redis源码解析（十五）快速链表API功能函数解析
作者：互联网
一. 前言
本文继前文基础上继续分析剩余的快速链表函数源码。
二. 源码分析
/* Replace quicklist entry at offset 'index' by 'data' with length 'sz'.
*
* Returns 1 if replace happened.
* Returns 0 if replace failed and no changes happened. */
int quicklistReplaceAtIndex(quicklist *quicklist, long index, void *data,
int sz) {
quicklistEntry entry;
if (likely(quicklistIndex(quicklist, index, &entry))) {
/* quicklistIndex provides an uncompressed node */
entry.node->zl = ziplistDelete(entry.node->zl, &entry.zi);
entry.node->zl = ziplistInsert(entry.node->zl, entry.zi, data, sz);
quicklistNodeUpdateSz(entry.node);
quicklistCompress(quicklist, entry.node);
return 1;
} else {
return 0;
}
}
/* 融合两个节点的压缩链表，返回融合后的新节点
* Given two nodes, try to merge their ziplists.
*
* This helps us not have a quicklist with 3 element ziplists if
* our fill factor can handle much higher levels.
*
* Note: 'a' must be to the LEFT of 'b'.
*
* After calling this function, both 'a' and 'b' should be considered
* unusable. The return value from this function must be used
* instead of re-using any of the quicklistNode input arguments.
*
* Returns the input node picked to merge against or NULL if
* merging was not possible. */
REDIS_STATIC quicklistNode *_quicklistZiplistMerge(quicklist *quicklist,
quicklistNode *a,
quicklistNode *b) {
D("Requested merge (a,b) (%u, %u)", a->count, b->count);
//展开节点
quicklistDecompressNode(a);
quicklistDecompressNode(b);
//压缩链表融合
if ((ziplistMerge(&a->zl, &b->zl))) {
/* We merged ziplists! Now remove the unused quicklistNode. */
quicklistNode *keep = NULL, *nokeep = NULL;
//根据融合结果选择保留a还是b
if (!a->zl) {
nokeep = a;
keep = b;
} else if (!b->zl) {
nokeep = b;
keep = a;
}
//更新信息
keep->count = ziplistLen(keep->zl);
quicklistNodeUpdateSz(keep);
//删除无用节点，对新节点进行压缩处理
nokeep->count = 0;
__quicklistDelNode(quicklist, nokeep);
quicklistCompress(quicklist, keep);
return keep;
} else {
/* else, the merge returned NULL and nothing changed. */
return NULL;
}
}
/* 对快速链表从中间开始两边分别融合：前2个+中间+后2个融合成1个节点
* Attempt to merge ziplists within two nodes on either side of 'center'.
*
* We attempt to merge:
* - (center->prev->prev, center->prev)
* - (center->next, center->next->next)
* - (center->prev, center)
* - (center, center->next)
*/
REDIS_STATIC void _quicklistMergeNodes(quicklist *quicklist,
quicklistNode *center) {
int fill = quicklist->fill;
quicklistNode *prev, *prev_prev, *next, *next_next, *target;
prev = prev_prev = next = next_next = target = NULL;
//获取前向节点
if (center->prev) {
prev = center->prev;
if (center->prev->prev)
prev_prev = center->prev->prev;
}
//获取后向节点
if (center->next) {
next = center->next;
if (center->next->next)
next_next = center->next->next;
}
/* 尝试前向节点融合
* Try to merge prev_prev and prev
*/
if (_quicklistNodeAllowMerge(prev, prev_prev, fill)) {
_quicklistZiplistMerge(quicklist, prev_prev, prev);
prev_prev = prev = NULL; /* they could have moved, invalidate them. */
}
/* 尝试后向节点融合
* Try to merge next and next_next
*/
if (_quicklistNodeAllowMerge(next, next_next, fill)) {
_quicklistZiplistMerge(quicklist, next, next_next);
next = next_next = NULL; /* they could have moved, invalidate them. */
}
/* 中间节点和前向进行融合
* Try to merge center node and previous node
*/
if (_quicklistNodeAllowMerge(center, center->prev, fill)) {
target = _quicklistZiplistMerge(quicklist, center->prev, center);
center = NULL; /* center could have been deleted, invalidate it. */
} else {
/* else, we didn't merge here, but target needs to be valid below. */
target = center;
}
/* 和后向新节点进行融合
* Use result of center merge (or original) to merge with next node.
