raxNewNode() 用于新建一个没有压缩的节点，如果 datafield 为真，则 data[] 将多申请一个指针的空间容纳指向卫星数据的指针。
/* Allocate a new non compressed node with the specified number of children.
* If datafiled is true, the allocation is made large enough to hold the
* associated data pointer.
* Returns the new node pointer. On out of memory NULL is returned. */
raxNode *raxNewNode(size_t children, int datafield) {
size_t nodesize = sizeof(raxNode)+children+
sizeof(raxNode*)*children;
if (datafield) nodesize += sizeof(void*);
raxNode *node = rax_malloc(nodesize);
if (node == NULL) return NULL;
node->iskey = 0;
node->isnull = 0;
node->iscompr = 0;
node->size = children;
return node;
}
raxNew() 用于新建一个基数树:
/* Allocate a new rax and return its pointer. On out of memory the function
* returns NULL. */
rax *raxNew(void) {
rax *rax = rax_malloc(sizeof(*rax));
if (rax == NULL) return NULL;
rax->numele = 0;
rax->numnodes = 1;
rax->head = raxNewNode(0,0);
if (rax->head == NULL) {
rax_free(rax);
return NULL;
} else {
return rax;
}
}
一个节点占用多少空间是很繁琐的一个计算，redis 用一个宏 raxNodeCurrentLength 来完成这个计算：
/* Return the current total size of the node. */
#define raxNodeCurrentLength(n) ( \
sizeof(raxNode)+(n)->size+ \
((n)->iscompr ? sizeof(raxNode*) : sizeof(raxNode*)*(n)->size)+ \
(((n)->iskey && !(n)->isnull)*sizeof(void*)) \
)
raxReallocForData() 用于扩充一个节点的空间以容纳一个指针：
/* realloc the node to make room for auxiliary data in order
* to store an item in that node. On out of memory NULL is returned. */
raxNode *raxReallocForData(raxNode *n, void *data) {
if (data == NULL) return n; /* No reallocation needed, setting isnull=1 */
size_t curlen = raxNodeCurrentLength(n);
return rax_realloc(n,curlen+sizeof(void*));
}
raxSetData() 用于将数据指针存放到节点上：
/* Set the node auxiliary data to the specified pointer. */
void raxSetData(raxNode *n, void *data) {
n->iskey = 1;
if (data != NULL) {
void **ndata = (void**)
((char*)n+raxNodeCurrentLength(n)-sizeof(void*));
memcpy(ndata,&data,sizeof(data));
n->isnull = 0;
} else {
n->isnull = 1;
}
}
raxGetData() 用于从节点获得数据指针：
/* Get the node auxiliary data. */
void *raxGetData(raxNode *n) {
if (n->isnull) return NULL;
void **ndata =(void**)((char*)n+raxNodeCurrentLength(n)-sizeof(void*));
void *data;
memcpy(&data,ndata,sizeof(data));
return data;
}
raxNode *raxAddChild(raxNode *n, unsigned char c, raxNode**childptr,raxNode ***parentlink) 向一个节点 n 插入一个表示字符 c 的子节点，并返回 n 的新地址。 parentlink 指向父节点 n 中指向新子节点的指针， childptr 存储新子节点的 地址。新的父节点的空间将是旧空间加上一个容纳字符的字节以及一个容纳指针 的空间。注意压缩节点是不能插入子节点的，必须分裂或才能插入。
/* Add a new child to the node 'n' representing the character 'c' and return
* its new pointer, as well as the child pointer by reference. Additionally
* '***parentlink' is populated with the raxNode pointer-to-pointer of where
* the new child was stored, which is useful for the caller to replace the
* child pointer if it gets reallocated.
*
* On success the new parent node pointer is returned (it may change because
* of the realloc, so the caller should discard 'n' and use the new value).
