Redis（六）：list/lpush/lrange/lpop 命令源码解析
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上一篇讲了hash数据类型的相关实现方法，没有茅塞顿开也至少知道redis如何搞事情的了吧。
本篇咱们继续来看redis中的数据类型的实现: list 相关操作实现。
同样，我们以使用者的角度，开始理解list提供的功能，相应的数据结构承载，再到具体实现，以这样一个思路来理解redis之list。
零、redis list相关操作方法
从官方的手册中可以查到相关的使用方法。
1> BLPOP key1 [key2] timeout
功能: 移出并获取列表的第一个元素， 如果列表没有元素会阻塞列表直到等待超时或发现可弹出元素为止。（LPOP的阻塞版本）
返回值: 获取到元素的key和被弹出的元素值2> BRPOP key1 [key2 ] timeout
功能: 移出并获取列表的最后一个元素， 如果列表没有元素会阻塞列表直到等待超时或发现可弹出元素为止。（RPOP 的阻塞版本）
返回值: 获取到元素的key和被弹出的元素值3> BRPOPLPUSH source destination timeout
功能: 从列表中弹出一个值，将弹出的元素插入到另外一个列表中并返回它； 如果列表没有元素会阻塞列表直到等待超时或发现可弹出元素为止。（RPOPLPUSH 的阻塞版本）
返回值: 被转移的元素值或者为nil4> LINDEX key index
功能: 通过索引获取列表中的元素
返回值: 查找到的元素值,超出范围时返回nil5> LINSERT key BEFORE|AFTER pivot value
功能: 在列表的元素前或者后插入元素
返回值: 插入后的list长度6> LLEN key
功能: 获取列表长度
返回值: 列表长度7> LPOP key
功能: 移出并获取列表的第一个元素
返回值: 第一个元素或者nil8> LPUSH key value1 [value2]
功能: 将一个或多个值插入到列表头部
返回值: 插入后的list长度9> LPUSHX key value
将一个值插入到已存在的列表头部，如果key不存在则不做任何操作
返回值: 插入后的list长度10> LRANGE key start stop
功能: 获取列表指定范围内的元素 （包含起止边界）
返回值: 值列表11> LREM key count value
功能: 移除列表元素, count>0:移除正向匹配的count个元素,count<0:移除逆向匹配的count个元素, count=0,只移除匹配的元素
返回值: 移除的元素个数12> LSET key index value
功能: 通过索引设置列表元素的值
返回值: OK or err13> LTRIM key start stop
功能: 对一个列表进行修剪(trim)，就是说，让列表只保留指定区间内的元素，不在指定区间之内的元素都将被删除。
返回值: OK14> RPOP key
功能: 移除列表的最后一个元素，返回值为移除的元素。
返回值: 最后一个元素值或者nil15> RPOPLPUSH source destination
功能: 移除列表的最后一个元素，并将该元素添加到另一个列表并返回
返回值: 被转移的元素16> RPUSH key value1 [value2]
功能: 在列表中添加一个或多个值
返回值: 插入后的list长度17> RPUSHX key value
功能: 为已存在的列表添加值
返回值: 插入后的list长度
redis中的实现方法定义如下:
{"rpush",rpushCommand,-3,"wmF",0,NULL,1,1,1,0,0},
{"lpush",lpushCommand,-3,"wmF",0,NULL,1,1,1,0,0},
{"rpushx",rpushxCommand,3,"wmF",0,NULL,1,1,1,0,0},
{"lpushx",lpushxCommand,3,"wmF",0,NULL,1,1,1,0,0},
{"linsert",linsertCommand,5,"wm",0,NULL,1,1,1,0,0},
{"rpop",rpopCommand,2,"wF",0,NULL,1,1,1,0,0},
{"lpop",lpopCommand,2,"wF",0,NULL,1,1,1,0,0},
{"brpop",brpopCommand,-3,"ws",0,NULL,1,1,1,0,0},
{"brpoplpush",brpoplpushCommand,4,"wms",0,NULL,1,2,1,0,0},
{"blpop",blpopCommand,-3,"ws",0,NULL,1,-2,1,0,0},
{"llen",llenCommand,2,"rF",0,NULL,1,1,1,0,0},
{"lindex",lindexCommand,3,"r",0,NULL,1,1,1,0,0},
{"lset",lsetCommand,4,"wm",0,NULL,1,1,1,0,0},
{"lrange",lrangeCommand,4,"r",0,NULL,1,1,1,0,0},
{"ltrim",ltrimCommand,4,"w",0,NULL,1,1,1,0,0},
{"lrem",lremCommand,4,"w",0,NULL,1,1,1,0,0},
{"rpoplpush",rpoplpushCommand,3,"wm",0,NULL,1,2,1,0,0},
一、list相关数据结构
说到list或者说链表，我们能想到什么数据结构呢？单向链表、双向链表、循环链表... 好像都挺简单的，还有啥？？ 我们来看下redis 的实现:
// quicklist 是其实数据容器，由head,tail 进行迭代，所以算是一个双向链表
/* quicklist is a 32 byte struct (on 64-bit systems) describing a quicklist.
* 'count' is the number of total entries.
* 'len' is the number of quicklist nodes.
* 'compress' is: -1 if compression disabled, otherwise it's the number
* of quicklistNodes to leave uncompressed at ends of quicklist.
* 'fill' is the user-requested (or default) fill factor. */
typedef struct quicklist {
// 头节点
quicklistNode *head;
// 尾节点
quicklistNode *tail;
// 现有元素个数
unsigned long count; /* total count of all entries in all ziplists */
// 现有的 quicklistNode 个数，一个 node 可能包含n个元素
unsigned int len; /* number of quicklistNodes */
// 填充因子
int fill : 16; /* fill factor for individual nodes */
// 多深的链表无需压缩
unsigned int compress : 16; /* depth of end nodes not to compress;0=off */
} quicklist;
// 链表中的每个节点
typedef struct quicklistEntry {
const quicklist *quicklist;
quicklistNode *node;
// 当前迭代元素的ziplist的偏移位置指针
unsigned char *zi;
// 纯粹的 value, 值来源 zi
unsigned char *value;
// 占用空间大小
unsigned int sz;
long long longval;
// 当前节点偏移
int offset;
} quicklistEntry;
// 链表元素节点使用 quicklistNode
/* quicklistNode is a 32 byte struct describing a ziplist for a quicklist.
* We use bit fields keep the quicklistNode at 32 bytes.
* count: 16 bits, max 65536 (max zl bytes is 65k, so max count actually < 32k).
* encoding: 2 bits, RAW=1, LZF=2.
* container: 2 bits, NONE=1, ZIPLIST=2.
* recompress: 1 bit, bool, true if node is temporarry decompressed for usage.
* attempted_compress: 1 bit, boolean, used for verifying during testing.
