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https://github.com/mongodb/mongo.git
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134 lines
3.5 KiB
C++
134 lines
3.5 KiB
C++
/**
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* Copyright (C) 2008 10gen Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License, version 3,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/* hashtab.h
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Simple, fixed size hash table. Darn simple.
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Uses a contiguous block of memory, so you can put it in a memory mapped file very easily.
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*/
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#pragma once
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#include "../stdafx.h"
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#include <map>
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namespace mongo {
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#pragma pack(1)
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/* you should define:
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int Key::hash() return > 0 always.
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*/
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template <
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class Key,
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class Type
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>
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class HashTable {
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public:
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const char *name;
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struct Node {
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int hash;
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Key k;
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Type value;
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bool inUse() {
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return hash != 0;
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}
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void setUnused() {
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hash = 0;
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}
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} *nodes;
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int n;
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int _find(const Key& k, bool& found) {
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found = false;
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int h = k.hash();
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int i = h % n;
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int start = i;
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int chain = 0;
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while ( 1 ) {
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if ( !nodes[i].inUse() ) {
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return i;
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}
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if ( nodes[i].hash == h && nodes[i].k == k ) {
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found = true;
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return i;
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}
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chain++;
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i = (i+1) % n;
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if ( i == start ) {
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out() << "warning: hashtable is full " << name << endl;
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return -1;
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}
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if ( chain == 200 )
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out() << "warning: hashtable long chain " << name << endl;
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}
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}
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public:
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/* buf must be all zeroes on initialization. */
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HashTable(void *buf, int buflen, const char *_name) : name(_name) {
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int m = sizeof(Node);
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// out() << "hashtab init, buflen:" << buflen << " m:" << m << endl;
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n = buflen / m;
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if ( (n & 1) == 0 )
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n--;
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nodes = (Node *) buf;
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assert( sizeof(Node) == 628 );
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//out() << "HashTable() " << _name << " sizeof(node):" << sizeof(Node) << " n:" << n << endl;
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}
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Type* get(const Key& k) {
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bool found;
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int i = _find(k, found);
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if ( found )
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return &nodes[i].value;
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return 0;
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}
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void kill(const Key& k) {
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bool found;
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int i = _find(k, found);
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if ( i >= 0 && found ) {
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nodes[i].k.kill();
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nodes[i].setUnused();
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}
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}
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void put(const Key& k, const Type& value) {
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bool found;
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int i = _find(k, found);
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if ( i < 0 )
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return;
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if ( !found ) {
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nodes[i].k = k;
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nodes[i].hash = k.hash();
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}
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else {
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assert( nodes[i].hash == k.hash() );
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}
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nodes[i].value = value;
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}
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};
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#pragma pack()
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} // namespace mongo
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