and speedy applications.**

**Redis saves data in memory by default, with periodic disk persistence as an option. There are two kinds of disk persistence in Redis; RDB(Redis Database) and AOF(Append Only File). At certain intervals, RDB creates point-in-time snapshots of your dataset. AOF logs every write action received by the server, reconstructing the original dataset.**

**To prevent Redis from being full, you may set up a TTL(Time to live) to eject data when the specified amount of time elapsed.**

**This article focuses on Standalone Redis, Redis Sentinel for high availability, and Redis Cluster for automatic partitioning, as well as their advantages and disadvantages.**

**What is a Single Redis Instance?**

**It’s a solution using the single Redis node deployment architecture.**

---
## more

https://medium.com/@chaewonkong/redis-sentinel-vs-redis-cluster-a-comparative-overview-8c2561d3168f

https://medium.com/hepsiburadatech/redis-solutions-standalone-vs-sentinel-vs-cluster-f46e703307a9

What is Redis?

之前讲server启动的时候有个InitServerLast()函数
```c
/* Some steps in server initialization need to be done last (after modules
 * are loaded).
 * Specifically, creation of threads due to a race bug in ld.so, in which
 * Thread Local Storage initialization collides with dlopen call.
 * see: https://sourceware.org/bugzilla/show_bug.cgi?id=19329 */
void InitServerLast(void) {
    bioInit();   //初始化bio,其实是一个线程池
    initThreadedIO(); //也是一个专门用来处理IO的线程池
    set_jemalloc_bg_thread(server.jemalloc_bg_thread);
    server.initial_memory_usage = zmalloc_used_memory();
}
```
接下来讲解一下Bio,主要是bio.h,bio.c两个文件。

```c
#ifndef __BIO_H
#define __BIO_H

typedef void lazy_free_fn(void *args[]);

/* Exported API */
void bioInit(void);
unsigned long bioPendingJobsOfType(int type);
void bioDrainWorker(int job_type);
void bioKillThreads(void);
void bioCreateCloseJob(int fd, int need_fsync, int need_reclaim_cache);
void bioCreateCloseAofJob(int fd, long long offset, int need_reclaim_cache);
void bioCreateFsyncJob(int fd, long long offset, int need_reclaim_cache);
void bioCreateLazyFreeJob(lazy_free_fn free_fn, int arg_count, ...);

/* Background job opcodes */
enum {
    BIO_CLOSE_FILE = 0, /* Deferred close(2) syscall. */
    BIO_AOF_FSYNC,      /* Deferred AOF fsync. */
    BIO_LAZY_FREE,      /* Deferred objects freeing. */
    BIO_CLOSE_AOF,      /* Deferred close for AOF files. */
    BIO_NUM_OPS
};

#endif

```
## 初始化
主要是定了一些函数和任务类型
```c
/* Initialize the background system, spawning the thread. */
void bioInit(void) {
    pthread_attr_t attr;
    pthread_t thread;
    size_t stacksize;
    unsigned long j;

    /* Initialization of state vars and objects */
    for (j = 0; j < BIO_WORKER_NUM; j++) {
        pthread_mutex_init(&bio_mutex[j],NULL);
        pthread_cond_init(&bio_newjob_cond[j],NULL);
        bio_jobs[j] = listCreate();
    }

    /* 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 for. */
    for (j = 0; j < BIO_WORKER_NUM; j++) { //创建线程,默认三个
        void *arg = (void*)(unsigned long) j;
        if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
            serverLog(LL_WARNING, "Fatal: Can't initialize Background Jobs. Error message: %s", strerror(errno));
            exit(1);
        }
        bio_threads[j] = thread;
    }
}



//*******************************************************************************

static char* bio_worker_title[] = {
    "bio_close_file",
    "bio_aof",
    "bio_lazy_free",
};

#define BIO_WORKER_NUM (sizeof(bio_worker_title) / sizeof(*bio_worker_title))
```

