@thermopylae/lib.cache/dist/policies/eviction/segmented-lru.js

Modular cache.

import { number } from '@thermopylae/lib.utils';
import { DoublyLinkedList } from "../../data-structures/list/doubly-linked.js";
import { createException } from "../../error.js";
const SEGMENT_SYM = Symbol('SEGMENT_SYM');
class SegmentedLRUEvictionPolicy {
    segments;
    deleteFromCache;
    constructor(cacheMaxCapacity, protectedOverProbationRatio = 0.7) {
        if (cacheMaxCapacity < 2) {
            throw createException("INVALID_CACHE_MAX_CAPACITY" , `Capacity needs to be at least 2. Given: ${cacheMaxCapacity}.`);
        }
        const protectedSegmentSize = Math.round(number.percentage(cacheMaxCapacity, protectedOverProbationRatio) 
        );
        if (protectedSegmentSize < 1) {
            const context = { cacheMaxCapacity, protectedOverProbationRatio, protectedSegmentSize };
            throw createException("INVALID_PROTECTED_SEGMENT_SIZE" , `Protected segment size needs to be at least 1. Context: ${JSON.stringify(context)}.`);
        }
        this.segments = {
            [1 ]: {
                capacity: protectedSegmentSize,
                items: new DoublyLinkedList()
            },
            [0 ]: {
                capacity: cacheMaxCapacity - protectedSegmentSize,
                items: new DoublyLinkedList()
            }
        };
        if (this.segments[0 ].capacity < 1) {
            const context = {
                cacheMaxCapacity,
                protectedOverProbationRatio,
                protectedSegmentSize,
                probationSegmentSize: this.segments[0 ].capacity
            };
            throw createException("INVALID_PROBATION_SEGMENT_SIZE" , `Probation segment size needs to be at least 1. Context: ${JSON.stringify(context)}.`);
        }
    }
    get size() {
        let size = 0;
        for (const segment of Object.keys(this.segments)) {
            size += this.segments[segment].items.size;
        }
        return size;
    }
    get mostRecent() {
        return this.getEntryFrom('head');
    }
    get leastRecent() {
        return this.getEntryFrom('tail');
    }
    onHit(entry) {
        this.promote(entry);
        return 1 ;
    }
    onMiss() {
        return undefined;
    }
    onSet(entry) {
        this.demote(entry);
    }
    onUpdate() {
        return undefined;
    }
    onDelete(entry) {
        this.segments[entry[SEGMENT_SYM]].items.remove(entry);
        entry[SEGMENT_SYM] = undefined; 
    }
    onClear() {
        for (const segment of Object.keys(this.segments)) {
            this.segments[segment].items.clear();
        }
    }
    setDeleter(deleter) {
        this.deleteFromCache = deleter;
    }
    isFull(segment) {
        return this.segments[segment].items.size === this.segments[segment].capacity;
    }
    demote(entry) {
        if (this.isFull(0 )) {
            this.deleteFromCache(this.segments[0 ].items.tail);
        }
        this.segments[0 ].items.unshift(entry);
        entry[SEGMENT_SYM] = 0 ;
    }
    promote(entry) {
        switch (entry[SEGMENT_SYM]) {
            case 0 :
                this.segments[0 ].items.remove(entry);
                if (this.isFull(1 )) {
                    const tail = this.segments[1 ].items.tail;
                    this.segments[1 ].items.remove(tail);
                    this.demote(tail);
                }
                this.segments[1 ].items.unshift(entry);
                entry[SEGMENT_SYM] = 1 ;
                break;
            case 1 :
                this.segments[1 ].items.toFront(entry);
                break;
            default:
                throw createException("UNKNOWN_SEGMENT_TYPE" , `Unknown segment type: ${entry[SEGMENT_SYM]} found in entry: ${JSON.stringify(entry)}.`);
        }
    }
    getEntryFrom(pos) {
        if (this.segments[1 ].items[pos] == null) {
            if (this.segments[0 ].items[pos] == null) {
                return null;
            }
            return this.segments[0 ].items[pos];
        }
        return this.segments[1 ].items[pos];
    }
}
export { SegmentedLRUEvictionPolicy, SEGMENT_SYM };