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arangodb/lib/Basics/skip-list.cpp

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////////////////////////////////////////////////////////////////////////////////
/// @brief generic skip list implementation
///
/// @file
///
/// DISCLAIMER
///
/// Copyright 2014 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
/// http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Max Neunhoeffer
/// @author Copyright 2014, ArangoDB GmbH, Cologne, Germany
/// @author Copyright 2013-2013, triAGENS GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////
#include "Basics/random.h"
#include "skip-list.h"
using namespace triagens::basics;
// -----------------------------------------------------------------------------
// --SECTION-- SKIP LIST
// -----------------------------------------------------------------------------
// -----------------------------------------------------------------------------
// --SECTION-- private functions
// -----------------------------------------------------------------------------
////////////////////////////////////////////////////////////////////////////////
/// @brief randomHeight, select a node height randomly
////////////////////////////////////////////////////////////////////////////////
static int randomHeight (void) {
int height = 1;
int count;
while (true) { // will be left by return when the right height is found
uint32_t r = TRI_UInt32Random();
for (count = 32; count > 0; count--) {
if (0 != (r & 1UL) || height == TRI_SKIPLIST_MAX_HEIGHT) return height;
r = r >> 1;
height++;
}
}
}
////////////////////////////////////////////////////////////////////////////////
/// @brief Allocation function for a node. If height is 0, then a
/// random height is taken.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::allocNode (int height) {
SkipListNode* newNode = new SkipListNode();
newNode->_doc = nullptr;
if (0 == height) {
newNode->_height = randomHeight();
}
else {
newNode->_height = height;
}
try {
newNode->_next = new SkipListNode*[newNode->_height];
}
catch (...) {
delete newNode;
throw;
}
for (int i = 0; i < newNode->_height; i++) {
newNode->_next[i] = nullptr;
}
newNode->_prev = nullptr;
_memoryUsed += sizeof(SkipListNode) +
sizeof(SkipListNode*) * newNode->_height;
return newNode;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief Free function for a node.
////////////////////////////////////////////////////////////////////////////////
void SkipList::freeNode (SkipListNode* node) {
// update memory usage
_memoryUsed -= sizeof(SkipListNode) +
sizeof(SkipListNode*) * node->_height;
delete[] node->_next;
delete node;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief lookupLess
/// The following function is the main search engine for our skiplists.
/// It is used in the insertion and removal functions. See below for
/// a tiny variation which is used in the right lookup function.
/// This function does the following:
/// The skiplist sl is searched for the largest document m that is less
/// than doc. It uses preorder comparison if cmp is SKIPLIST_CMP_PREORDER
/// and proper order comparison if cmp is SKIPLIST_CMP_TOTORDER. At the end,
/// (*pos)[0] points to the node containing m and *next points to the
/// node following (*pos)[0], or is nullptr if there is no such node. The
/// array *pos contains for each level lev in 0.._start->_height-1
/// at (*pos)[lev] the pointer to the node that contains the largest
/// document that is less than doc amongst those nodes that have height >
/// lev.
////////////////////////////////////////////////////////////////////////////////
int SkipList::lookupLess (void* doc,
SkipListNode* (*pos)[TRI_SKIPLIST_MAX_HEIGHT],
SkipListNode** next,
SkipListCmpType cmptype) const {
int lev;
int cmp = 0; // just in case to avoid undefined values
SkipListNode* cur;
cur = _start;
for (lev = _start->_height-1; lev >= 0; lev--) {
while (true) { // will be left by break
*next = cur->_next[lev];
if (nullptr == *next) {
break;
}
cmp = _cmp_elm_elm(_cmpdata, (*next)->_doc, doc, cmptype);
if (cmp >= 0) {
break;
}
cur = *next;
}
(*pos)[lev] = cur;
}
// Now cur == (*pos)[0] points to the largest node whose document
// is less than doc. *next is the next node and can be nullptr if there
// is none.
return cmp;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief lookupLessOrEq
/// The following function is nearly as LookupScript above, but
/// finds the largest document m that is less than or equal to doc.
