Redis之quicklist源码分析

/* 
   quicklist结构占用32个字节（64位系统），其中字段：
   head：指向第一个quicklistnode。
   tail：指向最后一个quicklistnode。
   count：在所有ziplist中entry的个数总和。
   len：quicklistnode的个数。
   fill：ziplist大小限定，由server.list_max_ziplist_size给定。
   compress：节点压缩深度设置，由server.list-compress-depth给定，0表示关闭压缩。
 */
typedef struct quicklist {
    quicklistnode *head;
    quicklistnode *tail;
    unsigned long count;        /* total count of all entries in all ziplists */
    unsigned int len;           /* number of quicklistnodes */
    int fill : 16;              /* fill factor for individual nodes */
    unsigned int compress : 16; /* depth of end nodes not to compress;0=off */
} quicklist;

/*
 prev: 指向前一个quicklistnode。
 next: 指向下一个quicklistnode。
 zl: 指向当前节点的ziplist。
 sz：ziplist占用空间的字节数。
 count: ziplist中元素个数。
 encoding：编码类型，raw==1 or lzf==2。
 container：容器类型，none==1 or ziplist==2
 recompress：bool类型，true表示该节点数据临时被解压了。
 attempted_compress： bool类型，用于测试阶段。
 extra： 填充字典，将来可能会用到。
 */
typedef struct quicklistnode {
    struct quicklistnode *prev;
    struct quicklistnode *next;
    unsigned char *zl;
    unsigned int sz;             /* ziplist size in bytes */
    unsigned int count : 16;     /* count of items in ziplist */
    unsigned int encoding : 2;   /* raw==1 or lzf==2 */
    unsigned int container : 2;  /* none==1 or ziplist==2 */
    unsigned int recompress : 1; /* was this node previous compressed? */
    unsigned int attempted_compress : 1; /* node can't compress; too small */
    unsigned int extra : 10; /* more bits to steal for future usage */
} quicklistnode;

void pushgenericcommand(client *c, int where) {
    int j, waiting = 0, pushed = 0;
    robj *lobj = lookupkeywrite(c->db,c->argv[1]);

    if (lobj && lobj->type != obj_list) {
        addreply(c,shared.wrongtypeerr);
        return;
    }

    for (j = 2; j < c->argc; j++) {
        c->argv[j] = tryobjectencoding(c->argv[j]);
        if (!lobj) {  // key不存在，则首先创建key对象并加入db中
            lobj = createquicklistobject(); // 初始化quicklist对象
            quicklistsetoptions(lobj->ptr, server.list_max_ziplist_size,
                                server.list_compress_depth); // 使用redis server的配置项做初始化
            dbadd(c->db,c->argv[1],lobj); // 把quicklist添加到redis db中
        }
        // 把新元素加入list中
        listtypepush(lobj,c->argv[j],where);
        pushed++;
    }
    addreplylonglong(c, waiting + (lobj ? listtypelength(lobj) : 0));
    if (pushed) {
        char *event = (where == list_head) ? "lpush" : "rpush";

        signalmodifiedkey(c->db,c->argv[1]);
        notifykeyspaceevent(notify_list,event,c->argv[1],c->db->id);
    }
    server.dirty += pushed;
}

/* create a new quicklist.
 * free with quicklistrelease(). */
quicklist *quicklistcreate(void) {
    struct quicklist *quicklist;

    quicklist = zmalloc(sizeof(*quicklist));
    quicklist->head = quicklist->tail = null;
    quicklist->len = 0;
    quicklist->count = 0;
    quicklist->compress = 0;
    quicklist->fill = -2;
    return quicklist;
}

void listtypepush(robj *subject, robj *value, int where) {
    if (subject->encoding == obj_encoding_quicklist) {
        int pos = (where == list_head) ? quicklist_head : quicklist_tail;
        value = getdecodedobject(value);
        size_t len = sdslen(value->ptr);// 计算新元素长度
        quicklistpush(subject->ptr, value->ptr, len, pos); // 加入到quicklist
        decrrefcount(value); 
    } else {
        serverpanic("unknown list encoding");
    }
}

/* wrapper to allow argument-based switching between head/tail pop */
void quicklistpush(quicklist *quicklist, void *value, const size_t sz,
                   int where) {
    if (where == quicklist_head) {  // 添加到list头部
        quicklistpushhead(quicklist, value, sz);
    } else if (where == quicklist_tail) {  // 添加到list尾部
        quicklistpushtail(quicklist, value, sz);
    }
}

