/* Remove the specified key. If 'deleted' is not NULL the pointed integer is
* set to 0 if the key was not found, to 1 if it was found and deleted.
*
* 从 zipmap 中删除包含给定 key 的节点。
*
* 如果 deleted 参数不为 NULL ，那么：
*
* 1) 如果因为 key 没找到而导致删除失败，那么将 *deleted 设为 0 。
*
* 2) 如果 key 找到了，并且成功将它删除了，那么将 *deleted 设为 1 。
*
* T = O(N^2)
*/
unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) {
unsigned int zmlen, freelen;
// T = O(N^2)
unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p) {
// 找到，进行删除
// 计算节点的总长
freelen = zipmapRawEntryLength(p);
// 移动内存，覆盖被删除的数据
// T = O(N)
memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
// 缩小 zipmap
// T = O(N)
zm = zipmapResize(zm, zmlen-freelen);
/* Decrease zipmap length */
// 减少 zipmap 的节点数量
// 注意，如果节点数量已经大于等于 ZIPMAP_BIGLEN
// 那么这里不会进行减少，只有在调用 zipmapLen 的时候
// 如果有需要的话，正确的节点数量才会被设置
// 具体请看 zipmapLen 的源码
if (zm[0] < ZIPMAP_BIGLEN) zm[0]--;
if (deleted) *deleted = 1;
} else {
if (deleted) *deleted = 0;
}
return zm;
}
/* Remove the specified key. If 'deleted' is not NULL the pointed integer is
* set to 0 if the key was not found, to 1 if it was found and deleted. */
unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) {
unsigned int zmlen, freelen;
unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p) {
freelen = zipmapRawEntryLength(p);
memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
zm = zipmapResize(zm, zmlen-freelen);
/* Decrease zipmap length */
if (zm[0] < ZIPMAP_BIGLEN) zm[0]--;
if (deleted) *deleted = 1;
} else {
if (deleted) *deleted = 0;
}
return zm;
}
/* 根据key删除指定的键值对 */
unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) {
unsigned int zmlen, freelen;
// 看判断该键值对是否在zipmap中，如果不存在则直接返回
unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p) {
// 下面三句代码执行删除操作，其实就是内存块的移动操作
freelen = zipmapRawEntryLength(p);
memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
zm = zipmapResize(zm, zmlen-freelen);
/* Decrease zipmap length */
if (zm[0] < ZIPMAP_BIGLEN) zm[0]--;
if (deleted) *deleted = 1;
} else {
if (deleted) *deleted = 0;
}
return zm;
}
/* Remove the specified key. If 'deleted' is not NULL the pointed integer is
* set to 0 if the key was not found, to 1 if it was found and deleted. */
unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) {
unsigned int zmlen, freelen;
unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p) {
// 返回当前元素的长度
freelen = zipmapRawEntryLength(p);
// 移动这个元素后面的内容,往前移动,连续内存的好处
memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
// 重新分配小的内存
zm = zipmapResize(zm, zmlen-freelen);
// 设置新的长度
/* Decrease zipmap length */
if (zm[0] < ZIPMAP_BIGLEN) zm[0]--;
if (deleted) *deleted = 1;
} else {
if (deleted) *deleted = 0;
}
return zm;
}
/* Set key to value, creating the key if it does not already exist.