*/
if (_quicklistNodeAllowMerge(target, target->next, fill)) {
_quicklistZiplistMerge(quicklist, target, target->next);
}
}
/* 根据offset和after分割快速链表的节点
* after为1则返回包含从offset到结尾的值的节点，0到offset的值保存在传参指针node中
* after为0则刚好相反
* Split 'node' into two parts, parameterized by 'offset' and 'after'.
*
* The 'after' argument controls which quicklistNode gets returned.
* If 'after'==1, returned node has elements after 'offset'.
* input node keeps elements up to 'offset', including 'offset'.
* If 'after'==0, returned node has elements up to 'offset', including 'offset'.
* input node keeps elements after 'offset'.
*
* If 'after'==1, returned node will have elements _after_ 'offset'.
* The returned node will have elements [OFFSET+1, END].
* The input node keeps elements [0, OFFSET].
*
* If 'after'==0, returned node will keep elements up to and including 'offset'.
* The returned node will have elements [0, OFFSET].
* The input node keeps elements [OFFSET+1, END].
*
* The input node keeps all elements not taken by the returned node.
*
* Returns newly created node or NULL if split not possible. */
REDIS_STATIC quicklistNode *_quicklistSplitNode(quicklistNode *node, int offset,
int after) {
//获取压缩链表的大小
size_t zl_sz = node->sz;
//创建新快速链表节点保存
quicklistNode *new_node = quicklistCreateNode();
new_node->zl = zmalloc(zl_sz);
/* 拷贝压缩链表到新节点
* Copy original ziplist so we can split it
*/
memcpy(new_node->zl, node->zl, zl_sz);
/* -1 here means "continue deleting until the list ends" */
int orig_start = after ? offset + 1 : 0;
int orig_extent = after ? -1 : offset;
int new_start = after ? 0 : offset;
int new_extent = after ? offset + 1 : -1;
D("After %d (%d); ranges: [%d, %d], [%d, %d]", after, offset, orig_start,
orig_extent, new_start, new_extent);
//删除orig_start到orig_extent的压缩链表节点项
node->zl = ziplistDeleteRange(node->zl, orig_start, orig_extent);
node->count = ziplistLen(node->zl);
quicklistNodeUpdateSz(node);
//删除new_start到new_extent的压缩链表节点项
new_node->zl = ziplistDeleteRange(new_node->zl, new_start, new_extent);
new_node->count = ziplistLen(new_node->zl);
quicklistNodeUpdateSz(new_node);
D("After split lengths: orig (%d), new (%d)", node->count, new_node->count);
return new_node;
}
/* 根据after的值在快速链表项前/后插入新项，值为value,大小为sz
* Insert a new entry before or after existing entry 'entry'.
*
* If after == 1, the new value is inserted after 'entry', otherwise
* the new value is inserted before 'entry'.
*/
REDIS_STATIC void _quicklistInsert(quicklist *quicklist, quicklistEntry *entry,
void *value, const size_t sz, int after) {
int full = 0, at_tail = 0, at_head = 0, full_next = 0, full_prev = 0;
int fill = quicklist->fill;
quicklistNode *node = entry->node;
quicklistNode *new_node = NULL;
//若该快速链表为空则很简单，直接插入即可
if (!node) {
/* we have no reference node, so let's create only node in the list */
D("No node given!");
new_node = quicklistCreateNode();
new_node->zl = ziplistPush(ziplistNew(), value, sz, ZIPLIST_HEAD);
__quicklistInsertNode(quicklist, NULL, new_node, after);
new_node->count++;
quicklist->count++;
return;
}
/* 检测当前节点是否可以插入
* Populate accounting flags for easier boolean checks later
*/
if (!_quicklistNodeAllowInsert(node, fill, sz)) {
D("Current node is full with count %d with requested fill %lu",
node->count, fill);
full = 1;
}
//尾部插入的情况，检测是否可以插入
if (after && (entry->offset == node->count)) {
D("At Tail of current ziplist");
at_tail = 1;
if (!_quicklistNodeAllowInsert(node->next, fill, sz)) {
D("Next node is full too.");
full_next = 1;
}
}
//头部插入的情况，检测是否可以插入
if (!after && (entry->offset == 0)) {
D("At Head");
at_head = 1;
if (!_quicklistNodeAllowInsert(node->prev, fill, sz)) {
D("Prev node is full too.");
full_prev = 1;
}
}
/* 根据上面的检测决定如何、在哪里插入新元素
* Now determine where and how to insert the new element
*/
if (!full && after) {
D("Not full, inserting after current position.");
quicklistDecompressNodeForUse(node);