/// It uses preorder comparison if cmp is SKIPLIST_CMP_PREORDER
/// and proper order comparison if cmp is SKIPLIST_CMP_TOTORDER. At the end,
/// (*pos)[0] points to the node containing m and *next points to the
/// node following (*pos)[0], or is nullptr if there is no such node. The
/// array *pos contains for each level lev in 0.._start->_height-1
/// at (*pos)[lev] the pointer to the node that contains the largest
/// document that is less than or equal to doc amongst those nodes
/// that have height > lev.
////////////////////////////////////////////////////////////////////////////////
int SkipList::lookupLessOrEq (void* doc,
SkipListNode* (*pos)[TRI_SKIPLIST_MAX_HEIGHT],
SkipListNode** next,
SkipListCmpType cmptype) const {
int lev;
int cmp = 0; // just in case to avoid undefined values
SkipListNode* cur;
cur = _start;
for (lev = _start->_height-1; lev >= 0; lev--) {
while (true) { // will be left by break
*next = cur->_next[lev];
if (nullptr == *next) {
break;
}
cmp = _cmp_elm_elm(_cmpdata, (*next)->_doc, doc, cmptype);
if (cmp > 0) {
break;
}
cur = *next;
}
(*pos)[lev] = cur;
}
// Now cur == (*pos)[0] points to the largest node whose document
// is less than or equal to doc. *next is the next node and can be nullptr
// is if there none.
return cmp;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief lookupKeyLess
/// We have two more very similar functions which look up documents if
/// only a key is given. This implies using the cmp_key_elm function
/// and using the preorder only. Otherwise, they behave identically
/// as the two previous ones.
////////////////////////////////////////////////////////////////////////////////
int SkipList::lookupKeyLess (void* key,
SkipListNode* (*pos)[TRI_SKIPLIST_MAX_HEIGHT],
SkipListNode** next) const {
int lev;
int cmp = 0; // just in case to avoid undefined values
SkipListNode* cur;
cur = _start;
for (lev = _start->_height-1; lev >= 0; lev--) {
while (true) { // will be left by break
*next = cur->_next[lev];
if (nullptr == *next) {
break;
}
cmp = _cmp_key_elm(_cmpdata, key, (*next)->_doc);
if (cmp <= 0) {
break;
}
cur = *next;
}
(*pos)[lev] = cur;
}
// Now cur == (*pos)[0] points to the largest node whose document is
// less than key in the preorder. *next is the next node and can be
// nullptr if there is none.
return cmp;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief lookupKeyLessOrEq
////////////////////////////////////////////////////////////////////////////////
int SkipList::lookupKeyLessOrEq (void* key,
SkipListNode* (*pos)[TRI_SKIPLIST_MAX_HEIGHT],
SkipListNode** next) const {
int lev;
int cmp = 0; // just in case to avoid undefined values
SkipListNode* cur;
cur = _start;
for (lev = _start->_height-1; lev >= 0; lev--) {
while (true) { // will be left by break
*next = cur->_next[lev];
if (nullptr == *next) {
break;
}
cmp = _cmp_key_elm(_cmpdata, key, (*next)->_doc);
if (cmp < 0) {
break;
}
cur = *next;
}
(*pos)[lev] = cur;
}
// Now cur == (*pos)[0] points to the largest node whose document is
// less than or equal to key in the preorder. *next is the next node
// and can be nullptr is if there none.
return cmp;
}
// -----------------------------------------------------------------------------
// --SECTION-- constructors and destructors
// -----------------------------------------------------------------------------
////////////////////////////////////////////////////////////////////////////////
/// @brief creates a new skiplist
///
/// Returns nullptr if allocation fails and a pointer to the skiplist
/// otherwise.
