thread count change

test.js

process.env.UV_THREADPOOL_SIZE = 2;

const crypto = require('crypto');

const start = Date.now();
crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '1:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '2:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '3:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '4:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '5:', Date.now() - start );
});

// output
// 2: 1108
// 1: 1117
// 3: 2321
// 4: 2364
// 5: 3447