## 任务结构体和相关数据结构
```c
 * file as the API does not expose the internals at all. */
typedef union bio_job {
    struct {
        int type; /* Job-type tag. This needs to appear as the first element in all union members. */
    } header;

    /* Job specific arguments.*/
    struct {
        int type;
        int fd; /* Fd for file based background jobs */
        long long offset; /* A job-specific offset, if applicable */
        unsigned need_fsync:1; /* A flag to indicate that a fsync is required before
                                * the file is closed. */
        unsigned need_reclaim_cache:1; /* A flag to indicate that reclaim cache is required before
                                * the file is closed. */
    } fd_args;

    struct {
        int type;
        lazy_free_fn *free_fn; /* Function that will free the provided arguments */
        void *free_args[]; /* List of arguments to be passed to the free function */
    } free_args;
} bio_job;


//**********************************************************************************
static unsigned int bio_job_to_worker[] = {
    [BIO_CLOSE_FILE] = 0,
    [BIO_AOF_FSYNC] = 1,
    [BIO_CLOSE_AOF] = 1,
    [BIO_LAZY_FREE] = 2,
};

static pthread_t bio_threads[BIO_WORKER_NUM];
static pthread_mutex_t bio_mutex[BIO_WORKER_NUM];
static pthread_cond_t bio_newjob_cond[BIO_WORKER_NUM];
static list *bio_jobs[BIO_WORKER_NUM];  //任务链表，默认三个双向链表
static unsigned long bio_jobs_counter[BIO_NUM_OPS] = {0};
```
## 线程栈大小(4M)
```c
/* Make sure we have enough stack to perform all the things we do in the
 * main thread. */
#define REDIS_THREAD_STACK_SIZE (1024*1024*4)
```

## 提交任务
```c
void bioSubmitJob(int type, bio_job *job) {
    job->header.type = type;
    unsigned long worker = bio_job_to_worker[type];
    pthread_mutex_lock(&bio_mutex[worker]);
    listAddNodeTail(bio_jobs[worker],job);
    bio_jobs_counter[type]++;
    pthread_cond_signal(&bio_newjob_cond[worker]);
    pthread_mutex_unlock(&bio_mutex[worker]);
}
```
## 创建任务（生产者）

```c
void bioCreateLazyFreeJob(lazy_free_fn free_fn, int arg_count, ...) {
    va_list valist;
    /* Allocate memory for the job structure and all required
     * arguments */
    bio_job *job = zmalloc(sizeof(*job) + sizeof(void *) * (arg_count));
    job->free_args.free_fn = free_fn;

    va_start(valist, arg_count);
    for (int i = 0; i < arg_count; i++) {
        job->free_args.free_args[i] = va_arg(valist, void *);
    }
    va_end(valist);
    bioSubmitJob(BIO_LAZY_FREE, job);
}

void bioCreateCloseJob(int fd, int need_fsync, int need_reclaim_cache) {
    bio_job *job = zmalloc(sizeof(*job));
    job->fd_args.fd = fd;
    job->fd_args.need_fsync = need_fsync;
    job->fd_args.need_reclaim_cache = need_reclaim_cache;

    bioSubmitJob(BIO_CLOSE_FILE, job);
}

void bioCreateCloseAofJob(int fd, long long offset, int need_reclaim_cache) {
    bio_job *job = zmalloc(sizeof(*job));
    job->fd_args.fd = fd;
    job->fd_args.offset = offset;
    job->fd_args.need_fsync = 1;
    job->fd_args.need_reclaim_cache = need_reclaim_cache;

    bioSubmitJob(BIO_CLOSE_AOF, job);
}

void bioCreateFsyncJob(int fd, long long offset, int need_reclaim_cache) {
    bio_job *job = zmalloc(sizeof(*job));
    job->fd_args.fd = fd;
    job->fd_args.offset = offset;
    job->fd_args.need_reclaim_cache = need_reclaim_cache;

    bioSubmitJob(BIO_AOF_FSYNC, job);
}

