container.h

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// Luanti
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2010-2013 celeron55, Perttu Ahola <celeron55@gmail.com>
 
#pragma once
 
#include "irrlichttypes.h"
#include "debug.h" // sanity_check
#include "exceptions.h"
#include "threading/mutex_auto_lock.h"
#include "threading/semaphore.h"
#include <list>
#include <vector>
#include <map>
#include <unordered_set>
#include <queue>
#include <cassert>
#include <limits>
 
/*
        Queue with unique values with fast checking of value existence
*/
 
template<typename Value>
class UniqueQueue
{
public:
 
        /*
        Does nothing if value is already queued.
        Return value:
        true: value added
        false: value already exists
        */
        bool push_back(const Value &value)
        {
                if (m_set.insert(value).second)
                {
                        m_queue.push(value);
                        return true;
                }
                return false;
        }
 
        void pop_front()
        {
                m_set.erase(m_queue.front());
                m_queue.pop();
        }
 
        const Value &front() const
        {
                return m_queue.front();
        }
 
        size_t size() const
        {
                return m_queue.size();
        }
 
        bool empty() const
        {
                return m_queue.empty();
        }
 
private:
        std::unordered_set<Value> m_set;
        std::queue<Value> m_queue;
};
 
/*
        Thread-safe map
*/
 
template<typename Key, typename Value>
class MutexedMap
{
public:
        MutexedMap() = default;
 
        void set(const Key &name, const Value &value)
        {
                MutexAutoLock lock(m_mutex);
                m_values[name] = value;
        }
 
        bool get(const Key &name, Value *result) const
        {
                MutexAutoLock lock(m_mutex);
                auto n = m_values.find(name);
                if (n == m_values.end())
                        return false;
                if (result)
                        *result = n->second;
                return true;
        }
 
        std::vector<Value> getValues() const
        {
                MutexAutoLock lock(m_mutex);
                std::vector<Value> result;
                result.reserve(m_values.size());
                for (auto it = m_values.begin(); it != m_values.end(); ++it)
                        result.push_back(it->second);
                return result;
        }
 
        void clear()
        {
                MutexAutoLock lock(m_mutex);
                m_values.clear();
        }
 
private:
        std::map<Key, Value> m_values;
        mutable std::mutex m_mutex;
};
 
 
/*
        Thread-safe double-ended queue
*/
 
template<typename T>
class MutexedQueue
{
public:
        template<typename Key, typename U, typename Caller, typename CallerData>
        friend class RequestQueue;
 
        MutexedQueue() = default;
 
        bool empty() const
        {
                MutexAutoLock lock(m_mutex);
                return m_queue.empty();
        }
 
        void push_back(const T &t)
        {
                MutexAutoLock lock(m_mutex);
                m_queue.push_back(t);
                m_signal.post();
        }
 
        void push_back(T &&t)
        {
                MutexAutoLock lock(m_mutex);
                m_queue.push_back(std::move(t));
                m_signal.post();
        }
 
        /* this version of pop_front returns an empty element of T on timeout.
        * Make sure default constructor of T creates a recognizable "empty" element
        */
        T pop_frontNoEx(u32 wait_time_max_ms)
        {
                if (m_signal.wait(wait_time_max_ms)) {
                        MutexAutoLock lock(m_mutex);
 
                        T t = std::move(m_queue.front());
                        m_queue.pop_front();
                        return t;
                }
 
                return T();
        }
 
        T pop_front(u32 wait_time_max_ms)
        {
                if (m_signal.wait(wait_time_max_ms)) {
                        MutexAutoLock lock(m_mutex);
 
                        T t = std::move(m_queue.front());
                        m_queue.pop_front();
                        return t;
                }
 
                throw ItemNotFoundException("MutexedQueue: queue is empty");
        }
 
        T pop_frontNoEx()
        {
                m_signal.wait();
 
                MutexAutoLock lock(m_mutex);
 
                T t = std::move(m_queue.front());
                m_queue.pop_front();
                return t;
        }
 
        T pop_back(u32 wait_time_max_ms=0)
        {
                if (m_signal.wait(wait_time_max_ms)) {
                        MutexAutoLock lock(m_mutex);
 
                        T t = std::move(m_queue.back());
                        m_queue.pop_back();
                        return t;
                }
 
                throw ItemNotFoundException("MutexedQueue: queue is empty");
        }
 
        /* this version of pop_back returns an empty element of T on timeout.
        * Make sure default constructor of T creates a recognizable "empty" element
        */
        T pop_backNoEx(u32 wait_time_max_ms)
        {
                if (m_signal.wait(wait_time_max_ms)) {
                        MutexAutoLock lock(m_mutex);
 
