Description

Controls the number of simultaneous calls to a promise-returning function.

const cc = require('concurrent-control');

const controller = cc();

function Test(value) {
  console.info("Test",value,"enters");
  return new Promise((resolve,reject)=>{
    setTimeout(()=>{
      console.info("Test",value,"returns");
      resolve();
    },5000);
  });
}

function TestCaller(value) {
  controller(()=>{
    return Test(value);
  });
}

TestCaller(1);
TestCaller(2);

this produces:

Test 1 enters
Test 1 returns
Test 2 enters
Test 2 returns

Install

npm install concurrent-control --save

Documentation

The module exports a function to be called to create a controller.

// const concurrentControl = require('concurrent-control');
// var controller =

moduleFunction([options])

options: an integer representing the number of allowed simultaneous calls, or a function returning this number, or a function returning a Promise that resolves to this number. If options is omitted, the default value is 1, meaning the controlled code can be called once at a time.

Returns a function to be called every time the controlled code is to be invoked:

controller(fn[,unqueueFn])

fn: the function to be called in a controlled way

unqueueFn: callback function called right after the call has been queued and offers functions as parameters to remove the call from the queue, resulting in resolving or rejecting the controller Promise. Note that if the call has started or is being executed, it cannot be aborted this way.

Returns a Promise that will either resolve or reject as the result of the code being executed or un-queued.

Example:

function CallCode(param) {
  console.info("CallCode",param);
  controller(()=>{
    console.info("Code",param,"starting");
    return codeThatTakes3SecondsToResolve()
      .then(()=>{
        console.info("Code",param,"done");
      });
  },(resolve,reject)=>{
    console.info("Got unqueue handlers for",param);
    setTimeout(()=>{
      console.info("Aborting",param);
      reject(); // resolve() would also un-queue the call
    },5000);
  });
}
for(var i=1; i<=3; i++)
  (function(index) {
    CallCode(index)
      .then(function() {
        console.info("Call",index,"resolved");
      })
      .catch(function(err) {
        console.info("Call",index,"rejected");
      })
    })(i);

produces:

CallCode 1
CallCode 2
CallCode 3
Code 1 starting
Got abort handler for 2
Got abort handler for 3
Code 1 executed
Code 2 starting
Call 1 resolved
Aborting 2
Aborting 3
Call 3 rejected
Code 2 executed
Call 2 resolved

unqueueFn for call 1 is never invoked since the action starts immediately. When the un-queue reject function for call 2 is triggered, this call has already started so this has no effect. Call 3 never starts since it was un-queued before it started executing.