Asynchronous Lock

This package provides many locks for synchronizing asynchronous processes

Install

pnpm add asynchronous-lock

Why Need Lock

We must know why do we need locks in JavaScript which is a single-threaded language, here is an example

1. Mock a database that has two asynchronous functions read and write

   class Database {
     private count: number;
        
     private constructor() {
       this.count = 0;
     }
        
     static create(): Database {
       return new Database();
     }
        
     async read(): Promise<number> {
       return this.count;
     }
        
     async write(count: number) {
       this.count = count;
     }
   }

2. Define increase function that can increase count in database

   async function increase(database: Database) {
     const count = await database.read();
     await database.write(count + 1);
   }

3. Test asynchronously

   async function test() {
     const database = Database.create();
        
     await Promise.all([
       increase(database),
       increase(database),
       increase(database),
       increase(database),
       increase(database),
     ]);
        
     const count = await database.read();
     console.log(count); // Unexpected result 1 (expect to be 5)
   }

Asynchronous executions may cause unexpected result, that's why we need locks in JavaScript

Usage

• Semaphore: See Semaphore.spec.ts
• Mutex: See Mutex.spec.ts
• Selector: See Selector.spec.ts