* On out of memory NULL is returned, and the old node is still valid. */
raxNode *raxAddChild(raxNode *n, unsigned char c, raxNode **childptr, raxNode ***parentlink) {
assert(n->iscompr == 0);
size_t curlen = sizeof(raxNode)+
n->size+
sizeof(raxNode*)*n->size;
size_t newlen;
/* Alloc the new child we will link to 'n'. */
raxNode *child = raxNewNode(0,0);
if (child == NULL) return NULL;
/* Make space in the original node. */
if (n->iskey) curlen += sizeof(void*);
newlen = curlen+sizeof(raxNode*)+1; /* Add 1 char and 1 pointer. */
raxNode *newn = rax_realloc(n,newlen);
if (newn == NULL) {
rax_free(child);
return NULL;
}
n = newn;
/* After the reallocation, we have 5/9 (depending on the system
* pointer size) bytes at the end, that is, the additional char
* in the 'data' section, plus one pointer to the new child:
*
* [numc][abx][ap][bp][xp]|auxp|.....
*
* Let's find where to insert the new child in order to make sure
* it is inserted in-place lexicographically. */
int pos;
for (pos = 0; pos < n->size; pos++) {
if (n->data[pos] > c) break;
}
/* Now, if present, move auxiliary data pointer at the end
* so that we can mess with the other data without overwriting it.
* We will obtain something like that:
*
* [numc][abx][ap][bp][xp].....|auxp| */
unsigned char *src;
if (n->iskey && !n->isnull) {
src = n->data+n->size+sizeof(raxNode*)*n->size;
memmove(src+1+sizeof(raxNode*),src,sizeof(void*));
}
/* Now imagine we are adding a node with edge 'c'. The insertion
* point is between 'b' and 'x', so the 'pos' variable value is
* To start, move all the child pointers after the insertion point
* of 1+sizeof(pointer) bytes on the right, to obtain:
*
* [numc][abx][ap][bp].....[xp]|auxp| */
src = n->data+n->size+sizeof(raxNode*)*pos;
memmove(src+1+sizeof(raxNode*),src,sizeof(raxNode*)*(n->size-pos));
/* Now make the space for the additional char in the data section,
* but also move the pointers before the insertion point in the right
* by 1 byte, in order to obtain the following:
*
* [numc][ab.x][ap][bp]....[xp]|auxp| */
src = n->data+pos;
memmove(src+1,src,n->size-pos+sizeof(raxNode*)*pos);
/* We can now set the character and its child node pointer to get:
*
* [numc][abcx][ap][bp][cp]....|auxp|
* [numc][abcx][ap][bp][cp][xp]|auxp| */
n->data[pos] = c;
n->size++;
raxNode **childfield = (raxNode**)(n->data+n->size+sizeof(raxNode*)*pos);
memcpy(childfield,&child,sizeof(child));
*childptr = child;
*parentlink = childfield;
return n;
}
raxNodeLastChildPtr 可以获得一个节点的最后一个子节点，如果节点是压缩的， 就返回唯一的节点。
/* Return the pointer to the last child pointer in a node. For the compressed
* nodes this is the only child pointer. */
#define raxNodeLastChildPtr(n) ((raxNode**) ( \
((char*)(n)) + \
raxNodeCurrentLength(n) - \
sizeof(raxNode*) - \
(((n)->iskey && !(n)->isnull) ? sizeof(void*) : 0) \
))
raxNodeFirstChildPtr 则返回第一个子节点：
/* Return the pointer to the first child pointer. */
#define raxNodeFirstChildPtr(n) ((raxNode**)((n)->data+(n)->size))
raxCompressNode() 用于压缩一个节点， n 必须没有子节点，新节点的空间需 要容纳所有字符，以及一个子节点的指针。
/* Turn the node 'n', that must be a node without any children, into a
* compressed node representing a set of nodes linked one after the other
* and having exactly one child each. The node can be a key or not: this
* property and the associated value if any will be preserved.
