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'use strict';
// Test to validate massive dns lookups do not block filesytem I/O
// (or any fast I/O). Prior to https://github.com/libuv/libuv/pull/1845
// few back-to-back dns lookups were sufficient to engage libuv
// threadpool workers in a blocking manner, throttling other work items
// that need pool resources. Start slow and fast I/Os together, make sure
// fast I/O can complete in at least in 1/100th of time for slow I/O.
// TEST TIME TO COMPLETION: ~5 seconds.
const common = require('../common');
const dns = require('dns');
const fs = require('fs');
const assert = require('assert');
const start = Date.now();
const slowIOmax = 100;
let slowIOcount = 0;
let fastIOdone = false;
let slowIOend, fastIOend;
function onResolve() {
slowIOcount++;
if (slowIOcount === slowIOmax) {
slowIOend = Date.now();
// Conservative expectation: finish disc I/O
// at least by when the net I/O completes.
assert.ok(fastIOdone,
'fast I/O was throttled due to threadpool congestion.');
// More realistic expectation: finish disc I/O at least within
// a time duration that is half of net I/O.
// Ideally the slow I/O should not affect the fast I/O as those
// have two different thread-pool buckets. However, this could be
// highly load / platform dependent, so don't be very greedy.
const fastIOtime = fastIOend - start;
const slowIOtime = slowIOend - start;
const expectedMax = slowIOtime / 2;
assert.ok(fastIOtime < expectedMax,
'fast I/O took longer to complete, ' +
`actual: ${fastIOtime}, expected: ${expectedMax}`);
}
}
for (let i = 0; i < slowIOmax; i++) {
// We need to refresh the domain string everytime,
// otherwise the TCP stack that cache the previous lookup
// returns result from memory, breaking all our Math.
dns.lookup(`${randomDomain()}.com`, {}, common.mustCall(onResolve));
}
fs.readFile(__filename, common.mustCall(() => {
fastIOend = Date.now();
fastIOdone = true;
}));
function randomDomain() {
const d = Buffer.alloc(10);
for (let i = 0; i < 10; i++)
d[i] = 97 + (Math.round(Math.random() * 13247)) % 26;
return d.toString();
}
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