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@bnoordhuis
Created September 28, 2023 19:13
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[node.js] count active promises via the V8 inspector
"use strict"
const inspector = require("node:inspector/promises")
const session = new inspector.Session()
session.connect()
countPromises(session).then(console.log)
async function countPromises(session) {
// resource management: put all results in an object group
const objectGroup = crypto.randomUUID()
// get reference to global Promise object prototype
const {result:{objectId:promisePrototypeOID}} = await session.post(
"Runtime.evaluate",
{objectGroup, expression:"Promise.prototype"})
// get reference to array holding all promises
const {objects:{objectId:promisesArrayOID}} = await session.post(
"Runtime.queryObjects",
{objectGroup, prototypeObjectId:promisePrototypeOID})
// get contents of array; disable preview for performance reasons
const {result} = await session.post(
"Runtime.getProperties",
{objectId:promisesArrayOID, ownProperties:true, generatePreview:false})
// free resources, don't wait for completion
session.post("Runtime.releaseObjectGroup", {objectGroup})
// array includes "length" property, subtract one to correct
return result.length - 1
}
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