*
* The function also returns a child node, since the last node of the
* compressed chain cannot be part of the chain: it has zero children while
* we can only compress inner nodes with exactly one child each. */
raxNode *raxCompressNode(raxNode *n, unsigned char *s, size_t len, raxNode **child) {
assert(n->size == 0 && n->iscompr == 0);
void *data = NULL; /* Initialized only to avoid warnings. */
size_t newsize;
debugf("Compress node: %.*s\n", (int)len,s);
/* Allocate the child to link to this node. */
*child = raxNewNode(0,0);
if (*child == NULL) return NULL;
/* Make space in the parent node. */
newsize = sizeof(raxNode)+len+sizeof(raxNode*);
if (n->iskey) {
data = raxGetData(n); /* To restore it later. */
if (!n->isnull) newsize += sizeof(void*);
}
raxNode *newn = rax_realloc(n,newsize);
if (newn == NULL) {
rax_free(*child);
return NULL;
}
n = newn;
n->iscompr = 1;
n->size = len;
memcpy(n->data,s,len);
if (n->iskey) raxSetData(n,data);
raxNode **childfield = raxNodeLastChildPtr(n);
memcpy(childfield,child,sizeof(*child));
return n;
}
raxLowWalk() 在基数树中查找字符串 s 的位置，返回值是匹配过的字符数， stopnode 是查找结束的位置， plink 是父节点，如果最后在压缩节点中停止， 则 splitpos 记录节点中需要分裂的位置， ts 是一个栈，保存从根节点到停止 节点经过的所有节点。
static inline size_t raxLowWalk(rax *rax, unsigned char *s, size_t len, raxNode **stopnode, raxNode ***plink, int *splitpos, raxStack *ts) {
raxNode *h = rax->head;
raxNode **parentlink = &rax->head;
size_t i = 0; /* Position in the string. */
size_t j = 0; /* Position in the node children (or bytes if compressed).*/
while(h->size && i < len) {
debugnode("Lookup current node",h);
unsigned char *v = h->data;
if (h->iscompr) {
for (j = 0; j < h->size && i < len; j++, i++) {
if (v[j] != s[i]) break;
}
if (j != h->size) break;
} else {
/* Even when h->size is large, linear scan provides good
* performances compared to other approaches that are in theory
* more sounding, like performing a binary search. */
for (j = 0; j < h->size; j++) {
if (v[j] == s[i]) break;
}
if (j == h->size) break;
i++;
}
if (ts) raxStackPush(ts,h); /* Save stack of parent nodes. */
raxNode **children = raxNodeFirstChildPtr(h);
if (h->iscompr) j = 0; /* Compressed node only child is at index 0. */
memcpy(&h,children+j,sizeof(h));
parentlink = children+j;
j = 0; /* If the new node is compressed and we do not
iterate again (since i == l) set the split
position to 0 to signal this node represents
the searched key. */
}
if (stopnode) *stopnode = h;
if (plink) *plink = parentlink;
if (splitpos && h->iscompr) *splitpos = j;
return i;
}
raxInsert() 负责插入一个元素，期间包括节点分裂的过程，比较复杂。首先调 用 raxLowWalk() 确定插入位置。如果已经匹配的字符串长度等于要插入的字符 串 s 的长度，并且停止节点不是压缩节点，那么要么字符串已经在基数树中， 要么基数树里的节点足以表示这个字符串，只要调整节点修改相关字段即可。
如果 raxLowWalk() 在压缩节点停止，就要分裂这个节点以继续插入过程。节点分裂有 5 种情 况，下面以一个基数树举例：
"ANNIBALE" -> "SCO" -> []
1) Inserting "ANNIENTARE"
|B| -> "ALE" -> "SCO" -> []
"ANNI" -> |-|
|E| -> (... continue algo ...) "NTARE" -> []
2) Inserting "ANNIBALI"
|E| -> "SCO" -> []
"ANNIBAL" -> |-|
|I| -> (... continue algo ...) []
3) Inserting "AGO" (Like case 1, but set iscompr = 0 into original node)
|N| -> "NIBALE" -> "SCO" -> []
|A| -> |-|
|G| -> (... continue algo ...) |O| -> []
4) Inserting "CIAO"
|A| -> "NNIBALE" -> "SCO" -> []
|-|
|C| -> (... continue algo ...) "IAO" -> []
5) Inserting "ANNI"
"ANNI" -> "BALE" -> "SCO" -> []
需要两个算法完成分裂操作：
算法1
当不是第 5 种情况时：
- 保存当前压缩节点的
$NEXT指针，也就是指向这个节点唯一子节点的指针。 - 创建分裂节点。
