Here is my implementation of threadsafe generic resizable hashmap without using stl containers:
#pragma once
#include <iomanip>
#include <exception>
#include <mutex>
#include <condition_variable>
/*
* wrapper for items stored in the map
*/
template<typename K, typename V>
class HashItem {
public:
HashItem(K key, V value) {
this->key = key;
this->value = value;
this->nextItem = nullptr;
}
/*
* copy constructor
*/
HashItem(const HashItem & item) {
this->key = item.getKey();
this->value = item.getValue();
this->nextItem = nullptr;
}
void setNext(HashItem<K, V> * item) {
this->nextItem = item;
}
HashItem * getNext() {
return nextItem;
}
K getKey() {
return key;
}
V getValue() {
return value;
}
void setValue(V value) {
this->value = value;
}
private:
K key;
V value;
HashItem * nextItem;
};
/*
* template HashMap for storing items
* default hash function HF = std::hash<K>
*/
template <typename K, typename V, typename HF = std::hash<K>>
class HashMap {
public:
/*
* constructor
* @mSize specifies the bucket size og the map
*/
HashMap(std::size_t mSize) {
// lock initialization for single thread
std::lock_guard<std::mutex>lock(mtx);
if (mSize < 1)
throw std::exception("Number of buckets ust be greater than zero.");
mapSize = mSize;
numOfItems = 0;
// initialize
hMap = new HashItem<K, V> *[mapSize]();
}
/*
* for simplicity no copy constructor
* anyway we want test how different threads
* use same instance of the map
*/
HashMap(const HashMap & hmap) = delete;
/*
* inserts item
* replaces old value with the new one when item already exists
* @key key of the item
* @value value of the item
*/
void insert(const K & key, const V & value) {
std::lock_guard<std::mutex>lock(mtx);
insertHelper(this->hMap, this->mapSize, numOfItems, key, value);
condVar.notify_all();
}
/*
* erases item with key when siúch item exists
* @key of item to erase
*/
void erase(const K & key) {
std::lock_guard<std::mutex>lock(mtx);
// calculate the bucket where item must be inserted
std::size_t hVal = hashFunc(key) % mapSize;
HashItem<K, V> * prev = nullptr;
HashItem<K, V> * item = hMap[hVal];
while ((item != nullptr) && (item->getKey() != key)) {
prev = item;
item = item->getNext();
}
// no item found with the given key
if (item == nullptr) {
return;
}
else {
if (prev == nullptr) {
// item found is the first item in the bucket
hMap[hVal] = item->getNext();
}
else {
// item found in one of the entries in the bucket
prev->setNext(item->getNext());
}
delete item;
numOfItems--;
}
condVar.notify_all();
}
/*
* get element with the given key by reference
* @key is the key of item that has to be found
* @value is the holder where the value of item with key will be copied
*/
bool getItem(const K & key, V & value) const {
std::lock_guard<std::mutex>lock(mtx);
// calculate the bucket where item must be inserted
std::size_t hVal = hashFunc(key) % mapSize;
HashItem<K, V> * item = hMap[hVal];
while ((item != nullptr) && (item->getKey() != key))
item = item->getNext();
// item not found
if (item == nullptr) {
return false;
}
value = item->getValue();
return true;
}
/*
* get element with the given key by reference
* @key is the key of item that has to be found
* shows an example of thread waitung for some condition
* @value is the holder where the value of item with key will be copied
*/
bool getWithWait(const K & key, V & value) {
std::unique_lock<std::mutex>ulock(mtxForWait);
condVar.wait(ulock, [this] {return !this->empty(); });
// calculate the bucket where item must be inserted
std::size_t hVal = hashFunc(key) % mapSize;
HashItem<K, V> * item = hMap[hVal];
while ((item != nullptr) && (item->getKey() != key))
item = item->getNext();
// item not found
if (item == nullptr) {
return false;
}
value = item->getValue();
return true;
}
/*
* resizes the map