* extra: 12 bits, free for future use; pads out the remainder of 32 bits */
typedef struct quicklistNode {
struct quicklistNode *prev;
struct quicklistNode *next;
// zl 为ziplist链表，保存count个元素值
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;
// list迭代器
typedef struct quicklistIter {
const quicklist *quicklist;
quicklistNode *current;
unsigned char *zi;
long offset; /* offset in current ziplist */
int direction;
} quicklistIter;
// ziplist 数据结构
typedef struct zlentry {
unsigned int prevrawlensize, prevrawlen;
unsigned int lensize, len;
unsigned int headersize;
unsigned char encoding;
unsigned char *p;
} zlentry;
二、rpush/lpush 新增元素操作实现
rpush是所尾部添加元素，lpush是从头部添加元素，本质上都是一样的，redis实际上也是完全复用一套代码。
// t_list.c, lpush
void lpushCommand(client *c) {
// 使用 LIST_HEAD|LIST_TAIL 作为插入位置标识
pushGenericCommand(c,LIST_HEAD);
}
void rpushCommand(client *c) {
pushGenericCommand(c,LIST_TAIL);
}
// t_list.c, 实际的push操作
void pushGenericCommand(client *c, int where) {
int j, waiting = 0, pushed = 0;
// 在db中查找对应的key实例，查到或者查不到
robj *lobj = lookupKeyWrite(c->db,c->argv[1]);
// 查到的情况下，需要验证数据类型
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) {
// 1. 在没有key实例的情况下，先创建key实例到db中
lobj = createQuicklistObject();
// 2. 设置 fill和depth 参数
// fill 默认: -2
// depth 默认: 0
quicklistSetOptions(lobj->ptr, server.list_max_ziplist_size,
server.list_compress_depth);
dbAdd(c->db,c->argv[1],lobj);
}
// 3. 一个个元素添加进去
listTypePush(lobj,c->argv[j],where);
pushed++;
}
// 返回list长度
addReplyLongLong(c, waiting + (lobj ? listTypeLength(lobj) : 0));
if (pushed) {
// 命令传播
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;
}
// 1. 创建初始list
// object.c, 创建初始list
robj *createQuicklistObject(void) {
quicklist *l = quicklistCreate();
robj *o = createObject(OBJ_LIST,l);
o->encoding = OBJ_ENCODING_QUICKLIST;
return o;
}
// quicklist.c, 创建一个新的list容器，初始化默认值
/* 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;
}
// 2. 设置quicklist 的fill和depth 值
// quicklist.c
void quicklistSetOptions(quicklist *quicklist, int fill, int depth) {
quicklistSetFill(quicklist, fill);
quicklistSetCompressDepth(quicklist, depth);
}
// quicklist.c, 设置 fill 参数
void quicklistSetFill(quicklist *quicklist, int fill) {
if (fill > FILL_MAX) {
fill = FILL_MAX;
} else if (fill < -5) {
fill = -5;
}
quicklist->fill = fill;
}
// quicklist.c, 设置 depth 参数
void quicklistSetCompressDepth(quicklist *quicklist, int compress) {
if (compress > COMPRESS_MAX) {
compress = COMPRESS_MAX;
} else if (compress < 0) {
compress = 0;
}
quicklist->compress = compress;
}
// 3. 将元素添加进list中
// t_list.c,
/* The function pushes an element to the specified list object 'subject',
* at head or tail position as specified by 'where'.
*
* There is no need for the caller to increment the refcount of 'value' as
* the function takes care of it if needed. */
void listTypePush(robj *subject, robj *value, int where) {
if (subject->encoding == OBJ_ENCODING_QUICKLIST) {
int pos = (where == LIST_HEAD) ? QUICKLIST_HEAD : QUICKLIST_TAIL;
// 解码value
value = getDecodedObject(value);
size_t len = sdslen(value->ptr);
// 将value添加到链表中
quicklistPush(subject->ptr, value->ptr, len, pos);
// 减小value的引用，如果是被解编码后的对象，此时会将内存释放
decrRefCount(value);
} else {
serverPanic("Unknown list encoding");
}
}
// object.c
/* Get a decoded version of an encoded object (returned as a new object).
* If the object is already raw-encoded just increment the ref count. */
robj *getDecodedObject(robj *o) {
robj *dec;
// OBJ_ENCODING_RAW,OBJ_ENCODING_EMBSTR 编码直接返回,引用计数+1(原因是: 原始robj一个引用，转换后的robj一个引用)
if (sdsEncodedObject(o)) {
incrRefCount(o);
return o;
}
if (o->type == OBJ_STRING && o->encoding == OBJ_ENCODING_INT) {
char buf[32];
// 整型转换为字符型，返回string型的robj
ll2string(buf,32,(long)o->ptr);
dec = createStringObject(buf,strlen(buf));
return dec;
} else {
serverPanic("Unknown encoding type");
}
}
// quicklist.c, 添加value到链表中
/* Wrapper to allow argument-based switching between HEAD/TAIL pop */
void quicklistPush(quicklist *quicklist, void *value, const size_t sz,
int where) {
// 根据where决定添加到表头还表尾
if (where == QUICKLIST_HEAD) {
quicklistPushHead(quicklist, value, sz);
} else if (where == QUICKLIST_TAIL) {
quicklistPushTail(quicklist, value, sz);
}
}
// quicklist.c, 添加表头数据
/* Add new entry to head node of quicklist.
*
* Returns 0 if used existing head.