unsigned char *next = ziplistNext(node->zl, entry->zi);
if (next == NULL) {
node->zl = ziplistPush(node->zl, value, sz, ZIPLIST_TAIL);
} else {
node->zl = ziplistInsert(node->zl, next, value, sz);
}
node->count++;
quicklistNodeUpdateSz(node);
quicklistRecompressOnly(quicklist, node);
} else if (!full && !after) {
D("Not full, inserting before current position.");
quicklistDecompressNodeForUse(node);
node->zl = ziplistInsert(node->zl, entry->zi, value, sz);
node->count++;
quicklistNodeUpdateSz(node);
quicklistRecompressOnly(quicklist, node);
} else if (full && at_tail && node->next && !full_next && after) {
/* If we are: at tail, next has free space, and inserting after:
* - insert entry at head of next node. */
D("Full and tail, but next isn't full; inserting next node head");
new_node = node->next;
quicklistDecompressNodeForUse(new_node);
new_node->zl = ziplistPush(new_node->zl, value, sz, ZIPLIST_HEAD);
new_node->count++;
quicklistNodeUpdateSz(new_node);
quicklistRecompressOnly(quicklist, new_node);
} else if (full && at_head && node->prev && !full_prev && !after) {
/* If we are: at head, previous has free space, and inserting before:
* - insert entry at tail of previous node. */
D("Full and head, but prev isn't full, inserting prev node tail");
new_node = node->prev;
quicklistDecompressNodeForUse(new_node);
new_node->zl = ziplistPush(new_node->zl, value, sz, ZIPLIST_TAIL);
new_node->count++;
quicklistNodeUpdateSz(new_node);
quicklistRecompressOnly(quicklist, new_node);
} else if (full && ((at_tail && node->next && full_next && after) ||
(at_head && node->prev && full_prev && !after))) {
/* If we are: full, and our prev/next is full, then:
* - create new node and attach to quicklist */
D("\tprovisioning new node...");
new_node = quicklistCreateNode();
new_node->zl = ziplistPush(ziplistNew(), value, sz, ZIPLIST_HEAD);
new_node->count++;
quicklistNodeUpdateSz(new_node);
__quicklistInsertNode(quicklist, node, new_node, after);
} else if (full) {
/* else, node is full we need to split it. */
/* covers both after and !after cases */
D("\tsplitting node...");
quicklistDecompressNodeForUse(node);
new_node = _quicklistSplitNode(node, entry->offset, after);
new_node->zl = ziplistPush(new_node->zl, value, sz,
after ? ZIPLIST_HEAD : ZIPLIST_TAIL);
new_node->count++;
quicklistNodeUpdateSz(new_node);
__quicklistInsertNode(quicklist, node, new_node, after);
_quicklistMergeNodes(quicklist, node);
}
quicklist->count++;
}
void quicklistInsertBefore(quicklist *quicklist, quicklistEntry *entry,
void *value, const size_t sz) {
_quicklistInsert(quicklist, entry, value, sz, 0);
}
void quicklistInsertAfter(quicklist *quicklist, quicklistEntry *entry,
void *value, const size_t sz) {
_quicklistInsert(quicklist, entry, value, sz, 1);
}
/* 删除一个范围内的快速链表
* Delete a range of elements from the quicklist.
*
* elements may span across multiple quicklistNodes, so we
* have to be careful about tracking where we start and end.
*
* Returns 1 if entries were deleted, 0 if nothing was deleted.
*/
int quicklistDelRange(quicklist *quicklist, const long start,
const long count) {
if (count <= 0)
return 0;
unsigned long extent = count; /* range is inclusive of start position */
//考虑到可能范围超过了存在的节点数，因此需要对start和count进行判断处理
if (start >= 0 && extent > (quicklist->count - start)) {
/* if requesting delete more elements than exist, limit to list size. */
extent = quicklist->count - start;
} else if (start < 0 && extent > (unsigned long)(-start)) {
/* else, if at negative offset, limit max size to rest of list. */
extent = -start; /* c.f. LREM -29 29; just delete until end. */
}
//根据start查找入口节点entry
quicklistEntry entry;
if (!quicklistIndex(quicklist, start, &entry))
return 0;
D("Quicklist delete request for start %ld, count %ld, extent: %ld", start,
count, extent);
quicklistNode *node = entry.node;
/* 循环删除所有节点
* iterate over next nodes until everything is deleted.