                        T t = std::move(m_queue.back());
                        m_queue.pop_back();
                        return t;
                }
 
                return T();
        }
 
        T pop_backNoEx()
        {
                m_signal.wait();
 
                MutexAutoLock lock(m_mutex);
 
                T t = std::move(m_queue.back());
                m_queue.pop_back();
                return t;
        }
 
        auto iterLocked()
        {
                return IterationHelper(this);
        }
 
protected:
        // Helper class that allows direct access to the queue with locking
        struct IterationHelper {
                friend class MutexedQueue<T>;
                ~IterationHelper() {
                        q->getMutex().unlock();
                        q->getSignal().post(); // assume modified
                }
 
                auto begin() { return q->getQueue().begin(); }
                auto end() { return q->getQueue().end(); }
 
                auto erase(typename std::deque<T>::iterator it) {
                        return q->getQueue().erase(it);
                }
 
        private:
                IterationHelper(MutexedQueue<T> *parent) : q(parent) {
                        q->getMutex().lock();
                }
 
                MutexedQueue<T> *q;
        };
 
        std::mutex &getMutex() { return m_mutex; }
        Semaphore &getSignal() { return m_signal; }
 
        std::deque<T> &getQueue() { return m_queue; }
 
        std::deque<T> m_queue;
        mutable std::mutex m_mutex;
        Semaphore m_signal;
};
 
/*
        LRU cache
*/
 
template<typename K, typename V>
class LRUCache
{
public:
        LRUCache(size_t limit, void (*cache_miss)(void *data, const K &key, V *dest),
                        void *data)
        {
                setLimit(limit);
                m_cache_miss = cache_miss;
                m_cache_miss_data = data;
        }
 
        void setLimit(size_t limit)
        {
                m_limit = std::max<size_t>(1, limit);
                invalidate();
        }
 
        void invalidate()
        {
                m_map.clear();
                m_queue.clear();
        }
 
        const V *lookupCache(const K &key)
        {
                auto it = m_map.find(key);
                const V *ret;
                if (it != m_map.end()) {
                        // found!
                        cache_entry &entry = it->second;
 
                        ret = &entry.second;
 
                        // update the usage information
                        if (entry.first != m_queue.begin()) {
                                m_queue.erase(entry.first);
                                m_queue.push_front(key);
                                entry.first = m_queue.begin();
                        }
                } else {
                        // cache miss -- enter into cache
                        cache_entry &entry = m_map[key];
                        m_cache_miss(m_cache_miss_data, key, &entry.second);
                        ret = &entry.second;
 
                        // delete old entries
                        if (m_queue.size() == m_limit) {
                                const K &id = m_queue.back();
                                m_map.erase(id);
                                m_queue.pop_back();
                        }
 
                        m_queue.push_front(key);
                        entry.first = m_queue.begin();
                }
                return ret;
        }
 
private:
        typedef typename std::pair<typename std::list<K>::iterator, V> cache_entry;
        typedef std::map<K, cache_entry> cache_type;
 
        void (*m_cache_miss)(void *data, const K &key, V *dest);
        void *m_cache_miss_data;
        size_t m_limit;
 
        cache_type m_map;
        // we can't use std::deque here, because its iterators get invalidated
        std::list<K> m_queue;
};
 
/*
        Map that can be safely modified (insertion, deletion) during iteration
        Caveats:
        - you cannot insert null elements
        - you have to check for null elements during iteration, those are ones already deleted
        - size() and empty() don't work during iteration
        - not thread-safe in any way
 
        How this is implemented:
        - there are two maps: new and real
        - if inserting during iteration, the value is inserted into the "new" map
        - if deleting during iteration, the value is set to null (to be GC'd later)
        - when iteration finishes the "new" map is merged into the "real" map
*/
 
template<typename K, typename V>
class ModifySafeMap
{
public:
        // this allows bare pointers but also e.g. std::unique_ptr
        static_assert(std::is_default_constructible<V>::value,
                "Value type must be default constructible");
        static_assert(std::is_constructible<bool, V>::value,
                "Value type must be convertible to bool");
        static_assert(std::is_move_assignable<V>::value,
                "Value type must be move-assignable");
 
        typedef K key_type;
        typedef V mapped_type;
 
        ModifySafeMap() {
                // the null value must convert to false and all others to true, but
                // we can't statically check the latter.
                sanity_check(!null_value);
        }
        ~ModifySafeMap() {
                assert(!m_iterating);
        }
 