* Returns 1 if new head created. */
int quicklistPushHead(quicklist *quicklist, void *value, size_t sz) {
quicklistNode *orig_head = quicklist->head;
// likely 对不同平台处理 __builtin_expect(!!(x), 1),
// 判断是否允许插入元素,实际上是判断 head 的ziplist空间是否已占满, 没有则直接往里面插入即可
// fill 默认: -2
// depth 默认: 0
if (likely(
_quicklistNodeAllowInsert(quicklist->head, quicklist->fill, sz))) {
// 3.1. 添加head节点的zl链表中, zl 为ziplist 链表节点
quicklist->head->zl =
ziplistPush(quicklist->head->zl, value, sz, ZIPLIST_HEAD);
// 3.2. 更新头节点size大小
quicklistNodeUpdateSz(quicklist->head);
} else {
// 如果head已占满，则创建一个新的 quicklistNode 节点进行插入
quicklistNode *node = quicklistCreateNode();
node->zl = ziplistPush(ziplistNew(), value, sz, ZIPLIST_HEAD);
quicklistNodeUpdateSz(node);
// 3.3. 插入新节点到head之前
_quicklistInsertNodeBefore(quicklist, quicklist->head, node);
}
// 将链表计数+1, 避免获取总数时迭代计算
quicklist->count++;
quicklist->head->count++;
return (orig_head != quicklist->head);
}
// quicklist.c, 判断是否允许插入元素
REDIS_STATIC int _quicklistNodeAllowInsert(const quicklistNode *node,
const int fill, const size_t sz) {
if (unlikely(!node))
return 0;
int ziplist_overhead;
/* size of previous offset */
if (sz < 254)
ziplist_overhead = 1;
else
ziplist_overhead = 5;
/* size of forward offset */
if (sz < 64)
ziplist_overhead += 1;
else if (likely(sz < 16384))
ziplist_overhead += 2;
else
ziplist_overhead += 5;
/* new_sz overestimates if 'sz' encodes to an integer type */
// 加上需要添加的新元素的长度后，进行阀值判定，如果在阀值内，则返回1，否则返回0
unsigned int new_sz = node->sz + sz + ziplist_overhead;
// 使用fill参数判定
if (likely(_quicklistNodeSizeMeetsOptimizationRequirement(new_sz, fill)))
return 1;
else if (!sizeMeetsSafetyLimit(new_sz))
return 0;
else if ((int)node->count < fill)
return 1;
else
return 0;
}
// quicklist.c
REDIS_STATIC int
_quicklistNodeSizeMeetsOptimizationRequirement(const size_t sz,
const int fill) {
if (fill >= 0)
return 0;
size_t offset = (-fill) - 1;
// /* Optimization levels for size-based filling */
// static const size_t optimization_level[] = {4096, 8192, 16384, 32768, 65536};
// offset < 5, offset 默认将等于 1, sz <= 8292
if (offset < (sizeof(optimization_level) / sizeof(*optimization_level))) {
if (sz <= optimization_level[offset]) {
return 1;
} else {
return 0;
}
} else {
return 0;
}
}
// SIZE_SAFETY_LIMIT 8192
#define sizeMeetsSafetyLimit(sz) ((sz) <= SIZE_SAFETY_LIMIT)
// 3.1. 向每个链表节点中添加value, 实际是向 ziplist push 数据
// ziplist.c, push *s 数据到 zl 中
unsigned char *ziplistPush(unsigned char *zl, unsigned char *s, unsigned int slen, int where) {
unsigned char *p;
p = (where == ZIPLIST_HEAD) ? ZIPLIST_ENTRY_HEAD(zl) : ZIPLIST_ENTRY_END(zl);
// 具体添加元素方法，有点复杂。简单点说就是 判断容量、扩容、按照ziplist协议添加元素
return __ziplistInsert(zl,p,s,slen);
}
// ziplist.c, 在hash的数据介绍时已详细介绍
/* Insert item at "p". */
static unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
size_t curlen = intrev32ifbe(ZIPLIST_BYTES(zl)), reqlen;
unsigned int prevlensize, prevlen = 0;
size_t offset;
int nextdiff = 0;
unsigned char encoding = 0;
long long value = 123456789; /* initialized to avoid warning. Using a value
that is easy to see if for some reason
we use it uninitialized. */
zlentry tail;
/* Find out prevlen for the entry that is inserted. */
if (p[0] != ZIP_END) {
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
} else {
unsigned char *ptail = ZIPLIST_ENTRY_TAIL(zl);
if (ptail[0] != ZIP_END) {
prevlen = zipRawEntryLength(ptail);
}
}
/* See if the entry can be encoded */
if (zipTryEncoding(s,slen,&value,&encoding)) {
/* 'encoding' is set to the appropriate integer encoding */
reqlen = zipIntSize(encoding);
} else {
/* 'encoding' is untouched, however zipEncodeLength will use the
* string length to figure out how to encode it. */
reqlen = slen;
}
/* We need space for both the length of the previous entry and
* the length of the payload. */
reqlen += zipPrevEncodeLength(NULL,prevlen);
reqlen += zipEncodeLength(NULL,encoding,slen);
/* When the insert position is not equal to the tail, we need to
* make sure that the next entry can hold this entry's length in
* its prevlen field. */
nextdiff = (p[0] != ZIP_END) ? zipPrevLenByteDiff(p,reqlen) : 0;
/* Store offset because a realloc may change the address of zl. */
offset = p-zl;
zl = ziplistResize(zl,curlen+reqlen+nextdiff);
p = zl+offset;
/* Apply memory move when necessary and update tail offset. */
if (p[0] != ZIP_END) {
/* Subtract one because of the ZIP_END bytes */
memmove(p+reqlen,p-nextdiff,curlen-offset-1+nextdiff);
/* Encode this entry's raw length in the next entry. */
zipPrevEncodeLength(p+reqlen,reqlen);
/* Update offset for tail */
ZIPLIST_TAIL_OFFSET(zl) =
intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+reqlen);
/* When the tail contains more than one entry, we need to take
* "nextdiff" in account as well. Otherwise, a change in the
* size of prevlen doesn't have an effect on the *tail* offset. */
zipEntry(p+reqlen, &tail);
if (p[reqlen+tail.headersize+tail.len] != ZIP_END) {
ZIPLIST_TAIL_OFFSET(zl) =
intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+nextdiff);
}
} else {
/* This element will be the new tail. */
ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(p-zl);
}
/* When nextdiff != 0, the raw length of the next entry has changed, so
* we need to cascade the update throughout the ziplist */
if (nextdiff != 0) {
offset = p-zl;
zl = __ziplistCascadeUpdate(zl,p+reqlen);
p = zl+offset;
}
/* Write the entry */
p += zipPrevEncodeLength(p,prevlen);
p += zipEncodeLength(p,encoding,slen);
if (ZIP_IS_STR(encoding)) {
memcpy(p,s,slen);
} else {
zipSaveInteger(p,value,encoding);
}
ZIPLIST_INCR_LENGTH(zl,1);
return zl;
}
// 3.2. 更新node的size （实际占用内存空间大小）
// quicklist.c, 更新node的size, 其实就是重新统计node的ziplist长度
#define quicklistNodeUpdateSz(node) \
do { \
(node)->sz = ziplistBlobLen((node)->zl); \
} while (0)
// 3.3. 添加新链表节点到head之前
// quicklist.c,
/* Wrappers for node inserting around existing node. */
REDIS_STATIC void _quicklistInsertNodeBefore(quicklist *quicklist,
quicklistNode *old_node,
quicklistNode *new_node) {
__quicklistInsertNode(quicklist, old_node, new_node, 0);
}
/* Insert 'new_node' after 'old_node' if 'after' is 1.
* Insert 'new_node' before 'old_node' if 'after' is 0.
