Mutex.ts

//================================================================ 
/** @module std */
//================================================================
import { ILockable } from "./ILockable";

import { Queue } from "../container/Queue";
import { RangeError } from "../exception/RuntimeError";

/**
 * Mutex.
 * 
 * @author Jeongho Nam <http://samchon.org>
 */
export class Mutex implements ILockable
{
	/**
	 * @hidden
	 */
	private lock_count_: number;

	/**
	 * @hidden
	 */
	private resolvers_: Queue<IResolver>;

	/* ---------------------------------------------------------
		CONSTRUCTORS
	--------------------------------------------------------- */
	/**
	 * Default Constructor.
	 */
	public constructor()
	{
		this.lock_count_ = 0;
		this.resolvers_ = new Queue();
	}

	/* ---------------------------------------------------------
		LOCK & UNLOCK
	--------------------------------------------------------- */
	/**
	 * @inheritDoc
	 */
	public lock(): Promise<void>
	{
		return new Promise<void>(resolve =>
		{
			if (this.lock_count_++ === 0)
				resolve();
			else
				this.resolvers_.push(resolve);
		});
	}

	/**
	 * @inheritDoc
	 */
	public async try_lock(): Promise<boolean>
	{
		if (this.lock_count_ !== 0)
			return false; // HAVE LOCKED
		
		++this.lock_count_;
		return true;
	}

	/**
	 * @inheritDoc
	 */
	public async unlock(): Promise<void>
	{
		if (this.lock_count_ === 0)
			throw new RangeError("This mutex is free.");

		--this.lock_count_; // DECREASE LOCKED COUNT
		if (this.resolvers_.empty() === false)
		{
			let fn: IResolver = this.resolvers_.front();
			
			this.resolvers_.pop(); // POP FIRST
			fn(); // AND CALL LATER
		}
	}
}

/**
 * @hidden
 */
interface IResolver
{
	(): void;
}

export type mutex = Mutex;
export const mutex = Mutex;