////////////////////////////////////////////////////////////////////////////////
SkipList::SkipList (SkipListCmpElmElm cmp_elm_elm,
SkipListCmpKeyElm cmp_key_elm,
void* cmpdata,
SkipListFreeFunc freefunc,
bool unique)
: _cmp_elm_elm(cmp_elm_elm), _cmp_key_elm(cmp_key_elm), _cmpdata(cmpdata),
_free(freefunc), _unique(unique), _nrUsed(0) {
// set initial memory usage
_memoryUsed = sizeof(SkipList);
_start = allocNode(TRI_SKIPLIST_MAX_HEIGHT);
// Note that this can throw
_end = _start;
_start->_height = 1;
_start->_next[0] = nullptr;
_start->_prev = nullptr;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief frees a skiplist and all its documents
////////////////////////////////////////////////////////////////////////////////
SkipList::~SkipList () {
SkipListNode* p;
SkipListNode* next;
// First call free for all documents and free all nodes other than start:
p = _start->_next[0];
while (nullptr != p) {
if (nullptr != _free) {
_free(p->_doc);
}
next = p->_next[0];
freeNode(p);
p = next;
}
freeNode(_start);
}
////////////////////////////////////////////////////////////////////////////////
/// @brief inserts a new document into a skiplist
///
/// Comparison is done using proper order comparison. If the skiplist
/// is unique then no two documents that compare equal in the
/// preorder can be inserted. Returns TRI_ERROR_NO_ERROR if all
/// is well, TRI_ERROR_OUT_OF_MEMORY if allocation failed and
/// TRI_ERROR_ARANGO_UNIQUE_CONSTRAINT_VIOLATED if the unique constraint
/// would have been violated by the insert or if there is already a
/// document in the skip list that compares equal to doc in the proper
/// total order. In the latter two cases nothing is inserted.
////////////////////////////////////////////////////////////////////////////////
int SkipList::insert (void* doc) {
int lev;
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next = nullptr; // to please the compiler
SkipListNode* newNode;
int cmp;
cmp = lookupLess(doc,&pos,&next,SKIPLIST_CMP_TOTORDER);
// Now pos[0] points to the largest node whose document is less than
// doc. next is the next node and can be nullptr if there is none. doc is
// in the skiplist iff next != nullptr and cmp == 0 and in this case it
// is stored at the node next.
if (nullptr != next && 0 == cmp) {
// We have found a duplicate in the proper total order!
return TRI_ERROR_ARANGO_UNIQUE_CONSTRAINT_VIOLATED;
}
// Uniqueness test if wanted:
if (_unique) {
if ((pos[0] != _start &&
0 == _cmp_elm_elm(_cmpdata,doc,pos[0]->_doc,SKIPLIST_CMP_PREORDER)) ||
(nullptr != next &&
0 == _cmp_elm_elm(_cmpdata,doc,next->_doc,SKIPLIST_CMP_PREORDER))) {
return TRI_ERROR_ARANGO_UNIQUE_CONSTRAINT_VIOLATED;
}
}
try {
newNode = allocNode(0);
}
catch (...) {
return TRI_ERROR_OUT_OF_MEMORY;
}
if (newNode->_height > _start->_height) {
// The new levels where not considered in the above search,
// therefore pos is not set on these levels.
for (lev = _start->_height; lev < newNode->_height; lev++) {
pos[lev] = _start;
}
// Note that _start is already initialised with nullptr to the top!
_start->_height = newNode->_height;
}
newNode->_doc = doc;
// Now insert between newNode and next:
newNode->_next[0] = pos[0]->_next[0];
pos[0]->_next[0] = newNode;
newNode->_prev = pos[0];
if (newNode->_next[0] == nullptr) {
// a new last node
_end = newNode;
}
else {
newNode->_next[0]->_prev = newNode;
}
// Now the element is successfully inserted, the rest is performance
// optimisation:
for (lev = 1; lev < newNode->_height; lev++) {
newNode->_next[lev] = pos[lev]->_next[lev];
pos[lev]->_next[lev] = newNode;
}
_nrUsed++;
return TRI_ERROR_NO_ERROR;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief removes a document from a skiplist
///
/// Comparison is done using proper order comparison.
/// Returns TRI_ERROR_NO_ERROR if all is well and
/// TRI_ERROR_ARANGO_DOCUMENT_NOT_FOUND if the document was not found.
/// In the latter two cases nothing is removed.
////////////////////////////////////////////////////////////////////////////////
int SkipList::remove (void* doc) {
int lev;
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next = nullptr; // to please the compiler
int cmp;
cmp = lookupLess(doc,&pos,&next,SKIPLIST_CMP_TOTORDER);
// Now pos[0] points to the largest node whose document is less than
// doc. next points to the next node and can be nullptr if there is none.