* Note: 'new_node' is *always* uncompressed, so if we assign it to
* head or tail, we do not need to uncompress it. */
REDIS_STATIC void __quicklistInsertNode(quicklist *quicklist,
quicklistNode *old_node,
quicklistNode *new_node, int after) {
if (after) {
new_node->prev = old_node;
if (old_node) {
new_node->next = old_node->next;
if (old_node->next)
old_node->next->prev = new_node;
old_node->next = new_node;
}
if (quicklist->tail == old_node)
quicklist->tail = new_node;
} else {
// 插入new_node到old_node之前
new_node->next = old_node;
if (old_node) {
new_node->prev = old_node->prev;
if (old_node->prev)
old_node->prev->next = new_node;
old_node->prev = new_node;
}
// 替换头节点位置
if (quicklist->head == old_node)
quicklist->head = new_node;
}
/* If this insert creates the only element so far, initialize head/tail. */
// 第一个元素
if (quicklist->len == 0) {
quicklist->head = quicklist->tail = new_node;
}
// 压缩list
if (old_node)
quicklistCompress(quicklist, old_node);
quicklist->len++;
}
// quicklist.c, 压缩list
#define quicklistCompress(_ql, _node) \
do { \
if ((_node)->recompress) \
// recompress
quicklistCompressNode((_node)); \
else \
//
__quicklistCompress((_ql), (_node)); \
} while (0)
// recompress
/* Compress only uncompressed nodes. */
#define quicklistCompressNode(_node) \
do { \
if ((_node) && (_node)->encoding == QUICKLIST_NODE_ENCODING_RAW) { \
__quicklistCompressNode((_node)); \
} \
} while (0)
/* Compress the ziplist in 'node' and update encoding details.
* Returns 1 if ziplist compressed successfully.
* Returns 0 if compression failed or if ziplist too small to compress. */
REDIS_STATIC int __quicklistCompressNode(quicklistNode *node) {
#ifdef REDIS_TEST
node->attempted_compress = 1;
#endif
/* Don't bother compressing small values */
if (node->sz < MIN_COMPRESS_BYTES)
return 0;
quicklistLZF *lzf = zmalloc(sizeof(*lzf) + node->sz);
/* Cancel if compression fails or doesn't compress small enough */
// lzf 压缩算法，有点复杂咯
if (((lzf->sz = lzf_compress(node->zl, node->sz, lzf->compressed,
node->sz)) == 0) ||
lzf->sz + MIN_COMPRESS_IMPROVE >= node->sz) {
/* lzf_compress aborts/rejects compression if value not compressable. */
zfree(lzf);
return 0;
}
lzf = zrealloc(lzf, sizeof(*lzf) + lzf->sz);
zfree(node->zl);
node->zl = (unsigned char *)lzf;
node->encoding = QUICKLIST_NODE_ENCODING_LZF;
node->recompress = 0;
return 1;
}
/* Force 'quicklist' to meet compression guidelines set by compress depth.
* The only way to guarantee interior nodes get compressed is to iterate
* to our "interior" compress depth then compress the next node we find.
* If compress depth is larger than the entire list, we return immediately. */
REDIS_STATIC void __quicklistCompress(const quicklist *quicklist,
quicklistNode *node) {
/* If length is less than our compress depth (from both sides),
* we can't compress anything. */
if (!quicklistAllowsCompression(quicklist) ||
quicklist->len < (unsigned int)(quicklist->compress * 2))
return;
#if 0
/* Optimized cases for small depth counts */
if (quicklist->compress == 1) {
quicklistNode *h = quicklist->head, *t = quicklist->tail;
quicklistDecompressNode(h);
quicklistDecompressNode(t);
if (h != node && t != node)
quicklistCompressNode(node);
return;
} else if (quicklist->compress == 2) {
quicklistNode *h = quicklist->head, *hn = h->next, *hnn = hn->next;
quicklistNode *t = quicklist->tail, *tp = t->prev, *tpp = tp->prev;
quicklistDecompressNode(h);
quicklistDecompressNode(hn);
quicklistDecompressNode(t);
quicklistDecompressNode(tp);
if (h != node && hn != node && t != node && tp != node) {
quicklistCompressNode(node);
}
if (hnn != t) {
quicklistCompressNode(hnn);
}
if (tpp != h) {
quicklistCompressNode(tpp);
}
return;
}
#endif
/* Iterate until we reach compress depth for both sides of the list.a
* Note: because we do length checks at the *top* of this function,
* we can skip explicit null checks below. Everything exists. */
quicklistNode *forward = quicklist->head;
quicklistNode *reverse = quicklist->tail;
int depth = 0;
int in_depth = 0;
while (depth++ < quicklist->compress) {
// 解压缩？？？
quicklistDecompressNode(forward);
quicklistDecompressNode(reverse);
if (forward == node || reverse == node)
in_depth = 1;
if (forward == reverse)
return;
forward = forward->next;
reverse = reverse->prev;
}
if (!in_depth)
quicklistCompressNode(node);
if (depth > 2) {
/* At this point, forward and reverse are one node beyond depth */
// 压缩
quicklistCompressNode(forward);
quicklistCompressNode(reverse);
}
}
/* Decompress only compressed nodes. */
#define quicklistDecompressNode(_node) \
do { \
if ((_node) && (_node)->encoding == QUICKLIST_NODE_ENCODING_LZF) { \
__quicklistDecompressNode((_node)); \
} \
} while (0)
/* Uncompress the ziplist in 'node' and update encoding details.
* Returns 1 on successful decode, 0 on failure to decode. */
REDIS_STATIC int __quicklistDecompressNode(quicklistNode *node) {
#ifdef REDIS_TEST
node->attempted_compress = 0;
#endif
void *decompressed = zmalloc(node->sz);
quicklistLZF *lzf = (quicklistLZF *)node->zl;
if (lzf_decompress(lzf->compressed, lzf->sz, decompressed, node->sz) == 0) {
/* Someone requested decompress, but we can't decompress. Not good. */
zfree(decompressed);
return 0;
}
zfree(lzf);
node->zl = decompressed;
node->encoding = QUICKLIST_NODE_ENCODING_RAW;
return 1;
}
总体来说，redis的list实现不是纯粹的单双向链表，而是 使用双向链表+ziplist 的方式实现链表功能，既节省了内存空间，对于查找来说时间复杂度也相对小。我们用一个时序图来重新审视下：
三、lindex/lrange/rrange 查找操作
读数据是数据库的一个另一个重要功能。一般来说，有单个查询，批量查询，范围查询之类的功能，咱们就分头说说。
// 1. 单个查询 lindex key index
// t_list.c, 通过下标查找元素值
void lindexCommand(client *c) {
robj *o = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk);
// 如果key本身就不存在，直接返回，空已响应
if (o == NULL || checkType(c,o,OBJ_LIST)) return;
long index;
robj *value = NULL;
// 解析index字段，赋给 index 变量
if ((getLongFromObjectOrReply(c, c->argv[2], &index, NULL) != C_OK))
return;
if (o->encoding == OBJ_ENCODING_QUICKLIST) {
quicklistEntry entry;
// 根据index查询list数据
if (quicklistIndex(o->ptr, index, &entry)) {
// 使用两个字段来保存value
if (entry.value) {
value = createStringObject((char*)entry.value,entry.sz);
} else {
value = createStringObjectFromLongLong(entry.longval);
}
addReplyBulk(c,value);
decrRefCount(value);
} else {
addReply(c,shared.nullbulk);
}
} else {
serverPanic("Unknown list encoding");
}
}
// quicklist.c, 根据 index 查找元素
/* Populate 'entry' with the element at the specified zero-based index
* where 0 is the head, 1 is the element next to head
* and so on. Negative integers are used in order to count
* from the tail, -1 is the last element, -2 the penultimate
* and so on. If the index is out of range 0 is returned.
