source: src/Common/PersistentMap.h @ 982f95d

//
// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// PersistentMap.h --
//
// Author           : Aaron B. Moss
// Created On       : Wed Jun 13 16:31:00 2018
// Last Modified By : Aaron B. Moss
// Last Modified On : Wed Jun 13 16:31:00 2018
// Update Count     : 1
//

#pragma once

#include <cassert>
#include <cstddef>
#include <functional>
#include <unordered_map>
#include <utility>

#include "GC.h"

/// Wraps a hash table in a persistent data structure, using a technique based 
/// on the persistent array in Conchon & Filliatre "A Persistent Union-Find 
/// Data Structure"

template<typename Key, typename Val, 
         typename Hash = std::hash<Key>, typename Eq = std::equal_to<Key>>
class PersistentMap : public GC_Object {
public:
        /// Type of this class
        using Self = PersistentMap<Key, Val, Hash, Eq>;

        /// Types of version nodes
        enum Mode { 
                BASE,  ///< Root node of version tree
                REM,   ///< Key removal node
                INS,   ///< Key update node
                UPD    ///< Key update node
        };

private:
        /// Type of underlying hash table
        using Base = std::unordered_map<Key, Val, Hash, Eq>;
        
        /// Node inserted into underlying map
        struct Ins {
                Self* base;  ///< Modified map
                Key key;     ///< Key inserted
                Val val;     ///< Value stored

                template<typename K, typename V>
                Ins(Self* b, K&& k, V&& v) : base(b), key(std::forward<K>(k)), val(std::forward<V>(v)) {}
        };

        /// Node removed from underlying map
        struct Rem {
                Self* base;  ///< Modified map
                Key key;     ///< Key removed

                template<typename K>
                Rem(Self* b, K&& k) : base(b), key(std::forward<K>(k)) {}
        };

        /// Underlying storage
        union Data {
                char def;
                Base base;
                Ins ins;
                Rem rem;

                Data() : def('\0') {}
                ~Data() {}
        } data;

        // Mode of node
        mutable Mode mode;

        /// get mutable reference as T
        template<typename T>
        T& as() { return reinterpret_cast<T&>(data); }

        /// get const reference as T
        template<typename T>
        const T& as() const { return reinterpret_cast<const T&>(data); }

        /// get rvalue reference as T
        template<typename T>
        T&& take_as() { return std::move(as<T>()); }

        /// initialize as T
        template<typename T, typename... Args>
        void init( Args&&... args ) {
                new( &as<T>() ) T { std::forward<Args>(args)... };
        }

        /// reset as current mode
        void reset() {
                switch( mode ) {
                        case BASE:          as<Base>().~Base(); break;
                        case REM:           as<Rem>().~Rem();   break;
                        case INS: case UPD: as<Ins>().~Ins();   break;
                        default: assertf(false, "invalid mode");
                }
        }

        /// reset as base
        void reset_as_base() { 
                assertf( mode == BASE, "can only reset_as_base() on BASE" );
                as<Base>().~Base();
        }

        PersistentMap( Mode m, Base&& b ) : data(), mode(m) {
                assertf(m == BASE, "invalid mode");
                init<Base>(std::move(b));
        }

        template<typename K, typename V>
        PersistentMap( Mode m, const Self* o, K&& k, V&& v ) : data(), mode(m) {
                assertf(m == INS || m == UPD, "invalid mode");
                init<Ins>(o, std::forward<K>(k), std::forward<V>(v));
        }

        template<typename K>
        PersistentMap( Mode m, const Self* o, K&& k ) : data(), mode(m) {
                assertf(m == REM, "invalid mode");
                init<Rem>(o, std::forward<K>(k));
        }

protected:
        void trace(const GC& gc) const {
                switch( mode ) {
                        case BASE: {
                                for (const auto& entry : as<Base>()) {
                                        gc << entry.first << entry.second;
                                }
                                return;
                        }
                        case REM: {
                                const Rem& self = as<Rem>();
                                gc << self.base << self.key;
                                return;
                        }
                        case INS: case UPD: {
                                const Ins& self = as<Ins>();
                                gc << self.base << self.key << self.val;
                                return;
                        }
                        default: assertf(false, "invalid mode");
                }
        }

public:
        using size_type = std::size_t;

        using iterator = typename Base::const_iterator;