3a. 如果 $SPLITPOS 为 0，则将用户数据复制到分裂节点上。 3b. 如果 $SPLITPOS 不为 0，减少这个节点的空间，因为只需要容纳 $splitpos 个字符。 4a. 如果分裂后剩余的字符长度不为 0，创建 postfix 节点，并将 子节点指针指向 $NEXT 。 4b. 如果 postfix 节点长度为 0，则直接使用 $NEXT 节点作为
postfix 节点。
- 设置分裂节点的
child[0]为 postfix 节点。 - 进入分裂节点，继续插入过程。
算法2
第 5 种情况种，如果在压缩节点停下但并不是不匹配，那么
- 保存
$NEXT。 - 创建 postfix 节点，容纳
$SPLITPOS到结束的所有字符。 - 整理当前结点的内存空间，如果有用户数据，则设置。
- postfix 是当前节点的唯一子节点。
分裂之后，可能需要继续插入一个节点，以容纳没有匹配的字符：
/* Insert the element 's' of size 'len', setting as auxiliary data
* the pointer 'data'. If the element is already present, the associated
* data is updated, and 0 is returned, otherwise the element is inserted
* and 1 is returned. On out of memory the function returns 0 as well but
* sets errno to ENOMEM, otherwise errno will be set to 0. */
int raxInsert(rax *rax, unsigned char *s, size_t len, void *data, void **old) {
size_t i;
int j = 0; /* Split position. If raxLowWalk() stops in a compressed
node, the index 'j' represents the char we stopped within the
compressed node, that is, the position where to split the
node for insertion. */
raxNode *h, **parentlink;
debugf("### Insert %.*s with value %p\n", (int)len, s, data);
i = raxLowWalk(rax,s,len,&h,&parentlink,&j,NULL);
/* If i == len we walked following the whole string. If we are not
* in the middle of a compressed node, the string is either already
* inserted or this middle node is currently not a key, but can represent
* our key. We have just to reallocate the node and make space for the
* data pointer. */
if (i == len && (!h->iscompr || j == 0 /* not in the middle if j is 0 */)) {
if (h->iskey) {
if (old) *old = raxGetData(h);
raxSetData(h,data);
errno = 0;
return 0; /* Element already exists. */
}
h = raxReallocForData(h,data);
if (h == NULL) {
errno = ENOMEM;
return 0;
}
memcpy(parentlink,&h,sizeof(h));
raxSetData(h,data);
rax->numele++;
return 1; /* Element inserted. */
}
/* ------------------------- ALGORITHM 1 --------------------------- */
if (h->iscompr && i != len) {
debugf("ALGO 1: Stopped at compressed node %.*s (%p)\n",
h->size, h->data, (void*)h);
debugf("Still to insert: %.*s\n", (int)(len-i), s+i);
debugf("Splitting at %d: '%c'\n", j, ((char*)h->data)[j]);
debugf("Other (key) letter is '%c'\n", s[i]);
/* 1: Save next pointer. */
raxNode **childfield = raxNodeLastChildPtr(h);
raxNode *next;
memcpy(&next,childfield,sizeof(next));
debugf("Next is %p\n", (void*)next);
debugf("iskey %d\n", h->iskey);
if (h->iskey) {
debugf("key value is %p\n", raxGetData(h));
}
/* Set the length of the additional nodes we will need. */
size_t trimmedlen = j;
size_t postfixlen = h->size - j - 1;
int split_node_is_key = !trimmedlen && h->iskey && !h->isnull;
size_t nodesize;
/* 2: Create the split node. Also allocate the other nodes we'll need
* ASAP, so that it will be simpler to handle OOM. */
raxNode *splitnode = raxNewNode(1, split_node_is_key);
raxNode *trimmed = NULL;
raxNode *postfix = NULL;
if (trimmedlen) {
nodesize = sizeof(raxNode)+trimmedlen+sizeof(raxNode*);
if (h->iskey && !h->isnull) nodesize += sizeof(void*);
trimmed = rax_malloc(nodesize);
}
if (postfixlen) {
nodesize = sizeof(raxNode)+postfixlen+
sizeof(raxNode*);
postfix = rax_malloc(nodesize);
}
/* OOM? Abort now that the tree is untouched. */
if (splitnode == NULL ||
(trimmedlen && trimmed == NULL) ||
(postfixlen && postfix == NULL))
{
rax_free(splitnode);
rax_free(trimmed);
rax_free(postfix);