*
* Returns 1 if element found
* Returns 0 if element not found */
int quicklistIndex(const quicklist *quicklist, const long long idx,
quicklistEntry *entry) {
quicklistNode *n;
unsigned long long accum = 0;
unsigned long long index;
int forward = idx < 0 ? 0 : 1; /* < 0 -> reverse, 0+ -> forward */
// 初始化 quicklistEntry, 设置默认值
initEntry(entry);
entry->quicklist = quicklist;
// index为负数时，逆向搜索
if (!forward) {
index = (-idx) - 1;
n = quicklist->tail;
} else {
index = idx;
n = quicklist->head;
}
if (index >= quicklist->count)
return 0;
while (likely(n)) {
// n->count 代表每个list节点里的实际元素的个数（ziplist里可能包含n个元素）
// 此处代表只会迭代到 index 所在的list节点就停止了
if ((accum + n->count) > index) {
break;
} else {
D("Skipping over (%p) %u at accum %lld", (void *)n, n->count,
accum);
// 依次迭代
accum += n->count;
n = forward ? n->next : n->prev;
}
}
// 如果已经迭代完成，说明未找到index元素
if (!n)
return 0;
D("Found node: %p at accum %llu, idx %llu, sub+ %llu, sub- %llu", (void *)n,
accum, index, index - accum, (-index) - 1 + accum);
entry->node = n;
if (forward) {
/* forward = normal head-to-tail offset. */
// index-accum 代表index节点在 当前n节点中的偏移
entry->offset = index - accum;
} else {
/* reverse = need negative offset for tail-to-head, so undo
* the result of the original if (index < 0) above. */
// 逆向搜索定位 如-1=1-1+0,-2=2-1+0
entry->offset = (-index) - 1 + accum;
}
// 解压缩node数据
quicklistDecompressNodeForUse(entry->node);
// 根据offset，查找ziplist中的sds value
entry->zi = ziplistIndex(entry->node->zl, entry->offset);
// 从zi中获取value,sz,longval 返回 (ziplist 协议)
ziplistGet(entry->zi, &entry->value, &entry->sz, &entry->longval);
/* The caller will use our result, so we don't re-compress here.
* The caller can recompress or delete the node as needed. */
return 1;
}
// quicklist.c
/* Simple way to give quicklistEntry structs default values with one call. */
#define initEntry(e) \
do { \
(e)->zi = (e)->value = NULL; \
(e)->longval = -123456789; \
(e)->quicklist = NULL; \
(e)->node = NULL; \
(e)->offset = 123456789; \
(e)->sz = 0; \
} while (0)
// 解压缩node数据
/* Force node to not be immediately re-compresable */
#define quicklistDecompressNodeForUse(_node) \
do { \
if ((_node) && (_node)->encoding == QUICKLIST_NODE_ENCODING_LZF) { \
__quicklistDecompressNode((_node)); \
(_node)->recompress = 1; \
} \
} while (0)
/* Uncompress the ziplist in 'node' and update encoding details.
* Returns 1 on successful decode, 0 on failure to decode. */
REDIS_STATIC int __quicklistDecompressNode(quicklistNode *node) {
#ifdef REDIS_TEST
node->attempted_compress = 0;
#endif
void *decompressed = zmalloc(node->sz);
quicklistLZF *lzf = (quicklistLZF *)node->zl;
if (lzf_decompress(lzf->compressed, lzf->sz, decompressed, node->sz) == 0) {
/* Someone requested decompress, but we can't decompress. Not good. */
zfree(decompressed);
return 0;
}
zfree(lzf);
node->zl = decompressed;
node->encoding = QUICKLIST_NODE_ENCODING_RAW;
return 1;
}
// ziplist.c
/* Returns an offset to use for iterating with ziplistNext. When the given
* index is negative, the list is traversed back to front. When the list
* doesn't contain an element at the provided index, NULL is returned. */
unsigned char *ziplistIndex(unsigned char *zl, int index) {
unsigned char *p;
unsigned int prevlensize, prevlen = 0;
if (index < 0) {
index = (-index)-1;
p = ZIPLIST_ENTRY_TAIL(zl);
if (p[0] != ZIP_END) {
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
while (prevlen > 0 && index--) {
p -= prevlen;
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
}
}
} else {
p = ZIPLIST_ENTRY_HEAD(zl);
while (p[0] != ZIP_END && index--) {
p += zipRawEntryLength(p);
}
}
return (p[0] == ZIP_END || index > 0) ? NULL : p;
}
对于范围查找来说，按照redis之前的套路，有可能是在单个查找的上面再进行循环查找就可以了，是否是这样呢？我们来看看：
// 2. lrange 范围查询
// t_list.c
void lrangeCommand(client *c) {
robj *o;
long start, end, llen, rangelen;
// 解析 start,end 参数
if ((getLongFromObjectOrReply(c, c->argv[2], &start, NULL) != C_OK) ||
(getLongFromObjectOrReply(c, c->argv[3], &end, NULL) != C_OK)) return;
if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk)) == NULL
|| checkType(c,o,OBJ_LIST)) return;
// list 长度获取, 有个计数器在
llen = listTypeLength(o);
/* convert negative indexes */
if (start < 0) start = llen+start;
if (end < 0) end = llen+end;
// 将-xx的下标转换为正数查询，如果负数过大，则以0计算
if (start < 0) start = 0;
/* Invariant: start >= 0, so this test will be true when end < 0.
* The range is empty when start > end or start >= length. */
if (start > end || start >= llen) {
addReply(c,shared.emptymultibulk);
return;
}
// end 过大，则限制
// end 不可能小于0，因为上一个 start > end 已限制
if (end >= llen) end = llen-1;
rangelen = (end-start)+1;
/* Return the result in form of a multi-bulk reply */
addReplyMultiBulkLen(c,rangelen);
if (o->encoding == OBJ_ENCODING_QUICKLIST) {
// 返回列表迭代器, start-TAIL, LIST_TAIL 代表正向迭代
listTypeIterator *iter = listTypeInitIterator(o, start, LIST_TAIL);
// 迭代到 rangelen=0 为止，依次向输出缓冲输出
while(rangelen--) {
listTypeEntry entry;
// 获取下一个元素
listTypeNext(iter, &entry);
quicklistEntry *qe = &entry.entry;
if (qe->value) {
addReplyBulkCBuffer(c,qe->value,qe->sz);
} else {
addReplyBulkLongLong(c,qe->longval);
}
}
listTypeReleaseIterator(iter);
} else {
serverPanic("List encoding is not QUICKLIST!");
}
}
// t_list.c, 统计list长度
unsigned long listTypeLength(robj *subject) {
if (subject->encoding == OBJ_ENCODING_QUICKLIST) {
return quicklistCount(subject->ptr);
} else {
serverPanic("Unknown list encoding");
}
}
/* Return cached quicklist count */
unsigned int quicklistCount(quicklist *ql) { return ql->count; }
// 初始化 list 迭代器
/* Initialize an iterator at the specified index. */
listTypeIterator *listTypeInitIterator(robj *subject, long index,
unsigned char direction) {
listTypeIterator *li = zmalloc(sizeof(listTypeIterator));
li->subject = subject;
li->encoding = subject->encoding;
li->direction = direction;
li->iter = NULL;
/* LIST_HEAD means start at TAIL and move *towards* head.