* If 'update' is not NULL, *update is set to 1 if the key was
* already preset, otherwise to 0. */
unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) {
unsigned int zmlen, offset;
unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
unsigned int empty, vempty;
unsigned char *p;
freelen = reqlen;
if (update) *update = 0;
p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p == NULL) {
/* Key not found: enlarge */
zm = zipmapResize(zm, zmlen+reqlen);
p = zm+zmlen-1;
zmlen = zmlen+reqlen;
/* Increase zipmap length (this is an insert) */
if (zm[0] < ZIPMAP_BIGLEN) zm[0]++;
} else {
/* Key found. Is there enough space for the new value? */
/* Compute the total length: */
if (update) *update = 1;
freelen = zipmapRawEntryLength(p);
if (freelen < reqlen) {
/* Store the offset of this key within the current zipmap, so
* it can be resized. Then, move the tail backwards so this
* pair fits at the current position. */
offset = p-zm;
zm = zipmapResize(zm, zmlen-freelen+reqlen);
p = zm+offset;
/* The +1 in the number of bytes to be moved is caused by the
* end-of-zipmap byte. Note: the *original* zmlen is used. */
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen = zmlen-freelen+reqlen;
freelen = reqlen;
}
}
/* We now have a suitable block where the key/value entry can
* be written. If there is too much free space, move the tail
* of the zipmap a few bytes to the front and shrink the zipmap,
* as we want zipmaps to be very space efficient. */
empty = freelen-reqlen;
if (empty >= ZIPMAP_VALUE_MAX_FREE) {
/* First, move the tail <empty> bytes to the front, then resize
* the zipmap to be <empty> bytes smaller. */
offset = p-zm;
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen -= empty;
zm = zipmapResize(zm, zmlen);
p = zm+offset;
vempty = 0;
} else {
vempty = empty;
}
/* Just write the key + value and we are done. */
/* Key: */
p += zipmapEncodeLength(p,klen);
memcpy(p,key,klen);
p += klen;
/* Value: */
p += zipmapEncodeLength(p,vlen);
*p++ = vempty;
memcpy(p,val,vlen);
return zm;
}
/* 根据key设置value，如果key不存在则创建相应的键值对，参数update用来辨别更新操作和添加操作。 */
unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) {
unsigned int zmlen, offset;
// 计算存储key和value所需要的字节数
unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
unsigned int empty, vempty;
unsigned char *p;
/************************************************************************
* 下面这段代码用于在zipmap留出足够的空间来容纳新插入的键值对或新的value值，尚未写入
************************************************************************/
freelen = reqlen;
if (update) *update = 0;
// 在zipmap中查找key，函数返回后zmlen中保存了zipmap所占用的字节数。
p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p == NULL) {
/* Key not found: enlarge */
// 如果key指定的键值对不存在，则对zipmap扩容，为容纳新的键值对准备内存空间
// zipmapResize执行的是realloc操作
zm = zipmapResize(zm, zmlen+reqlen);
// 此时p指向扩容前zipmap的结尾符，将从这里添加新的键值对
p = zm+zmlen-1;
// 更新zipmap所占用的内存空间大小
zmlen = zmlen+reqlen;
/* Increase zipmap length (this is an insert) */
// 更新zipmap中保存的键值对数量，即zmlen字段
if (zm[0] < ZIPMAP_BIGLEN) zm[0]++;
} else {
/* Key found. Is there enough space for the new value? */
/* 找到可对应的键值对，执行更新操作。这里需要考虑value节点的空间大小是否能够容纳新值 */
/* Compute the total length: */
if (update) *update = 1;
// 求出旧value节点的空间大小
freelen = zipmapRawEntryLength(p);
if (freelen < reqlen) {
/* Store the offset of this key within the current zipmap, so
* it can be resized. Then, move the tail backwards so this
* pair fits at the current position. */
// 旧节点的空间太小，需要扩容操作，zipmapResize函数会重新分配空间，所以需要记录p指针的偏移量
offset = p-zm;
zm = zipmapResize(zm, zmlen-freelen+reqlen);
p = zm+offset;
/* The +1 in the number of bytes to be moved is caused by the
* end-of-zipmap byte. Note: the *original* zmlen is used. */
// 移动旧value节点以后的元素以确保有足够的空间容纳新值（ +1是将尾部结尾符一起移动）
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen = zmlen-freelen+reqlen;
freelen = reqlen;
}
}
/* We now have a suitable block where the key/value entry can
* be written. If there is too much free space, move the tail
* of the zipmap a few bytes to the front and shrink the zipmap,
* as we want zipmaps to be very space efficient. */
// freelen表示经上步骤后流出来的空余空间大小，reqlen表示插入或更新键值对所需要的空间，两者的差就是free字段的
// 的值，如果该值过大zipmap会自动调整。下面这段代码就是完成调整功能。
empty = freelen-reqlen;
if (empty >= ZIPMAP_VALUE_MAX_FREE) {
/* First, move the tail <empty> bytes to the front, then resize
* the zipmap to be <empty> bytes smaller. */
offset = p-zm;
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen -= empty;
zm = zipmapResize(zm, zmlen);
p = zm+offset;
vempty = 0;
} else {
vempty = empty;
}
/******************************************
* 下面的操作是讲key和value写入zipmap指定位置
*******************************************/
/* Just write the key + value and we are done. */
/* Key: */
// 对key的长度编码并写入zipmap中
p += zipmapEncodeLength(p,klen);
// 写入key字符串
memcpy(p,key,klen);
// 移动指针到value写入位置
p += klen;
/* Value: */
// 对value的长度编码并写入zipmap中
p += zipmapEncodeLength(p,vlen);
// 写入free字段
*p++ = vempty;
// 写入value
memcpy(p,val,vlen);
return zm;
}
/* Set key to value, creating the key if it does not already exist.
