event_emitter_setImmediate_example.js

event_emitter_setImmediate_example.js

const {EventEmitter} = require('events');

const ee = new EventEmitter();

function log(...args) {
    console.log(Date.now() / 1000, ...args);
}

function blockingOperation() {
    log('-- Blocking operation has started');
    let acc = 0;
    for (let i = 0; i < 1000000000; i++) {
        acc += i;
    }

    log('-- Blocking operation has ended');
    return acc;
}

ee.on('blocking-handler', message => {
    log(`Blocking handler. Called inside listener: ${message}`);
    blockingOperation();
});

ee.on('non-blocking-handler', message => {
  log(`Blocking handler. Called inside listener: ${message}`);
  setImmediate(blockingOperation);
});

function execute(event, message) {
    log('Executor wants to emit message and to exit ASAP');
    ee.emit(event, message);
    log('Executor returns');
}

log('Begin blocking handler');
execute('blocking-handler', 'event1');
log('End of blocking handler');

console.log('-------------');

log('Begin non-blocking handler');
execute('non-blocking-handler', 'event2');
log('End of non-blocking handler');

/*
 1561967007.302 'Begin blocking handler'
 1561967007.305 'Executor wants to emit message and to exit ASAP'
 1561967007.306 'Blocking handler. Called inside listener: event1'
 1561967007.306 '-- Blocking operation has started'
 1561967008.345 '-- Blocking operation has ended'
 1561967008.345 'Executor returns'
 1561967008.345 'End of blocking handler'
 -------------
 1561967008.345 'Begin non-blocking handler'
 1561967008.345 'Executor wants to emit message and to exit ASAP'
 1561967008.345 'Blocking handler. Called inside listener: event2'
 1561967008.346 'Executor returns'
 1561967008.346 'End of non-blocking handler'
 1561967008.348 '-- Blocking operation has started'
 1561967011.354 '-- Blocking operation has ended'
 */