* LIST_TAIL means start at HEAD and move *towards tail. */
int iter_direction =
direction == LIST_HEAD ? AL_START_TAIL : AL_START_HEAD;
if (li->encoding == OBJ_ENCODING_QUICKLIST) {
li->iter = quicklistGetIteratorAtIdx(li->subject->ptr,
iter_direction, index);
} else {
serverPanic("Unknown list encoding");
}
return li;
}
/* Initialize an iterator at a specific offset 'idx' and make the iterator
* return nodes in 'direction' direction. */
quicklistIter *quicklistGetIteratorAtIdx(const quicklist *quicklist,
const int direction,
const long long idx) {
quicklistEntry entry;
// 查找idx 元素先 （前面已介绍, 为 ziplist+quicklist 迭代获得）
if (quicklistIndex(quicklist, idx, &entry)) {
// 获取获取的是整个list的迭代器, 通过current和offset进行迭代
quicklistIter *base = quicklistGetIterator(quicklist, direction);
base->zi = NULL;
base->current = entry.node;
base->offset = entry.offset;
return base;
} else {
return NULL;
}
}
// quicklist, list迭代器初始化
/* Returns a quicklist iterator 'iter'. After the initialization every
* call to quicklistNext() will return the next element of the quicklist. */
quicklistIter *quicklistGetIterator(const quicklist *quicklist, int direction) {
quicklistIter *iter;
// 迭代器只包含当前元素
iter = zmalloc(sizeof(*iter));
if (direction == AL_START_HEAD) {
iter->current = quicklist->head;
iter->offset = 0;
} else if (direction == AL_START_TAIL) {
iter->current = quicklist->tail;
iter->offset = -1;
}
iter->direction = direction;
iter->quicklist = quicklist;
iter->zi = NULL;
return iter;
}
// 迭代器携带整个list 引用，及当前节点，如何进行迭代，则是重点
// t_list.c, 迭代list元素, 并将 当前节点赋给 entry
/* Stores pointer to current the entry in the provided entry structure
* and advances the position of the iterator. Returns 1 when the current
* entry is in fact an entry, 0 otherwise. */
int listTypeNext(listTypeIterator *li, listTypeEntry *entry) {
/* Protect from converting when iterating */
serverAssert(li->subject->encoding == li->encoding);
entry->li = li;
if (li->encoding == OBJ_ENCODING_QUICKLIST) {
// 迭代iter(改变iter指向), 赋值给 entry->entry
return quicklistNext(li->iter, &entry->entry);
} else {
serverPanic("Unknown list encoding");
}
return 0;
}
// quicklist.c
/* Get next element in iterator.
*
* Note: You must NOT insert into the list while iterating over it.
* You *may* delete from the list while iterating using the
* quicklistDelEntry() function.
* If you insert into the quicklist while iterating, you should
* re-create the iterator after your addition.
*
* iter = quicklistGetIterator(quicklist,<direction>);
* quicklistEntry entry;
* while (quicklistNext(iter, &entry)) {
* if (entry.value)
* [[ use entry.value with entry.sz ]]
* else
* [[ use entry.longval ]]
* }
*
* Populates 'entry' with values for this iteration.
* Returns 0 when iteration is complete or if iteration not possible.
* If return value is 0, the contents of 'entry' are not valid.
*/
int quicklistNext(quicklistIter *iter, quicklistEntry *entry) {
initEntry(entry);
if (!iter) {
D("Returning because no iter!");
return 0;
}
// 保存当前node, 及quicklist引用
entry->quicklist = iter->quicklist;
entry->node = iter->current;
if (!iter->current) {
D("Returning because current node is NULL")
return 0;
}
unsigned char *(*nextFn)(unsigned char *, unsigned char *) = NULL;
int offset_update = 0;
if (!iter->zi) {
/* If !zi, use current index. */
// 初始化时 zi 未赋值，所以直接使用当前元素，使用offset进行查找
quicklistDecompressNodeForUse(iter->current);
iter->zi = ziplistIndex(iter->current->zl, iter->offset);
} else {
/* else, use existing iterator offset and get prev/next as necessary. */
if (iter->direction == AL_START_HEAD) {
nextFn = ziplistNext;
offset_update = 1;
} else if (iter->direction == AL_START_TAIL) {
nextFn = ziplistPrev;
offset_update = -1;
}
// 向前或向后迭代元素
iter->zi = nextFn(iter->current->zl, iter->zi);
iter->offset += offset_update;
}
entry->zi = iter->zi;
entry->offset = iter->offset;
if (iter->zi) {
/* Populate value from existing ziplist position */
// 从 zi 中获取值返回 （按ziplist协议）
ziplistGet(entry->zi, &entry->value, &entry->sz, &entry->longval);
return 1;
} else {
/* We ran out of ziplist entries.
* Pick next node, update offset, then re-run retrieval. */
// 当前ziplist没有下一个元素了，递归查找下一个ziplist
quicklistCompress(iter->quicklist, iter->current);
if (iter->direction == AL_START_HEAD) {
/* Forward traversal */
D("Jumping to start of next node");
iter->current = iter->current->next;
iter->offset = 0;
} else if (iter->direction == AL_START_TAIL) {
/* Reverse traversal */
D("Jumping to end of previous node");
iter->current = iter->current->prev;
iter->offset = -1;
}
iter->zi = NULL;
return quicklistNext(iter, entry);
}
}
// ziplist.c
/* Get entry pointed to by 'p' and store in either '*sstr' or 'sval' depending
* on the encoding of the entry. '*sstr' is always set to NULL to be able
* to find out whether the string pointer or the integer value was set.