errno = ENOMEM;
return 0;
}
splitnode->data[0] = h->data[j];
if (j == 0) {
/* 3a: Replace the old node with the split node. */
if (h->iskey) {
void *ndata = raxGetData(h);
raxSetData(splitnode,ndata);
}
memcpy(parentlink,&splitnode,sizeof(splitnode));
} else {
/* 3b: Trim the compressed node. */
trimmed->size = j;
memcpy(trimmed->data,h->data,j);
trimmed->iscompr = j > 1 ? 1 : 0;
trimmed->iskey = h->iskey;
trimmed->isnull = h->isnull;
if (h->iskey && !h->isnull) {
void *ndata = raxGetData(h);
raxSetData(trimmed,ndata);
}
raxNode **cp = raxNodeLastChildPtr(trimmed);
memcpy(cp,&splitnode,sizeof(splitnode));
memcpy(parentlink,&trimmed,sizeof(trimmed));
parentlink = cp; /* Set parentlink to splitnode parent. */
rax->numnodes++;
}
/* 4: Create the postfix node: what remains of the original
* compressed node after the split. */
if (postfixlen) {
/* 4a: create a postfix node. */
postfix->iskey = 0;
postfix->isnull = 0;
postfix->size = postfixlen;
postfix->iscompr = postfixlen > 1;
memcpy(postfix->data,h->data+j+1,postfixlen);
raxNode **cp = raxNodeLastChildPtr(postfix);
memcpy(cp,&next,sizeof(next));
rax->numnodes++;
} else {
/* 4b: just use next as postfix node. */
postfix = next;
}
/* 5: Set splitnode first child as the postfix node. */
raxNode **splitchild = raxNodeLastChildPtr(splitnode);
memcpy(splitchild,&postfix,sizeof(postfix));
/* 6. Continue insertion: this will cause the splitnode to
* get a new child (the non common character at the currently
* inserted key). */
rax_free(h);
h = splitnode;
} else if (h->iscompr && i == len) {
/* ------------------------- ALGORITHM 2 --------------------------- */
debugf("ALGO 2: Stopped at compressed node %.*s (%p) j = %d\n",
h->size, h->data, (void*)h, j);
/* Allocate postfix & trimmed nodes ASAP to fail for OOM gracefully. */
size_t postfixlen = h->size - j;
size_t nodesize = sizeof(raxNode)+postfixlen+sizeof(raxNode*);
if (data != NULL) nodesize += sizeof(void*);
raxNode *postfix = rax_malloc(nodesize);
nodesize = sizeof(raxNode)+j+sizeof(raxNode*);
if (h->iskey && !h->isnull) nodesize += sizeof(void*);
raxNode *trimmed = rax_malloc(nodesize);
if (postfix == NULL || trimmed == NULL) {
rax_free(postfix);
rax_free(trimmed);
errno = ENOMEM;
return 0;
}
/* 1: Save next pointer. */
raxNode **childfield = raxNodeLastChildPtr(h);
raxNode *next;
memcpy(&next,childfield,sizeof(next));
/* 2: Create the postfix node. */
postfix->size = postfixlen;
postfix->iscompr = postfixlen > 1;
postfix->iskey = 1;
postfix->isnull = 0;
memcpy(postfix->data,h->data+j,postfixlen);
raxSetData(postfix,data);
raxNode **cp = raxNodeLastChildPtr(postfix);
memcpy(cp,&next,sizeof(next));
rax->numnodes++;
/* 3: Trim the compressed node. */
trimmed->size = j;
trimmed->iscompr = j > 1;
trimmed->iskey = 0;
trimmed->isnull = 0;
memcpy(trimmed->data,h->data,j);
memcpy(parentlink,&trimmed,sizeof(trimmed));
if (h->iskey) {
void *aux = raxGetData(h);
raxSetData(trimmed,aux);
}
/* Fix the trimmed node child pointer to point to
* the postfix node. */
cp = raxNodeLastChildPtr(trimmed);
memcpy(cp,&postfix,sizeof(postfix));
/* Finish! We don't need to contine with the insertion
* algorithm for ALGO 2. The key is already inserted. */
rax->numele++;
rax_free(h);
return 1; /* Key inserted. */
}
/* We walked the radix tree as far as we could, but still there are left
* chars in our string. We need to insert the missing nodes.
