asynchronous-semaphore

This is an ordinary semaphore implementation which is written in JavaScript's async/await semantic. This enables users to limit the number of their asynchronous process which are executed simultaneously. It also allows users to implement critical section especially when its capacity is 1.

  import { semaphore } from './index.mjs';
  // This is a simple `sleep` implementation.
  const sleep = (t)=>new Promise((res,rej)=>setTimeout(res,t));
  // Create an arbitrary procedure which consumes a specified amount of time.
  const createProc = (name,t)=>{
    // Return a closure which is asynchronously executed.
    return async ()=>{
      log( `begin ${name} (${t})` );
      await sleep(t);
      log( `end   ${name} (${t})` );
    };
  };

  const r = semaphore(); // Call without arguments. The default capacity is 1.
  await Promise.all([
    r.take( createProc('1',3000) ),
    r.take( createProc('2',3000) ),
    r.take( createProc('3',3000) ),
  ]);

  // Output :
  // begin 1 (3000)
  // end   1 (3000)
  // begin 2 (3000)
  // end   2 (3000)
  // begin 3 (3000)
  // end   3 (3000)

  // In this example, the capacity number is set to one; that is these closures
  // are also critical sections.

  const r = semaphore(2);
  await Promise.all([
    r.take( createProc('1',3000) ),
    r.take( createProc('2',3000) ),
    r.take( createProc('3',3000) ),
  ]);

  // begin 1 (3000)
  // begin 2 (3000)
  // end   1 (3000)
  // begin 3 (3000)
  // end   2 (3000)
  // end   3 (3000)

  // In this example, the capacity number is set to two.
  // Please note that the beginnings and the endings of job-1 and job-2 are
  // interchanged.

  const r = semaphore(3);
  await Promise.all([
    r.take( createProc('1',3000) ),
    r.take( createProc('2',3000) ),
    r.take( createProc('3',3000) ),
  ]);

  // begin 1 (3000)
  // begin 2 (3000)
  // begin 3 (3000)
  // end   1 (3000)
  // end   2 (3000)
  // end   3 (3000)

History

(Wed, 18 Oct 2023 21:39:07 +0900) Released v1.0.0

(Fri, 02 Feb 2024 17:22:50 +0900) Released v1.0.1

Add semaphore(1) as a global variable named critical_section.