TypeError: Cannot read property 'length' of undefined

[TheDeveloper]

TypeError: Cannot read property 'length' of undefined
    at Function.self (/home/app/node_modules/memoizee/ext/async.js:88:67)

Seems similar to #13 except I'm not sure of what exact scenario triggers this.

In ext/async.js, It seems that cb is assumed to either be a function or an Array of functions from the waiting[id] property. However, somehow, occasionally waiting[id] seems to be undefined when this code runs causing cb to also be undefined, which throws the error when cb.length is called when the 'setasync' method is emitted.

Is there possibly some race condition going on here where once callback clears the waiting queue before another unexpectedly tries to run? Can you think of any possible reasons why cb could be undefined?

Observed on v0.3.5 and previous versions.

[medikoo]

@TheDeveloper are you using some custom normalizer? How memoization of function is configured?

[TheDeveloper]

Sorry, I should have mentioned. These are the options:

{
    async: true,
    primitive: true,
    maxAge: self.conf.ttl.memory,
    resolvers: [String],
    length: 1
  }

I only require a single string argument, the 'key'.

[medikoo]

And it's when using latest version?

[TheDeveloper]

Yes I got this today in an app running v0.3.5

[gabmontes]

While doing a deeper analysis of my code that ends up in #13 once in a while, I also found that it fails in the only memoized fn with 'primitive' set to 'true' as my original fn receives an array.

Anyway, as @TheDeveloper says, there should be some race condition out there, happening even in the last version.

[medikoo]

It'll be great to have some reproducible test case, but I'll try to work this out, having above info.

[TheDeveloper]

Agreed but due to their stochastic nature, it is very difficult to create a reproducible test case for a race condition.

Side thought - could this happen if the callback to the async operation is called more than once?

[TheDeveloper]

Thanks for looking into this, I'll test the changes!

[medikoo]

After analyzing the code, I was able to reproduce it with working test case. It was related to race condition issue that could happen after reapplying function with previously used arguments after clear/delete call.

Indeed fix applied at #13 addressed issue just partially, and didn't took into account possibility of repeated call with same id in case of primitive handling.

Published with v0.3.6

[gabmontes]

@medikoo thanks for addressing this! Will also test the new version.

@TheDeveloper thanks for your insights too!

[TheDeveloper]

Update: I am no longer seeing the exception in our logs 😄

[medikoo]

Great to hear that, I'm pretty sure applied fix is bulletproof :)