* Note: while loop never entered if the node was split by ALGO2,
* since i == len. */
while(i < len) {
raxNode *child;
/* If this node is going to have a single child, and there
* are other characters, so that that would result in a chain
* of single-childed nodes, turn it into a compressed node. */
if (h->size == 0 && len-i > 1) {
debugf("Inserting compressed node\n");
size_t comprsize = len-i;
if (comprsize > RAX_NODE_MAX_SIZE)
comprsize = RAX_NODE_MAX_SIZE;
raxNode *newh = raxCompressNode(h,s+i,comprsize,&child);
if (newh == NULL) goto oom;
h = newh;
memcpy(parentlink,&h,sizeof(h));
parentlink = raxNodeLastChildPtr(h);
i += comprsize;
} else {
debugf("Inserting normal node\n");
raxNode **new_parentlink;
raxNode *newh = raxAddChild(h,s[i],&child,&new_parentlink);
if (newh == NULL) goto oom;
h = newh;
memcpy(parentlink,&h,sizeof(h));
parentlink = new_parentlink;
i++;
}
rax->numnodes++;
h = child;
}
raxNode *newh = raxReallocForData(h,data);
if (newh == NULL) goto oom;
h = newh;
if (!h->iskey) rax->numele++;
raxSetData(h,data);
memcpy(parentlink,&h,sizeof(h));
return 1; /* Element inserted. */
oom:
/* This code path handles out of memory after part of the sub-tree was
* already modified. Set the node as a key, and then remove it. However we
* do that only if the node is a terminal node, otherwise if the OOM
* happened reallocating a node in the middle, we don't need to free
* anything. */
if (h->size == 0) {
h->isnull = 1;
h->iskey = 1;
rax->numele++; /* Compensate the next remove. */
assert(raxRemove(rax,s,i,NULL) != 0);
}
errno = ENOMEM;
return 0;
}
raxFind() 查找某个 key ，并返回对应的用户数据指针。如果没有找到，则返 回 raxNotFound 。
/* Find a key in the rax, returns raxNotFound special void pointer value
* if the item was not found, otherwise the value associated with the
* item is returned. */
void *raxFind(rax *rax, unsigned char *s, size_t len) {
raxNode *h;
debugf("### Lookup: %.*s\n", (int)len, s);
int splitpos = 0;
size_t i = raxLowWalk(rax,s,len,&h,NULL,&splitpos,NULL);
if (i != len || (h->iscompr && splitpos != 0) || !h->iskey)
return raxNotFound;
return raxGetData(h);
}
raxFindParentLink 返回父节点中指向子节点的指针的地址:
/* Return the memory address where the 'parent' node stores the specified
* 'child' pointer, so that the caller can update the pointer with another
* one if needed. The function assumes it will find a match, otherwise the
* operation is an undefined behavior (it will continue scanning the
* memory without any bound checking). */
raxNode **raxFindParentLink(raxNode *parent, raxNode *child) {
raxNode **cp = raxNodeFirstChildPtr(parent);
raxNode *c;
while(1) {
memcpy(&c,cp,sizeof(c));
if (c == child) break;
cp++;
}
return cp;
}
raxRemoveChild() 从一个节点中删除一个子节点。如果父节点时压缩节点，只 需将父节点修改为没有子节点的普通空节点即可。否则就要查找要删除的子节点 的位置，再将其删除。
/* Low level child removal from node. The new node pointer (after the child
* removal) is returned. Note that this function does not fix the pointer
* of the parent node in its parent, so this task is up to the caller.