```
## 线程main函数（消费者）
就是一个循环，不断地取任务，区分任务类型
```c
void *bioProcessBackgroundJobs(void *arg) {
    bio_job *job;
    unsigned long worker = (unsigned long) arg;
    sigset_t sigset;

    /* Check that the worker is within the right interval. */
    serverAssert(worker < BIO_WORKER_NUM);

    redis_set_thread_title(bio_worker_title[worker]);

    redisSetCpuAffinity(server.bio_cpulist);

    makeThreadKillable();

    pthread_mutex_lock(&bio_mutex[worker]);
    /* 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))
        serverLog(LL_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[worker]) == 0) {
            pthread_cond_wait(&bio_newjob_cond[worker], &bio_mutex[worker]);
            continue;
        }
        /* Get the job from the queue. */
        ln = listFirst(bio_jobs[worker]);
        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[worker]);

        /* Process the job accordingly to its type. */
        int job_type = job->header.type;

        if (job_type == BIO_CLOSE_FILE) {
            if (job->fd_args.need_fsync &&
                redis_fsync(job->fd_args.fd) == -1 &&
                errno != EBADF && errno != EINVAL)
            {
                serverLog(LL_WARNING, "Fail to fsync the AOF file: %s",strerror(errno));
            }
            if (job->fd_args.need_reclaim_cache) {
                if (reclaimFilePageCache(job->fd_args.fd, 0, 0) == -1) {
                    serverLog(LL_NOTICE,"Unable to reclaim page cache: %s", strerror(errno));
                }
            }
            close(job->fd_args.fd);
        } else if (job_type == BIO_AOF_FSYNC || job_type == BIO_CLOSE_AOF) {
            /* The fd may be closed by main thread and reused for another
             * socket, pipe, or file. We just ignore these errno because
             * aof fsync did not really fail. */
            if (redis_fsync(job->fd_args.fd) == -1 &&
                errno != EBADF && errno != EINVAL)
            {
                int last_status;
                atomicGet(server.aof_bio_fsync_status,last_status);
                atomicSet(server.aof_bio_fsync_status,C_ERR);
                atomicSet(server.aof_bio_fsync_errno,errno);
                if (last_status == C_OK) {
                    serverLog(LL_WARNING,
                        "Fail to fsync the AOF file: %s",strerror(errno));
                }
            } else {
                atomicSet(server.aof_bio_fsync_status,C_OK);
                atomicSet(server.fsynced_reploff_pending, job->fd_args.offset);
            }

            if (job->fd_args.need_reclaim_cache) {
                if (reclaimFilePageCache(job->fd_args.fd, 0, 0) == -1) {
                    serverLog(LL_NOTICE,"Unable to reclaim page cache: %s", strerror(errno));
                }
            }
            if (job_type == BIO_CLOSE_AOF)
                close(job->fd_args.fd);
        } else if (job_type == BIO_LAZY_FREE) {
            job->free_args.free_fn(job->free_args.free_args);
        } else {
            serverPanic("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[worker]);
        listDelNode(bio_jobs[worker], ln);
        bio_jobs_counter[job_type]--;
        pthread_cond_signal(&bio_newjob_cond[worker]);
    }
}

```
## 其他函数
```c
/* Return the number of pending jobs of the specified type. */
unsigned long bioPendingJobsOfType(int type) {
    unsigned int worker = bio_job_to_worker[type];

    pthread_mutex_lock(&bio_mutex[worker]);
    unsigned long val = bio_jobs_counter[type];
    pthread_mutex_unlock(&bio_mutex[worker]);

    return val;
}

/* Wait for the job queue of the worker for jobs of specified type to become empty. */
void bioDrainWorker(int job_type) {
    unsigned long worker = bio_job_to_worker[job_type];

    pthread_mutex_lock(&bio_mutex[worker]);
    while (listLength(bio_jobs[worker]) > 0) {
        pthread_cond_wait(&bio_newjob_cond[worker], &bio_mutex[worker]);
    }
    pthread_mutex_unlock(&bio_mutex[worker]);
}

/* Kill the running bio threads in an unclean way. This function should be
 * used only when it's critical to stop the threads for some reason.
 * Currently Redis does this only on crash (for instance on SIGSEGV) in order
 * to perform a fast memory check without other threads messing with memory. */
void bioKillThreads(void) {
    int err;
    unsigned long j;

    for (j = 0; j < BIO_WORKER_NUM; j++) {
        if (bio_threads[j] == pthread_self()) continue;
        if (bio_threads[j] && pthread_cancel(bio_threads[j]) == 0) {
            if ((err = pthread_join(bio_threads[j],NULL)) != 0) {
                serverLog(LL_WARNING,
                    "Bio worker thread #%lu can not be joined: %s",
                        j, strerror(err));
            } else {
                serverLog(LL_WARNING,
                    "Bio worker thread #%lu terminated",j);
            }
        }
    }
}

```




复制方式

主从复制四大阶段

1.初始化阶段