pip-services3-components-nodex/src/cache/MemoryCache.ts

Component definitions for Pip.Services in Node.js / ES2017

/** @module cache */
import { IReconfigurable } from 'pip-services3-commons-nodex';
import { ConfigParams } from 'pip-services3-commons-nodex';

import { ICache } from './ICache';
import { CacheEntry } from './CacheEntry';

/**
 * Cache that stores values in the process memory.
 * 
 * Remember: This implementation is not suitable for synchronization of distributed processes.
 * 
 * ### Configuration parameters ###
 * 
 * __options:__
 * - timeout:               default caching timeout in milliseconds (default: 1 minute)
 * - max_size:              maximum number of values stored in this cache (default: 1000)        
 *  
 * @see [[ICache]]
 * 
 * ### Example ###
 * 
 *     let cache = new MemoryCache();
 *     
 *     await cache.store("123", "key1", "ABC");
 *     ...
 *     let value = await cache.retrieve("123", "key1");
 *     // Result: "ABC"
 * 
 */
export class MemoryCache implements ICache, IReconfigurable {
    private _cache: any = {};
    private _count: number = 0;

    private _timeout: number = 60000;
    private _maxSize: number = 1000;

	/**
	 * Creates a new instance of the cache.
	 */
    public constructor() { }

	/**
     * Configures component by passing configuration parameters.
     * 
     * @param config    configuration parameters to be set.
	 */
    public configure(config: ConfigParams): void {
        this._timeout = config.getAsLongWithDefault("options.timeout", this._timeout);
        this._maxSize = config.getAsLongWithDefault("options.max_size", this._maxSize);
    }

	/**
	 * Clears component state.
	 * 
	 * @param correlationId 	(optional) transaction id to trace execution through call chain.
     * @param callback 			callback function that receives error or null no errors occured.
	 */
    private cleanup(): void {
        let oldest: CacheEntry = null;
        let now: number = new Date().getTime();
        this._count = 0;

        // Cleanup obsolete entries and find the oldest
        for (let prop in this._cache) {
            let entry: CacheEntry = <CacheEntry>this._cache[prop];
            // Remove obsolete entry
            if (entry.isExpired()) {
                delete this._cache[prop];
            }
            // Count the remaining entry 
            else {
                this._count++;
                if (oldest == null || oldest.getExpiration() > entry.getExpiration())
                    oldest = entry;
            }
        }

        // Remove the oldest if cache size exceeded maximum
        if (this._count > this._maxSize && oldest != null) {
            delete this._cache[oldest.getKey()];
            this._count--;
        }
    }

    /**
     * Retrieves cached value from the cache using its key.
     * If value is missing in the cache or expired it returns null.
     * 
     * @param correlationId     (optional) transaction id to trace execution through call chain.
     * @param key               a unique value key.
     * @returns                 the cached value or <code>null</code> if value wasn't found.
     */
    public async retrieve(correlationId: string, key: string): Promise<any> {
        if (key == null) {
            throw new Error('Key cannot be null');
        }

        // Get entry from the cache
        let entry: CacheEntry = <CacheEntry>this._cache[key];

        // Cache has nothing
        if (entry == null) {
            return null;
        }

        // Remove entry if expiration set and entry is expired
        if (this._timeout > 0 && entry.isExpired()) {
            delete this._cache[key];
            this._count--;
            return null;
        }

        return entry.getValue();
    }

	/**
     * Stores value in the cache with expiration time.
     * 
     * @param correlationId     (optional) transaction id to trace execution through call chain.
     * @param key               a unique value key.
     * @param value             a value to store.
     * @param timeout           expiration timeout in milliseconds.
     * @returns                 The value that was stored in the cache.
	 */
    public async store(correlationId: string, key: string, value: any, timeout: number): Promise<any> {
        if (key == null) {
            throw new Error('Key cannot be null');
        }

        // Get the entry
        let entry: CacheEntry = <CacheEntry>this._cache[key];

        // Shortcut to remove entry from the cache
        if (value == null) {
            if (entry != null) {
                delete this._cache[key];
                this._count--;
            }
            return value;
        }

        timeout = timeout != null && timeout > 0 ? timeout : this._timeout;

        // Update the entry
        if (entry) {
            entry.setValue(value, timeout);
        }
        // Or create a new entry 
        else {
            entry = new CacheEntry(key, value, timeout);
            this._cache[key] = entry;
            this._count++;
        }

        // Clean up the cache
        if (this._maxSize > 0 && this._count > this._maxSize) {
            this.cleanup();
        }

        return value;
    }

	/**
     * Removes a value from the cache by its key.
     * 
     * @param correlationId     (optional) transaction id to trace execution through call chain.
     * @param key               a unique value key.
	 */
    public async remove(correlationId: string, key: string): Promise<void> {
        if (key == null) {
            throw new Error('Key cannot be null');
        }

        // Get the entry
        let entry: CacheEntry = <CacheEntry>this._cache[key];

        // Remove entry from the cache
        if (entry != null) {
            delete this._cache[key];
            this._count--;
        }
    }

}