Where are closure storing the captured variables ?

[chris...@meessen.net]

Hello,

Closure need space to store the captured variables. According to runtime.MemStats, it is not on the heap. Where are these variable stored ? On the stack ?

[Axel Wagner]

It depends a bit on escape analysis. I think the easiest way to reason about it is to say that they are stored in the `func` value. If the `func` value escapes, than so do the closed-over variables. If it doesn't (and the closed-over variables are not otherwise escaped) they don't. At least to an approximation.

The precise details of how closures are implemented are described in this document: https://docs.google.com/document/d/1bMwCey-gmqZVTpRax-ESeVuZGmjwbocYs1iHplK-cjo/pub

I don't think anything material has changed since then.

On Thu, Jul 6, 2023 at 2:35 AM chris...@meessen.net <chris...@meessen.net> wrote:

Hello,

Closure need space to store the captured variables. According to runtime.MemStats, it is not on the heap. Where are these variable stored ? On the stack ?

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[jake...@gmail.com]

In addition to Axel's useful info, whenever you are interested in what escapes to the 'heap', it  can be helpful to build with escape analyses output. Try using "go build  -gcflags=-m".