* Return 0 if 'p' points to the end of the ziplist, 1 otherwise. */
unsigned int ziplistGet(unsigned char *p, unsigned char **sstr, unsigned int *slen, long long *sval) {
zlentry entry;
if (p == NULL || p[0] == ZIP_END) return 0;
if (sstr) *sstr = NULL;
zipEntry(p, &entry);
if (ZIP_IS_STR(entry.encoding)) {
if (sstr) {
*slen = entry.len;
*sstr = p+entry.headersize;
}
} else {
if (sval) {
*sval = zipLoadInteger(p+entry.headersize,entry.encoding);
}
}
return 1;
}
看起来并没有利用单个查找的代码，而是使用迭代器进行操作。看起来不难，但是有点绕，我们就用一个时序图来重新表达下：
四、lrem 删除操作
增删改查，还是要凑够的。删除的操作，自然是要配置数据结构来做了，比如: 如何定位要删除的元素，删除后链表是否需要重排？
// LREM key count value, 只提供了范围删除的方式，单个数据删除可以通过此命令来完成
// t_list.c
void lremCommand(client *c) {
robj *subject, *obj;
obj = c->argv[3];
long toremove;
long removed = 0;
if ((getLongFromObjectOrReply(c, c->argv[2], &toremove, NULL) != C_OK))
return;
subject = lookupKeyWriteOrReply(c,c->argv[1],shared.czero);
if (subject == NULL || checkType(c,subject,OBJ_LIST)) return;
// 因是范围型删除，自然使用迭代删除是最好的选择了
listTypeIterator *li;
if (toremove < 0) {
toremove = -toremove;
li = listTypeInitIterator(subject,-1,LIST_HEAD);
} else {
li = listTypeInitIterator(subject,0,LIST_TAIL);
}
listTypeEntry entry;
// 迭代方式我们在查找操作已详细说明
while (listTypeNext(li,&entry)) {
// 1. 比较元素是否是需要删除的对象，只有完全匹配才可以删除
if (listTypeEqual(&entry,obj)) {
// 2. 实际的删除动作
listTypeDelete(li, &entry);
server.dirty++;
removed++;
if (toremove && removed == toremove) break;
}
}
listTypeReleaseIterator(li);
// 如果没有任何元素后，将key从db中删除
if (listTypeLength(subject) == 0) {
dbDelete(c->db,c->argv[1]);
}
addReplyLongLong(c,removed);
if (removed) signalModifiedKey(c->db,c->argv[1]);
}
// 1. 是否与指定robj相等
// t_list.c, listTypeEntry 是否与指定robj相等
/* Compare the given object with the entry at the current position. */
int listTypeEqual(listTypeEntry *entry, robj *o) {
if (entry->li->encoding == OBJ_ENCODING_QUICKLIST) {
serverAssertWithInfo(NULL,o,sdsEncodedObject(o));
return quicklistCompare(entry->entry.zi,o->ptr,sdslen(o->ptr));
} else {
serverPanic("Unknown list encoding");
}
}
// t_list.c
int quicklistCompare(unsigned char *p1, unsigned char *p2, int p2_len) {
// 元素本身是 ziplist 类型的，所以直接交由ziplist比对即可
return ziplistCompare(p1, p2, p2_len);
}
// ziplist.c
/* Compare entry pointer to by 'p' with 'sstr' of length 'slen'. */
/* Return 1 if equal. */
unsigned int ziplistCompare(unsigned char *p, unsigned char *sstr, unsigned int slen) {
zlentry entry;
unsigned char sencoding;
long long zval, sval;
if (p[0] == ZIP_END) return 0;
zipEntry(p, &entry);
if (ZIP_IS_STR(entry.encoding)) {
/* Raw compare */
if (entry.len == slen) {
return memcmp(p+entry.headersize,sstr,slen) == 0;
} else {
return 0;
}
} else {
/* Try to compare encoded values. Don't compare encoding because
* different implementations may encoded integers differently. */
if (zipTryEncoding(sstr,slen,&sval,&sencoding)) {
zval = zipLoadInteger(p+entry.headersize,entry.encoding);
return zval == sval;
}
}
return 0;
}
/* Delete the element pointed to. */
void listTypeDelete(listTypeIterator *iter, listTypeEntry *entry) {
if (entry->li->encoding == OBJ_ENCODING_QUICKLIST) {
quicklistDelEntry(iter->iter, &entry->entry);
} else {
serverPanic("Unknown list encoding");
}
}
// 2. 执行删除操作
// t_list.c
/* Delete the element pointed to. */
void listTypeDelete(listTypeIterator *iter, listTypeEntry *entry) {
if (entry->li->encoding == OBJ_ENCODING_QUICKLIST) {
quicklistDelEntry(iter->iter, &entry->entry);
} else {
serverPanic("Unknown list encoding");
}
}
// quicklist.c
/* Delete one element represented by 'entry'
*
* 'entry' stores enough metadata to delete the proper position in
* the correct ziplist in the correct quicklist node. */
void quicklistDelEntry(quicklistIter *iter, quicklistEntry *entry) {
quicklistNode *prev = entry->node->prev;
quicklistNode *next = entry->node->next;
int deleted_node = quicklistDelIndex((quicklist *)entry->quicklist,
entry->node, &entry->zi);
/* after delete, the zi is now invalid for any future usage. */
iter->zi = NULL;
/* If current node is deleted, we must update iterator node and offset. */
if (deleted_node) {
// 如果node被删除，则移动quicklist指针
if (iter->direction == AL_START_HEAD) {
iter->current = next;
iter->offset = 0;
} else if (iter->direction == AL_START_TAIL) {
iter->current = prev;
iter->offset = -1;
}
}
/* else if (!deleted_node), no changes needed.
* we already reset iter->zi above, and the existing iter->offset
* doesn't move again because:
* - [1, 2, 3] => delete offset 1 => [1, 3]: next element still offset 1
* - [1, 2, 3] => delete offset 0 => [2, 3]: next element still offset 0
* if we deleted the last element at offet N and now
* length of this ziplist is N-1, the next call into
* quicklistNext() will jump to the next node. */
}
// quicklist.c
/* 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. */
REDIS_STATIC int quicklistDelIndex(quicklist *quicklist, quicklistNode *node,
unsigned char **p) {
int gone = 0;
// 同样，到最后一级，依旧是调用ziplist的方法进行删除 (按照 ziplist 协议操作即可)
node->zl = ziplistDelete(node->zl, p);
node->count--;
// 如果node中没有元素了，就把当前node移除，否则更新 sz 大小
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;
}
delete 操作总体来说就是一个迭代，比对，删除的操作，细节还是有点多的，只是都是些我们前面说过的技术，也就无所谓了。
五、lpop 弹出队列
这个功能大概和删除的意思差不多，就是删除最后一元素即可。事实上，我们也更喜欢使用redis这种功能。简单看看。
// 用法: LPOP key
// t_list.c
void lpopCommand(client *c) {
popGenericCommand(c,LIST_HEAD);
}
void popGenericCommand(client *c, int where) {
robj *o = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk);
if (o == NULL || checkType(c,o,OBJ_LIST)) return;
// 弹出元素，重点看一下这个方法
robj *value = listTypePop(o,where);
if (value == NULL) {
addReply(c,shared.nullbulk);
} else {
char *event = (where == LIST_HEAD) ? "lpop" : "rpop";
addReplyBulk(c,value);
decrRefCount(value);