        PersistentMap() : data(), mode(BASE) { init<Base>(); }

        PersistentMap( const Self& o ) = delete;

        Self& operator= ( const Self& o ) = delete;

        ~PersistentMap() { reset(); }

        /// reroot persistent map at current node
        void reroot() const {
                // recursive base case
                if ( mode == BASE ) return;
                
                // reroot base
                Self* mut_this = const_cast<Self*>(this);
                Self* base = ( mode == REM ) ? mut_this->as<Rem>().base : mut_this->as<Ins>().base;
                base->reroot();
                assertf(base->mode == BASE, "reroot results in base");

                // take map out of base
                Base base_map = base->take_as<Base>();
                base->reset_as_base();

                // switch base to inverse of self and mutate base map
                switch ( mode ) {
                        case REM: {
                                Rem& self = mut_this->as<Rem>();
                                auto it = base_map.find( self.key );
                                assertf( it != base_map.end(), "removed node must exist in base");

                                base->init<Ins>( mut_this, std::move(self.key), std::move(it->second) );
                                base->mode = INS;

                                base_map.erase( it );
                                break;
                        }
                        case INS: {
                                Ins& self = mut_this->as<Ins>();

                                base->init<Rem>( mut_this, self.key );
                                base->mode = REM;

                                base_map.emplace( std::move(self.key), std::move(self.val) );
                                break;
                        }
                        case UPD: {
                                Ins& self = mut_this->as<Ins>();
                                auto it = base_map.find( self.key );
                                assertf( it != base_map.end(), "updated node must exist in base");

                                base->init<Ins>( mut_this, std::move(self.key), std::move(it->second) );
                                base->mode = UPD;

                                it->second = std::move(self.val);
                                break;
                        }
                        default: assertf(false, "invalid mode");
                }

                // set base map into self
                mut_this->reset();
                mut_this->init<Base>( std::move(base_map) );
                mode = BASE;
        }

private:
        /// Gets the base after rerooting at the current node
        const Base& rerooted() const {
                reroot();
                return as<Base>();
        }

public:
        /// true iff the map is empty
        bool empty() const { return rerooted().empty(); }

        /// Get number of entries in map
        size_type size() const { return rerooted().size(); }

        /// Get begin iterator for map; may be invalidated by calls to non-iteration functions 
        /// or functions on other maps in the same chain
        iterator begin() const { return rerooted().begin(); }

        /// Get end iterator for map; may be invalidated by calls to non-iteration functions 
        /// or functions on other maps in the same chain
        iterator end() const { return rerooted().end(); }

        /// Get underlying map iterator for value
        iterator find(const Key& k) const { return rerooted().find( k ); }

        /// Check if value is present
        size_type count(const Key& k) const { return rerooted().count( k ); }

        /// Get value; undefined behavior if not present
        const Val& get(const Key& k) const {
                const Base& self = rerooted();
                auto it = self.find( k );
                assertf(it != self.end(), "get target not present");
                return it->second;
        }

        /// Get value; returns default if not present
        template<typename V>
        Val get_or_default(const Key& k, V&& d) const {
                const Base& self = rerooted();
                auto it = self.find( k );
                if ( it == self.end() ) return d;
                else return it->second;
        }

        /// Set value, storing new map in output variable
        template<typename K, typename V>
        Self* set(K&& k, V&& v) {
                reroot();
                assertf(mode == BASE, "reroot results in base");

                // transfer map to new node
                Self* ret = new Self{ BASE, take_as<Base>() };
                reset_as_base();
                Base& base_map = ret->as<Base>();