*/
while (extent) {
quicklistNode *next = node->next;
unsigned long del;
int delete_entire_node = 0;
if (entry.offset == 0 && extent >= node->count) {
/* 若需要删除的多于节点总数，则直接删除整个节点
* If we are deleting more than the count of this node, we
* can just delete the entire node without ziplist math.
*/
delete_entire_node = 1;
del = node->count;
} else if (entry.offset >= 0 && extent >= node->count) {
/* 根据需要删除节点数计算删除数
* If deleting more nodes after this one, calculate delete based
* on size of current node.
*/
del = node->count - entry.offset;
} else if (entry.offset < 0) {
/* 负值表示删除整个范围
* If offset is negative, we are in the first run of this loop
* and we are deleting the entire range
* from this start offset to end of list. Since the Negative
* offset is the number of elements until the tail of the list,
* just use it directly as the deletion count.
*/
del = -entry.offset;
/* If the positive offset is greater than the remaining extent,
* we only delete the remaining extent, not the entire offset.
*/
if (del > extent)
del = extent;
} else {
/* else, we are deleting less than the extent of this node, so
* use extent directly. */
del = extent;
}
D("[%ld]: asking to del: %ld because offset: %d; (ENTIRE NODE: %d), "
"node count: %u",
extent, del, entry.offset, delete_entire_node, node->count);
if (delete_entire_node) {
__quicklistDelNode(quicklist, node);
} else {
quicklistDecompressNodeForUse(node);
node->zl = ziplistDeleteRange(node->zl, entry.offset, del);
quicklistNodeUpdateSz(node);
node->count -= del;
quicklist->count -= del;
quicklistDeleteIfEmpty(quicklist, node);
if (node)
quicklistRecompressOnly(quicklist, node);
}
extent -= del;
node = next;
entry.offset = 0;
}
return 1;
}
/* Passthrough to ziplistCompare() */
int quicklistCompare(unsigned char *p1, unsigned char *p2, int p2_len) {
return ziplistCompare(p1, p2, p2_len);
}
/* 返回快速列表迭代器
* 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;
iter = zmalloc(sizeof(*iter));
//根据方向赋值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;
}
/* 在指定位置idx初始化一个iter迭代器指针
* 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;
//原理就是先找到指定节点，再在指定节点获取iter，再给其赋值
if (quicklistIndex(quicklist, idx, &entry)) {
quicklistIter *base = quicklistGetIterator(quicklist, direction);
base->zi = NULL;
base->current = entry.node;
base->offset = entry.offset;
return base;
} else {
return NULL;
}
}
/* Release iterator.
* If we still have a valid current node, then re-encode current node. */
void quicklistReleaseIterator(quicklistIter *iter) {
if (iter->current)
quicklistCompress(iter->quicklist, iter->current);
zfree(iter);
}
/* 获取下一个iter
* 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);
//空指针异常处理
if (!iter) {
D("Returning because no iter!");
return 0;
}
//记录当前iter
entry->quicklist = iter->quicklist;
entry->node = iter->current;
//节点空则返回
if (!iter->current) {
D("Returning because current node is NULL")
return 0;
}
//函数指针用于根据方向判断调用上一个还是下一个的函数
unsigned char *(*nextFn)(unsigned char *, unsigned char *) = NULL;
int offset_update = 0;
//若zi为空则获取当前索引
if (!iter->zi) {
/* If !zi, use current index. */
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;
}
iter->zi = nextFn(iter->current->zl, iter->zi);
iter->offset += offset_update;
}
//记录zi和offset
entry->zi = iter->zi;
entry->offset = iter->offset;
//若zi大于0则直接获取并返回，否则需要进入下一个快速链表项
if (iter->zi) {
/* Populate value from existing ziplist position */
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. */
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);
}
}
/* 复制快速链表，返回复制成功的原快速链表
* Duplicate the quicklist.
* On success a copy of the original quicklist is returned.
*
* The original quicklist both on success or error is never modified.
*
* Returns newly allocated quicklist.