* The function never fails for out of memory. */
raxNode *raxRemoveChild(raxNode *parent, raxNode *child) {
debugnode("raxRemoveChild before", parent);
/* If parent is a compressed node (having a single child, as for definition
* of the data structure), the removal of the child consists into turning
* it into a normal node without children. */
if (parent->iscompr) {
void *data = NULL;
if (parent->iskey) data = raxGetData(parent);
parent->isnull = 0;
parent->iscompr = 0;
parent->size = 0;
if (parent->iskey) raxSetData(parent,data);
debugnode("raxRemoveChild after", parent);
return parent;
}
/* Otherwise we need to scan for the children pointer and memmove()
* accordingly.
*
* 1. To start we seek the first element in both the children
* pointers and edge bytes in the node. */
raxNode **cp = raxNodeFirstChildPtr(parent);
raxNode **c = cp;
unsigned char *e = parent->data;
/* 2. Search the child pointer to remove inside the array of children
* pointers. */
while(1) {
raxNode *aux;
memcpy(&aux,c,sizeof(aux));
if (aux == child) break;
c++;
e++;
}
/* 3. Remove the edge and the pointer by memmoving the remaining children
* pointer and edge bytes one position before. */
int taillen = parent->size - (e - parent->data) - 1;
debugf("raxRemoveChild tail len: %d\n", taillen);
memmove(e,e+1,taillen);
/* Since we have one data byte less, also child pointers start one byte
* before now. */
memmove(((char*)cp)-1,cp,(parent->size-taillen-1)*sizeof(raxNode**));
/* Move the remaining "tail" pointer at the right position as well. */
memmove(((char*)c)-1,c+1,taillen*sizeof(raxNode**)+parent->iskey*sizeof(void*));
/* 4. Update size. */
parent->size--;
/* realloc the node according to the theoretical memory usage, to free
* data if we are over-allocating right now. */
raxNode *newnode = rax_realloc(parent,raxNodeCurrentLength(parent));
if (newnode) {
debugnode("raxRemoveChild after", newnode);
}
/* Note: if rax_realloc() fails we just return the old address, which
* is valid. */
return newnode ? newnode : parent;
}
raxRemove() 将一个元素删除，如果发现并删除则返回 1， 否则返回 0。这个 操作可能需要合并节点。
首先同样需要 raxLowWalk() 找到一个代表要删除元素的节点，将其 iskey 字 段置 0。
如果这个节点没有子节点，那么上溯祖先节点逐个删除直到遇到一个有 两个以上子节点或者 iskey 为 1 的节点。
有两种情况需要用到压缩操作：
- 一个只有一个孩子的节点，并且这个节点
iskey为 0 。 - 原来有两个孩子的节点，现在只有一个了。
不断上溯直到没有需要压缩的节点为止，创建新节点，存储从这个节点开始需要 压缩的节点的数据。
/* Remove the specified item. Returns 1 if the item was found and
* deleted, 0 otherwise. */
int raxRemove(rax *rax, unsigned char *s, size_t len, void **old) {
raxNode *h;
raxStack ts;
debugf("### Delete: %.*s\n", (int)len, s);
raxStackInit(&ts);
int splitpos = 0;
size_t i = raxLowWalk(rax,s,len,&h,NULL,&splitpos,&ts);
if (i != len || (h->iscompr && splitpos != 0) || !h->iskey) {
raxStackFree(&ts);
return 0;
}
if (old) *old = raxGetData(h);
h->iskey = 0;
rax->numele--;
/* If this node has no children, the deletion needs to reclaim the
* no longer used nodes. This is an iterative process that needs to
* walk the three upward, deleting all the nodes with just one child
* that are not keys, until the head of the rax is reached or the first
* node with more than one child is found. */
int trycompress = 0; /* Will be set to 1 if we should try to optimize the
tree resulting from the deletion. */
if (h->size == 0) {
debugf("Key deleted in node without children. Cleanup needed.\n");
raxNode *child = NULL;
while(h != rax->head) {
child = h;
debugf("Freeing child %p [%.*s] key:%d\n", (void*)child,
