infinite loop with crypto.randomBytes() causing 100% CPU hang

[edef1c]

var crypto = require('crypto')
while (true)
  console.log(crypto.randomBytes(32).toString('hex'))

The process prints a bunch of random numbers (yay!) and then hangs badly (:cry:) at 100% CPU.
I'm not sure how to debug this.

[edef1c]

For reference, the equivalent async program runs fine:

var crypto = require('crypto')

;(function f() {
  crypto.randomBytes(32, function(err, bytes) {
    if (err) throw err
    console.log(bytes.toString('hex'))
    f()
  })
})()

[edef1c]

It actually appears to hang outside the crypto.randomBytes call:

var crypto = require('crypto')

for (var i = 0;; i++) {
  console.log(i + '+')
  crypto.randomBytes(32)
  console.log(i + '-')
}

This always hangs at a - line (often without printing a newline, oddly enough, though the rest of the line always comes through fine)
The amount of iterations after which it hangs appears to be fairly… random.

[brendanashworth]

What sort of system are you running on? crypto.randomBytes will hang if the system does not have enough entropy to generate the cryptographically secure data. However, it shouldn't hang for long. Does it hang indefinitely?

[micnic]

@nathan7 , I do not understand what do you expect from an infinite loop, calling synchronously and indefinitely console.log() and crypto.randomBytes() will block the garbage collector to do its job, will eat up all your memory and in the end it will hang

[Fishrock123]

Please see the note here: https://iojs.org/api/crypto.html#crypto_crypto_randombytes_size_callback

Your process is blocking and stalling because you are infinitely looping over it. crypto.randomBytes() does some under-the-hood stuff to get cryptographically strong random data, and will fail in this case. I don't think this is avoidable. Don't infinitely loop over it. :)

[edef1c]

I can get plenty of entropy from /dev/random with other methods, without getting 100% CPU usage.
Blocking is fine, it's what I asked for.

[micnic]

@nathan7 , please try this code on your machine:

while (true) {
  console.log('1234567890');
}

and make your conclusions, the problem is not in crypto.randomBytes() it is because you are using an infinite loop, if you need more data just increase the value of the needed random bytes

[rlidwka]

Does crypto.pseudoRandomBytes make any difference?

[micnic]

@rlidwka , no, reason: https://github.com/iojs/io.js/blob/v1.x/lib/crypto.js#L650

[edef1c]

@Fishrock123
Welp, my bad. That definitely shouldn't lead to indefinite lockups, though?

[Fishrock123]

@nathan7 an infinite loop will... infinitely loop. As fast as possible. I'm not really sure what you expect..?

Type while(true); into any web browser console and see what happens. They all lock up.

[edef1c]

@Fishrock123
They're supposed to keep executing the loop body indefinitely, not lock up without the body executing ever again.
while(true); is indeed "please lock up, possibly using 100% CPU".
"please give me a never-ending stream of random numbers" is a fine thing to ask a computer. It's allowed to pause waiting for entropy. Hanging at 100% CPU doing nothing useful is a rather different matter.