notifyKeyspaceEvent(NOTIFY_LIST,event,c->argv[1],c->db->id);
if (listTypeLength(o) == 0) {
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
c->argv[1],c->db->id);
dbDelete(c->db,c->argv[1]);
}
signalModifiedKey(c->db,c->argv[1]);
server.dirty++;
}
}
// t_list.c
robj *listTypePop(robj *subject, int where) {
long long vlong;
robj *value = NULL;
int ql_where = where == LIST_HEAD ? QUICKLIST_HEAD : QUICKLIST_TAIL;
if (subject->encoding == OBJ_ENCODING_QUICKLIST) {
if (quicklistPopCustom(subject->ptr, ql_where, (unsigned char **)&value,
NULL, &vlong, listPopSaver)) {
if (!value)
value = createStringObjectFromLongLong(vlong);
}
} else {
serverPanic("Unknown list encoding");
}
return value;
}
// quicklist.c
/* 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'. */
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;
// 获取ziplist中的，第一个元素或者最后一个节点
if (where == QUICKLIST_HEAD && quicklist->head) {
node = quicklist->head;
} else if (where == QUICKLIST_TAIL && quicklist->tail) {
node = quicklist->tail;
} else {
return 0;
}
// 获取ziplist中的，第一个元素或者最后一个元素
p = ziplistIndex(node->zl, pos);
if (ziplistGet(p, &vstr, &vlen, &vlong)) {
if (vstr) {
if (data)
// 创建string 对象返回
*data = saver(vstr, vlen);
if (sz)
*sz = vlen;
} else {
if (data)
*data = NULL;
if (sval)
*sval = vlong;
}
// 删除获取数据后的元素
quicklistDelIndex(quicklist, node, &p);
return 1;
}
return 0;
}
弹出一个元素，大概分三步：
1. 获取头节点或尾节点;
2. 从ziplist中获取第一个元素或最后一个元素;
3. 删除头节点或尾节点;
六、blpop 阻塞式弹出元素
算是阻塞队列吧。我们只想看一下，像本地语言实现的阻塞，我们知道用锁+wait/notify机制。redis是如何进行阻塞的呢？
// 用法: BLPOP key1 [key2] timeout
// t_list.c 同样 l/r 复用代码
void blpopCommand(client *c) {
blockingPopGenericCommand(c,LIST_HEAD);
}
/* Blocking RPOP/LPOP */
void blockingPopGenericCommand(client *c, int where) {
robj *o;
mstime_t timeout;
int j;
if (getTimeoutFromObjectOrReply(c,c->argv[c->argc-1],&timeout,UNIT_SECONDS)
!= C_OK) return;
// 循环查找多个key
for (j = 1; j < c->argc-1; j++) {
o = lookupKeyWrite(c->db,c->argv[j]);
if (o != NULL) {
if (o->type != OBJ_LIST) {
addReply(c,shared.wrongtypeerr);
return;
} else {
// 如果有值，则和非阻塞版本一样了，直接响应即可
if (listTypeLength(o) != 0) {
/* Non empty list, this is like a non normal [LR]POP. */
char *event = (where == LIST_HEAD) ? "lpop" : "rpop";
robj *value = listTypePop(o,where);
serverAssert(value != NULL);
addReplyMultiBulkLen(c,2);
addReplyBulk(c,c->argv[j]);
addReplyBulk(c,value);
decrRefCount(value);
notifyKeyspaceEvent(NOTIFY_LIST,event,
c->argv[j],c->db->id);
if (listTypeLength(o) == 0) {
dbDelete(c->db,c->argv[j]);
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
c->argv[j],c->db->id);
}
signalModifiedKey(c->db,c->argv[j]);
server.dirty++;
/* Replicate it as an [LR]POP instead of B[LR]POP. */
rewriteClientCommandVector(c,2,
(where == LIST_HEAD) ? shared.lpop : shared.rpop,
c->argv[j]);
// 获取到值后直接结束流程
return;
}
}
}
}
/* If we are inside a MULTI/EXEC and the list is empty the only thing
* we can do is treating it as a timeout (even with timeout 0). */
if (c->flags & CLIENT_MULTI) {
addReply(c,shared.nullmultibulk);
return;
}
/* If the list is empty or the key does not exists we must block */
// 阻塞是在这里实现的
blockForKeys(c, c->argv + 1, c->argc - 2, timeout, NULL);
}
/* This is how the current blocking POP works, we use BLPOP as example:
* - If the user calls BLPOP and the key exists and contains a non empty list
* then LPOP is called instead. So BLPOP is semantically the same as LPOP
* if blocking is not required.
* - If instead BLPOP is called and the key does not exists or the list is
* empty we need to block. In order to do so we remove the notification for
* new data to read in the client socket (so that we'll not serve new
* requests if the blocking request is not served). Also we put the client
* in a dictionary (db->blocking_keys) mapping keys to a list of clients
* blocking for this keys.
* - If a PUSH operation against a key with blocked clients waiting is
* performed, we mark this key as "ready", and after the current command,
* MULTI/EXEC block, or script, is executed, we serve all the clients waiting
* for this list, from the one that blocked first, to the last, accordingly
* to the number of elements we have in the ready list.
*/
/* Set a client in blocking mode for the specified key, with the specified
* timeout */
void blockForKeys(client *c, robj **keys, int numkeys, mstime_t timeout, robj *target) {
dictEntry *de;
list *l;
int j;
c->bpop.timeout = timeout;
c->bpop.target = target;
if (target != NULL) incrRefCount(target);
// 阻塞入队判定
for (j = 0; j < numkeys; j++) {
/* If the key already exists in the dict ignore it. */
if (dictAdd(c->bpop.keys,keys[j],NULL) != DICT_OK) continue;
incrRefCount(keys[j]);
/* And in the other "side", to map keys -> clients */
de = dictFind(c->db->blocking_keys,keys[j]);
if (de == NULL) {
int retval;
/* For every key we take a list of clients blocked for it */
l = listCreate();
// 将阻塞key放到 db 中，后台有线程去轮询
retval = dictAdd(c->db->blocking_keys,keys[j],l);
incrRefCount(keys[j]);
serverAssertWithInfo(c,keys[j],retval == DICT_OK);
} else {
l = dictGetVal(de);
}
// 将每个key 依次添加到 c->db->blocking_keys, 后续迭代将会重新检查取出
listAddNodeTail(l,c);
}
// 阻塞客户端，其实就是设置阻塞标识，然后等待key变更或超时，下一次扫描时将重新检测取出执行
blockClient(c,BLOCKED_LIST);
}
// block.c 设置阻塞标识
/* Block a client for the specific operation type. Once the CLIENT_BLOCKED
* flag is set client query buffer is not longer processed, but accumulated,
* and will be processed when the client is unblocked. */
void blockClient(client *c, int btype) {
c->flags |= CLIENT_BLOCKED;
c->btype = btype;
server.bpop_blocked_clients++;
}
redis阻塞功能的实现: 使用一个 db->blocking_keys 的列表来保存需要阻塞的请求，在下一次循环时，进行扫描这些队列的条件是否满足，从而决定是否继续阻塞或者取出。
思考： 从上面实现中，有个疑问：如何保证最多等待 timeout 时间或者最多循环多少次呢？你觉得应该如何处理呢？
OK, 至此，整个list数据结构的解析算是完整了。
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