        // possible to implement but we don't need it
        DISABLE_CLASS_COPY(ModifySafeMap)
        ALLOW_CLASS_MOVE(ModifySafeMap)
 
        const V &get(const K &key) const {
                if (m_iterating) {
                        auto it = m_new.find(key);
                        if (it != m_new.end())
                                return it->second;
                }
                auto it = m_values.find(key);
                // This conditional block was converted from a ternary to ensure no
                // temporary values are created in evaluating the return expression,
                // which could cause a dangling reference.
                if (it != m_values.end())
                        return it->second;
                else
                        return null_value;
        }
 
        void put(const K &key, const V &value) {
                if (!value) {
                        assert(false);
                        return;
                }
                if (m_iterating) {
                        auto it = m_values.find(key);
                        if (it != m_values.end()) {
                                it->second = V();
                                m_garbage++;
                        }
                        m_new[key] = value;
                } else {
                        m_values[key] = value;
                }
        }
 
        void put(const K &key, V &&value) {
                if (!value) {
                        assert(false);
                        return;
                }
                if (m_iterating) {
                        auto it = m_values.find(key);
                        if (it != m_values.end()) {
                                it->second = V();
                                m_garbage++;
                        }
                        m_new[key] = std::move(value);
                } else {
                        m_values[key] = std::move(value);
                }
        }
 
        V take(const K &key) {
                V ret = V();
                if (m_iterating) {
                        auto it = m_new.find(key);
                        if (it != m_new.end()) {
                                ret = std::move(it->second);
                                m_new.erase(it);
                        }
                }
                auto it = m_values.find(key);
                if (it == m_values.end())
                        return ret;
                if (!ret)
                        ret = std::move(it->second);
                if (m_iterating) {
                        it->second = V();
                        m_garbage++;
                } else {
                        m_values.erase(it);
                }
                return ret;
        }
 
        bool remove(const K &key) {
                return !!take(key);
        }

        size_t size() const {
                if (m_iterating) {
                        // This is by no means impossible to determine, it's just annoying
                        // to code and we happen to not need this.
                        return unknown;
                }
                assert(m_new.empty());
                if (m_garbage == 0)
                        return m_values.size();
                size_t n = 0;
                for (auto &it : m_values)
                        n += !it.second ? 0 : 1;
                return n;
        }

        bool empty() const {
                if (m_iterating)
                        return false; // maybe
                if (m_garbage == 0)
                        return m_values.empty();
                for (auto &it : m_values) {
                        if (!!it.second)
                                return false;
                }
                return true;
        }
 
        auto iter() { return IterationHelper(this); }
 
        void clear() {
                if (m_iterating) {
                        for (auto &it : m_values)
                                it.second = V();
                        m_garbage = m_values.size();
                } else {
                        m_values.clear();
                        m_garbage = 0;
                }
        }
 
        static inline const V null_value = V();
 
        // returned by size() if called during iteration
        static constexpr size_t unknown = static_cast<size_t>(-1);
 
protected:
        void merge_new() {
                assert(!m_iterating);
                if (!m_new.empty()) {
                        m_new.merge(m_values); // entries in m_new take precedence
                        m_values.clear();
                        std::swap(m_values, m_new);
                }
        }
 
        void collect_garbage() {
                assert(!m_iterating);
                if (m_values.size() < GC_MIN_SIZE || m_garbage < m_values.size() / 2)
                        return;
                for (auto it = m_values.begin(); it != m_values.end(); ) {
                        if (!it->second)
                                it = m_values.erase(it);
                        else
                                ++it;
                }
                m_garbage = 0;
        }
 
        struct IterationHelper {
                friend class ModifySafeMap<K, V>;
                ~IterationHelper() {
                        assert(m->m_iterating);
                        m->m_iterating--;
                        if (!m->m_iterating) {
                                m->merge_new();
                                m->collect_garbage();
                        }
                }
 
                auto begin() { return m->m_values.cbegin(); }
                auto end() { return m->m_values.cend(); }
 
        private:
                IterationHelper(ModifySafeMap<K, V> *parent) : m(parent) {
                        assert(m->m_iterating < std::numeric_limits<decltype(m_iterating)>::max());
                        m->m_iterating++;
                }
 
                ModifySafeMap<K, V> *m;
        };
 
private:
        std::map<K, V> m_values;
        std::map<K, V> m_new;
        unsigned int m_iterating = 0;
        // approximate amount of null-placeholders in m_values, reliable for != 0 tests
        size_t m_garbage = 0;
 
        static constexpr size_t GC_MIN_SIZE = 30;
};