* creates new map on heap
* copies the elements into new map
* @newSize specifies new bucket size
*/
void resize(std::size_t newSize) {
std::lock_guard<std::mutex>lock(mtx);
if (newSize < 1)
throw std::exception("Number of buckets must be greater than zero.");
resizeHelper(newSize);
condVar.notify_all();
}
/*
* outputs all items of the map
*/
void outputMap() const {
std::lock_guard<std::mutex>lock(mtx);
if (numOfItems == 0) {
std::cout << "Map is empty." << std::endl << std::endl;
return;
}
std::cout << "Map contains " << numOfItems << " items." << std::endl;
for (std::size_t i = 0; i < mapSize; i++) {
HashItem<K, V> * item = hMap[i];
while (item != nullptr) {
std::cout << "Bucket: " << std::setw(3) << i << ", key: " << std::setw(3) << item->getKey() << ", value:" << std::setw(3) << item->getValue() << std::endl;
item = item->getNext();
}
}
std::cout << std::endl;
}
/*
* returns true when map has no items
*/
bool empty() const {
std::lock_guard<std::mutex>lock(mtx);
return numOfItems == 0;
}
void clear() {
std::lock_guard<std::mutex>lock(mtx);
deleteMap(hMap, mapSize);
numOfItems = 0;
hMap = new HashItem<K, V> *[mapSize]();
}
/*
* returns number of items stored in the map
*/
std::size_t size() const {
std::lock_guard<std::mutex>lock(mtx);
return numOfItems;
}
/*
* returns number of buckets
*/
std::size_t bucket_count() const {
std::lock_guard<std::mutex>lock(mtx);
return mapSize;
}
/*
* desctructor
*/
~HashMap() {
std::lock_guard<std::mutex>lock(mtx);
deleteMap(hMap, mapSize);
}
private:
std::size_t mapSize;
std::size_t numOfItems;
HF hashFunc;
HashItem<K, V> ** hMap;
mutable std::mutex mtx;
mutable std::mutex mtxForWait;
std::condition_variable condVar;
/*
* help method for inserting key, value item into the map hm
* mapSize specifies the size of the map, items - the number
* of stored items, will be incremented when insertion is completed
* @hm HashMap
* @mSize specifies number of buckets
* @items holds the number of items in hm, will be incremented when insertion successful
* @key - key of item to insert
* @value - value of item to insert
*/
void insertHelper(HashItem<K, V> ** hm, const std::size_t & mSize, std::size_t & items, const K & key, const V & value) {
std::size_t hVal = hashFunc(key) % mSize;
HashItem<K, V> * prev = nullptr;
HashItem<K, V> * item = hm[hVal];
while ((item != nullptr) && (item->getKey() != key)) {
prev = item;
item = item->getNext();
}
// inserting new item
if (item == nullptr) {
item = new HashItem<K, V>(key, value);
items++;
if (prev == nullptr) {
// insert new value as first item in the bucket
hm[hVal] = item;
}
else {
// append new item on previous in the same bucket
prev->setNext(item);
}
}
else {
// replace existing value
item->setValue(value);
}
}
/*
* help method to resize the map
* @newSize specifies new number of buckets
*/
void resizeHelper(std::size_t newSize) {
HashItem<K, V> ** newMap = new HashItem<K, V> *[newSize]();
std::size_t items = 0;
for (std::size_t i = 0; i < mapSize; i++) {
HashItem<K, V> * item = hMap[i];
while (item != nullptr) {
insertHelper(newMap, newSize, items, item->getKey(), item->getValue());
item = item->getNext();
}
}
deleteMap(hMap, mapSize);
hMap = newMap;
mapSize = newSize;
numOfItems = items;
newMap = nullptr;
}
/*
* help function for deleting the map hm
* @hm HashMap
* @mSize number of buckets in hm
*/
void deleteMap(HashItem<K, V> ** hm, std::size_t mSize) {
// delete all nodes
for (std::size_t i = 0; i < mSize; ++i) {
HashItem<K, V> * item = hm[i];
while (item != nullptr) {
HashItem<K, V> * prev = item;
item = item->getNext();
delete prev;
}
hm[i] = nullptr;
}
// delete the map
delete[] hm;
}
};
https://stackoverflow.com/questions/19143228
italiano
english
français
española
中国
日本の
العربية
Deutsch
한국어
Português
Russian