// doc is in the skiplist iff next != nullptr and cmp == 0 and in this
// case it is stored at the node next.
if (nullptr == next || 0 != cmp) {
return TRI_ERROR_ARANGO_DOCUMENT_NOT_FOUND;
}
if (nullptr != _free) {
_free(next->_doc);
}
// Now delete where next points to:
for (lev = next->_height-1; lev >= 0; lev--) {
// Note the order from top to bottom. The element remains in the
// skiplist as long as we are at a level > 0, only some optimisations
// in performance vanish before that. Only when we have removed it at
// level 0, it is really gone.
pos[lev]->_next[lev] = next->_next[lev];
}
if (next->_next[0] == nullptr) {
// We were the last, so adjust _end
_end = next->_prev;
}
else {
next->_next[0]->_prev = next->_prev;
}
freeNode(next);
_nrUsed--;
return TRI_ERROR_NO_ERROR;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief looks up doc in the skiplist using the proper order
/// comparison.
///
/// Only comparisons using the proper order are done. Returns nullptr
/// if doc is not in the skiplist.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::lookup (void* doc) const {
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next = nullptr; // to please the compiler
int cmp;
cmp = lookupLess(doc,&pos,&next,SKIPLIST_CMP_TOTORDER);
// Now pos[0] points to the largest node whose document is less than
// doc. next points to the next node and can be nullptr if there is none.
// doc is in the skiplist iff next != nullptr and cmp == 0 and in this
// case it is stored at the node next.
if (nullptr == next || 0 != cmp) {
return nullptr;
}
return next;
}
////////////////////////////////////////////////////////////////////////////////
/// @brief finds the last document that is less to doc in the preorder
/// comparison or the start node if none is.
///
/// Only comparisons using the preorder are done.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::leftLookup (void* doc) const {
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next;
lookupLess(doc,&pos,&next,SKIPLIST_CMP_PREORDER);
// Now pos[0] points to the largest node whose document is less than
// doc in the preorder. next points to the next node and can be nullptr
// if there is none. doc is in the skiplist iff next != nullptr and cmp
// == 0 and in this case it is stored at the node next.
return pos[0];
}
////////////////////////////////////////////////////////////////////////////////
/// @brief finds the last document that is less or equal to doc in
/// the preorder comparison or the start node if none is.
///
/// Only comparisons using the preorder are done.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::rightLookup (void* doc) const {
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next;
lookupLessOrEq(doc,&pos,&next,SKIPLIST_CMP_PREORDER);
// Now pos[0] points to the largest node whose document is less than
// or equal to doc in the preorder. next points to the next node and
// can be nullptr if there is none. doc is in the skiplist iff next !=
// nullptr and cmp == 0 and in this case it is stored at the node next.
return pos[0];
}
////////////////////////////////////////////////////////////////////////////////
/// @brief finds the last document whose key is less to key in the preorder
/// comparison or the start node if none is.
///
/// Only comparisons using the preorder are done using cmp_key_elm.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::leftKeyLookup (void* key) const {
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next;
lookupKeyLess(key,&pos,&next);
// Now pos[0] points to the largest node whose document is less than
// key in the preorder. next points to the next node and can be nullptr
// if there is none. doc is in the skiplist iff next != nullptr and cmp
// == 0 and in this case it is stored at the node next.
return pos[0];
}
////////////////////////////////////////////////////////////////////////////////
/// @brief finds the last document that is less or equal to doc in
/// the preorder comparison or the start node if none is.
///
/// Only comparisons using the preorder are done using cmp_key_elm.
////////////////////////////////////////////////////////////////////////////////
SkipListNode* SkipList::rightKeyLookup (void* key) const {
SkipListNode* pos[TRI_SKIPLIST_MAX_HEIGHT];
SkipListNode* next;
lookupKeyLessOrEq(key,&pos,&next);
// Now pos[0] points to the largest node whose document is less than
// or equal to key in the preorder. next points to the next node and
// can be nullptr if there is none. doc is in the skiplist iff next !=
// nullptr and cmp == 0 and in this case it is stored at the node next.
return pos[0];
}
// -----------------------------------------------------------------------------
// --SECTION-- END-OF-FILE
// -----------------------------------------------------------------------------
// Local Variables:
// mode: outline-minor
// outline-regexp: "/// @brief\\|/// {@inheritDoc}\\|/// @page\\|// --SECTION--\\|/// @\\}"
// End:
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