*/
quicklist *quicklistDup(quicklist *orig) {
quicklist *copy;
//创建新的链表
copy = quicklistNew(orig->fill, orig->compress);
//循环获取每一个快速链表节点并拷贝
for (quicklistNode *current = orig->head; current;
current = current->next) {
quicklistNode *node = quicklistCreateNode();
//根据编码类型不同进行不同赋值
if (current->encoding == QUICKLIST_NODE_ENCODING_LZF) {
quicklistLZF *lzf = (quicklistLZF *)current->zl;
size_t lzf_sz = sizeof(*lzf) + lzf->sz;
node->zl = zmalloc(lzf_sz);
memcpy(node->zl, current->zl, lzf_sz);
} else if (current->encoding == QUICKLIST_NODE_ENCODING_RAW) {
node->zl = zmalloc(current->sz);
memcpy(node->zl, current->zl, current->sz);
}
node->count = current->count;
copy->count += node->count;
node->sz = current->sz;
node->encoding = current->encoding;
//在拷贝快速链表中插入该项
_quicklistInsertNodeAfter(copy, copy->tail, node);
}
/* copy->count must equal orig->count here */
return copy;
}
/* 根据idx返回对应的快速链表项
* 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 */
initEntry(entry);
entry->quicklist = quicklist;
//根据forward判断方向
if (!forward) {
index = (-idx) - 1;
n = quicklist->tail;
} else {
index = idx;
n = quicklist->head;
}
if (index >= quicklist->count)
return 0;
//查找节点
while (likely(n)) {
if ((accum + n->count) > index) {
break;
} else {
D("Skipping over (%p) %u at accum %lld", (void *)n, n->count,
accum);
accum += n->count;
n = forward ? n->next : n->prev;
}
}
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);
//根据找到的节点赋值
entry->node = n;
if (forward) {
/* forward = normal head-to-tail offset. */
entry->offset = index - accum;
} else {
/* reverse = need negative offset for tail-to-head, so undo
* the result of the original if (index < 0) above. */
entry->offset = (-index) - 1 + accum;
}
//解压节点并赋值
quicklistDecompressNodeForUse(entry->node);
entry->zi = ziplistIndex(entry->node->zl, entry->offset);
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;
}
/* 旋转快速链表：首尾位置互换
* Rotate quicklist by moving the tail element to the head.
*/
void quicklistRotate(quicklist *quicklist) {
if (quicklist->count <= 1)
return;
/* 获取尾部节点
* First, get the tail entry
*/
unsigned char *p = ziplistIndex(quicklist->tail->zl, -1);
unsigned char *value;
long long longval;
unsigned int sz;
char longstr[32] = {0};
ziplistGet(p, &value, &sz, &longval);
/* 若尾节点值为空则赋值0
* If value found is NULL, then ziplistGet populated longval instead
*/
if (!value) {
/* Write the longval as a string so we can re-add it */
sz = ll2string(longstr, sizeof(longstr), longval);
value = (unsigned char *)longstr;
}
/* 将尾部节点加入头部
* Add tail entry to head (must happen before tail is deleted).
*/
quicklistPushHead(quicklist, value, sz);
/* 针对仅有一个节点的特殊处理：重新获取p
* If quicklist has only one node, the head ziplist is also the
* tail ziplist and PushHead() could have reallocated our single ziplist,
* which would make our pre-existing 'p' unusable.
*/
if (quicklist->len == 1) {
p = ziplistIndex(quicklist->tail->zl, -1);
}
/* Remove tail entry. */
quicklistDelIndex(quicklist, quicklist->tail, &p);
}
/* 从快速链表弹出一项，返回数据指针。where必须为首或者尾部，不能弹出中间项
* 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;
//判断首尾
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 = 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;
}
quicklistDelIndex(quicklist, node, &p);
return 1;
}
return 0;
}
/* Return a malloc'd copy of data passed in */
REDIS_STATIC void *_quicklistSaver(unsigned char *data, unsigned int sz) {
unsigned char *vstr;
if (data) {
vstr = zmalloc(sz);
memcpy(vstr, data, sz);
return vstr;
}
return NULL;
}
/* 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;
int ret = quicklistPopCustom(quicklist, where, &vstr, &vlen, &vlong,
_quicklistSaver);
if (data)
*data = vstr;
if (slong)
*slong = vlong;
if (sz)
*sz = vlen;
return ret;
}
/* 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) {
quicklistPushHead(quicklist, value, sz);
} else if (where == QUICKLIST_TAIL) {
quicklistPushTail(quicklist, value, sz);
}
}
标签：node,quicklist,iter,next,链表,源码,offset,entry,解析 来源： https://blog.csdn.net/u013354486/article/details/100824617