                // check if this is update or insert
                auto it = base_map.find( k );
                if ( it == base_map.end() ) {
                        // set self to REM node and insert into base
                        init<Rem>( ret, k );
                        mode = REM;

                        base_map.emplace_hint( it, std::forward<K>(k), std::forward<V>(v) );
                } else {
                        // set self to UPD node and modify base
                        init<Ins>( ret, std::forward<K>(k), std::move(it->second) );
                        mode = UPD;

                        it->second = std::forward<V>(v);
                }

                return ret;
        }

        /// Remove value, storing new map in output variable; does nothing if key not in map
        Self* erase(const Key& k) {
                reroot();
                assertf(mode == BASE, "reroot results in base");

                // exit early if key does not exist in map
                if ( ! as<Base>().count( k ) ) return this;

                // transfer map to new node
                Self* ret = new Self{ BASE, take_as<Base>() };
                reset_as_base();
                Base& base_map = ret->as<Base>();

                // set self to INS node and remove from base
                init<Ins>( ret, k, base_map[k] );
                mode = INS;
                
                base_map.erase( k );

                return ret;
        }

        /// smart reference for indexing interface
        class Entry {
        friend PersistentMap;
                Self* base;
                const Key& key;

        public:
                Entry(Self* b, const Key& k) : base(b), key(k) {}

                /// Gets the underlying map instance
                Self* get_base() const { return base; }

                /// Gets the key
                const Key& get_key() const { return key; }

                /// Checks if the key exists in the map
                bool exists() const { return base->count(key); }

                /// Gets the value for the key (if it exists)
                const Val& get() const { return base->get(key); }

                /// Cast version of get
                operator const Val& () const { return base->get(key); }

                /// Sets the value into the key; returns entry pointing to new set
                template<typename V>
                Entry& set(V&& v) {
                        base = base->set(key, std::forward<V>(v));
                        return *this;
                }

                /// Assignment version of set
                template<typename V>
                Entry& operator= (V&& v) {
                        base = base->set(key, std::forward<V>(v));
                        return *this;
                }

                /// Gets value or initializes to new value from args
                template<typename... Args>
                Entry& get_or(Args&&... args) {
                        base = base->get_or(key, std::forward<Args>(args)...);
                        return *this;
                }
        };

        /// Gets smart reference to slot with given key
        Entry operator[] (const Key& k) { return { this, k }; }

        /// Gets Entry for key, initializing from args if not present
        template<typename... Args>
        Entry get_or_insert(const Key& k, Args&&... args) {
                Base& base_map = rerooted();

                // check already present
                if ( base_map.count(k) ) return { this, k };

                // otherwise insert based on parameters
                base_map.emplace( k, Val{ std::forward<Args>(args)... } );
                Self* ret = new Self{ BASE, std::move(base_map) };

                // update self to point to new base
                reset_as_base();
                init<Rem>( ret, k );
                mode = REM;

                // return entry for new base
                return { ret, k };
        }

        /// Get version node type
        Mode get_mode() const { return mode; }

        /// Get next version up the revision tree (self if base node)
        const Self* get_base() const {
                switch ( mode ) {
                        case BASE:          return this;
                        case REM:           return as<Rem>().base;
                        case INS: case UPD: return as<Ins>().base;
                        default: assertf(false, "invalid mode");
                }
        }

        /// Get key of revision node (undefined if called on base)
        const Key& get_key() const {
                switch ( mode ) {
                        case REM:           return as<Rem>().key;
                        case INS: case UPD: return as<Ins>().key;
                        default: assertf(false, "invalid mode for get_key()");
                }
        }

        /// Get value of insert/update revision node (undefined otherwise)
        const Val& get_val() const {
                switch ( mode ) {
                        case INS: case UPD: return as<Ins>().val;
                        default: assertf(false, "invalid mode for get_val()");
                }
        }
};

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