*
* 将 key 的值设置为 value ，如果 key 不存在于 zipmap 中，那么新创建一个。
*
* If 'update' is not NULL, *update is set to 1 if the key was
* already preset, otherwise to 0.
*
* 如果 update 不为 NULL ：
*
* 1) 那么在 key 已经存在时，将 *update 设为 1 。
*
* 2) 如果 key 未存在，将 *update 设为 0 。
*
* T = O(N^2)
*/
unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) {
unsigned int zmlen, offset;
// 计算节点所需的长度
unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
unsigned int empty, vempty;
unsigned char *p;
freelen = reqlen;
if (update) *update = 0;
// 按 key 在 zipmap 中查找节点
// T = O(N^2)
p = zipmapLookupRaw(zm,key,klen,&zmlen);
if (p == NULL) {
/* Key not found: enlarge */
// key 不存在，扩展 zipmap
// T = O(N)
zm = zipmapResize(zm, zmlen+reqlen);
p = zm+zmlen-1;
zmlen = zmlen+reqlen;
/* Increase zipmap length (this is an insert) */
if (zm[0] < ZIPMAP_BIGLEN) zm[0]++;
} else {
/* Key found. Is there enough space for the new value? */
/* Compute the total length: */
// 键已经存在，检查旧的值空间大小能否满足新值
// 如果不满足的话，扩展 zipmap 并移动数据
if (update) *update = 1;
// T = O(1)
freelen = zipmapRawEntryLength(p);
if (freelen < reqlen) {
/* Store the offset of this key within the current zipmap, so
* it can be resized. Then, move the tail backwards so this
* pair fits at the current position. */
// 如果已有空间不满足新值所需空间，那么对 zipmap 进行扩展
// T = O(N)
offset = p-zm;
zm = zipmapResize(zm, zmlen-freelen+reqlen);
p = zm+offset;
/* The +1 in the number of bytes to be moved is caused by the
* end-of-zipmap byte. Note: the *original* zmlen is used. */
// 向后移动数据，为节点空出足以存放新值的空间
// T = O(N)
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen = zmlen-freelen+reqlen;
freelen = reqlen;
}
}
/* We now have a suitable block where the key/value entry can
* be written. If there is too much free space, move the tail
* of the zipmap a few bytes to the front and shrink the zipmap,
* as we want zipmaps to be very space efficient. */
// 计算节点空余空间的长度，如果空余空间太大了，就进行缩短
empty = freelen-reqlen;
if (empty >= ZIPMAP_VALUE_MAX_FREE) {
/* First, move the tail <empty> bytes to the front, then resize
* the zipmap to be <empty> bytes smaller. */
offset = p-zm;
// 前移数据，覆盖空余空间
// T = O(N)
memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen -= empty;
// 缩小 zipmap ，移除多余的空间
// T = O(N)
zm = zipmapResize(zm, zmlen);
p = zm+offset;
vempty = 0;
} else {
vempty = empty;
}
/* Just write the key + value and we are done. */
/* Key: */
// 写入键
// T = O(N)
p += zipmapEncodeLength(p,klen);
memcpy(p,key,klen);
p += klen;
/* Value: */
// 写入值
// T = O(N)
p += zipmapEncodeLength(p,vlen);
*p++ = vempty;
memcpy(p,val,vlen);
return zm;
}