/* add new entry to head node of quicklist.
 *
 * returns 0 if used existing head.
 * returns 1 if new head created. 
 在quicklist的头部节点添加新元素：
 如果新元素添加在head中，返回0，否则返回1.
 */
int quicklistpushhead(quicklist *quicklist, void *value, size_t sz) {
    quicklistnode *orig_head = quicklist->head;
    // 如果head不为空，且空间大小满足新元素的存储要求，则新元素添加到head中，否则新加一个quicklistnode
    if (likely(
            _quicklistnodeallowinsert(quicklist->head, quicklist->fill, sz))) {
        quicklist->head->zl =
            ziplistpush(quicklist->head->zl, value, sz, ziplist_head);
        quicklistnodeupdatesz(quicklist->head);
    } else {
        // 创建新的quicklistnode
        quicklistnode *node = quicklistcreatenode();
        // 把新元素添加到新建的ziplist中
        node->zl = ziplistpush(ziplistnew(), value, sz, ziplist_head);
        // 更新ziplist的长度到quicklistnode的sz字段，再把新node添加到quicklist中，即添加到原head前面
        quicklistnodeupdatesz(node);
        _quicklistinsertnodebefore(quicklist, quicklist->head, node);
    }
    quicklist->count++;
    quicklist->head->count++;
    return (orig_head != quicklist->head);
}

/* default pop function
 *
 * returns malloc'd value from quicklist */
int quicklistpop(quicklist *quicklist, int where, unsigned char **data,
                 unsigned int *sz, long long *slong) {
    unsigned char *vstr;
    unsigned int vlen;
    long long vlong;
    if (quicklist->count == 0)
        return 0;
    // pop一个元素
    int ret = quicklistpopcustom(quicklist, where, &vstr, &vlen, &vlong,
                                 _quicklistsaver);
    if (data)
        *data = vstr;
    if (slong)
        *slong = vlong;
    if (sz)
        *sz = vlen;
    return ret;
}

/* pop from quicklist and return result in 'data' ptr.  value of 'data'
 * is the return value of 'saver' function pointer if the data is not a number.
 *
 * if the quicklist element is a long long, then the return value is returned in
 * 'sval'.
 *
 * return value of 0 means no elements available.
 * return value of 1 means check 'data' and 'sval' for values.
 * if 'data' is set, use 'data' and 'sz'.  otherwise, use 'sval'. 
 如果quicklist中无元素，返回0，否则返回1.
 当返回1时，需要检查data和sval两个字段：
 1. 如果是string类型，则把结果地址保存在data指针中，长度保存在sz。
 2. 如果是long long类型，则把值保存在sval字段中。
 */
int quicklistpopcustom(quicklist *quicklist, int where, unsigned char **data,
                       unsigned int *sz, long long *sval,
                       void *(*saver)(unsigned char *data, unsigned int sz)) {
    unsigned char *p;
    unsigned char *vstr;
    unsigned int vlen;
    long long vlong;
    int pos = (where == quicklist_head) ? 0 : -1;

    if (quicklist->count == 0)
        return 0;

    if (data)
        *data = null;
    if (sz)
        *sz = 0;
    if (sval)
        *sval = -123456789;

    quicklistnode *node;
    if (where == quicklist_head && quicklist->head) {
        node = quicklist->head;
    } else if (where == quicklist_tail && quicklist->tail) {
        node = quicklist->tail;
    } else {
        return 0;
    }
    // p: 0 取ziplist的第一个元素； -1 取ziplist的最后一个元素；
    p = ziplistindex(node->zl, pos);
    if (ziplistget(p, &vstr, &vlen, &vlong)) {
        if (vstr) {
            if (data)
                *data = saver(vstr, vlen);
            if (sz)
                *sz = vlen;
        } else {
            if (data)
                *data = null;
            if (sval)
                *sval = vlong;
        }
        // 从quicklist中删除该元素
        quicklistdelindex(quicklist, node, &p);
        return 1;
    }
    return 0;
}

/* delete one entry from list given the node for the entry and a pointer
 * to the entry in the node.
 *
 * note: quicklistdelindex() *requires* uncompressed nodes because you
 *       already had to get *p from an uncompressed node somewhere.
 *
 * returns 1 if the entire node was deleted, 0 if node still exists.
 * also updates in/out param 'p' with the next offset in the ziplist. 
 从quicklistnode中删除一个entry：
 1. 从ziplist中删除entry。
 2. quicklistnode中的entry个数减1：
    如果quicklistnode中entry个数为0，则从quicklist中删除当前的quicklistnode。
    否则，更新quicklistnode中的sz字段。
 */
redis_static int quicklistdelindex(quicklist *quicklist, quicklistnode *node,
                                   unsigned char **p) {
    int gone = 0;

    node->zl = ziplistdelete(node->zl, p);
    node->count--;
    if (node->count == 0) {
        gone = 1;
        __quicklistdelnode(quicklist, node);
    } else {
        quicklistnodeupdatesz(node);
    }
    quicklist->count--;
    /* if we deleted the node, the original node is no longer valid */
    return gone ? 1 : 0;
}