(int)child->size, (char*)child->data, child->iskey);
rax_free(child);
rax->numnodes--;
h = raxStackPop(&ts);
/* If this node has more then one child, or actually holds
* a key, stop here. */
if (h->iskey || (!h->iscompr && h->size != 1)) break;
}
if (child) {
debugf("Unlinking child %p from parent %p\n",
(void*)child, (void*)h);
raxNode *new = raxRemoveChild(h,child);
if (new != h) {
raxNode *parent = raxStackPeek(&ts);
raxNode **parentlink;
if (parent == NULL) {
parentlink = &rax->head;
} else {
parentlink = raxFindParentLink(parent,h);
}
memcpy(parentlink,&new,sizeof(new));
}
/* If after the removal the node has just a single child
* and is not a key, we need to try to compress it. */
if (new->size == 1 && new->iskey == 0) {
trycompress = 1;
h = new;
}
}
} else if (h->size == 1) {
/* If the node had just one child, after the removal of the key
* further compression with adjacent nodes is pontentially possible. */
trycompress = 1;
}
/* Don't try node compression if our nodes pointers stack is not
* complete because of OOM while executing raxLowWalk() */
if (trycompress && ts.oom) trycompress = 0;
if (trycompress) {
debugf("After removing %.*s:\n", (int)len, s);
debugnode("Compression may be needed",h);
debugf("Seek start node\n");
/* Try to reach the upper node that is compressible.
* At the end of the loop 'h' will point to the first node we
* can try to compress and 'parent' to its parent. */
raxNode *parent;
while(1) {
parent = raxStackPop(&ts);
if (!parent || parent->iskey ||
(!parent->iscompr && parent->size != 1)) break;
h = parent;
debugnode("Going up to",h);
}
raxNode *start = h; /* Compression starting node. */
/* Scan chain of nodes we can compress. */
size_t comprsize = h->size;
int nodes = 1;
while(h->size != 0) {
raxNode **cp = raxNodeLastChildPtr(h);
memcpy(&h,cp,sizeof(h));
if (h->iskey || (!h->iscompr && h->size != 1)) break;
/* Stop here if going to the next node would result into
* a compressed node larger than h->size can hold. */
if (comprsize + h->size > RAX_NODE_MAX_SIZE) break;
nodes++;
comprsize += h->size;
}
if (nodes > 1) {
/* If we can compress, create the new node and populate it. */
size_t nodesize =
sizeof(raxNode)+comprsize+sizeof(raxNode*);
raxNode *new = rax_malloc(nodesize);
/* An out of memory here just means we cannot optimize this
* node, but the tree is left in a consistent state. */
if (new == NULL) {
raxStackFree(&ts);
return 1;
}
new->iskey = 0;
new->isnull = 0;
new->iscompr = 1;
new->size = comprsize;
rax->numnodes++;
/* Scan again, this time to populate the new node content and
* to fix the new node child pointer. At the same time we free
* all the nodes that we'll no longer use. */
comprsize = 0;
h = start;
while(h->size != 0) {
memcpy(new->data+comprsize,h->data,h->size);
comprsize += h->size;
raxNode **cp = raxNodeLastChildPtr(h);
raxNode *tofree = h;
memcpy(&h,cp,sizeof(h));
rax_free(tofree); rax->numnodes--;
if (h->iskey || (!h->iscompr && h->size != 1)) break;
}
debugnode("New node",new);
/* Now 'h' points to the first node that we still need to use,
* so our new node child pointer will point to it. */
raxNode **cp = raxNodeLastChildPtr(new);
memcpy(cp,&h,sizeof(h));
/* Fix parent link. */
if (parent) {
raxNode **parentlink = raxFindParentLink(parent,start);
memcpy(parentlink,&new,sizeof(new));
} else {
rax->head = new;
}
debugf("Compressed %d nodes, %d total bytes\n",
nodes, (int)comprsize);
}
}
raxStackFree(&ts);
return 1;
}
