Feature request: snapshot and restore support

[yanjiew1]

Hi,

Would quickjs-ng be interested in supporting snapshot and restore for a JSRuntime or JSContext?

The idea is to save the state of a JavaScript environment and later restore it, instead of recreating and reinitializing the environment from scratch.

V8 supports custom startup snapshots, and Node.js also provides startup snapshot functionality. Snapshot/restore support in quickjs-ng could be useful for embedders as well as other environments that need fast startup or the ability to preserve and restore JavaScript runtime state.

Possible use cases include:

• fast startup from a pre-initialized environment
• checkpointing and restoring long-running workloads
• suspending and resuming JavaScript environments
• quickly creating or resetting isolated JavaScript environments

Would this kind of feature be within the scope of quickjs-ng?

[bnoordhuis]

Would this kind of feature be within the scope of quickjs-ng?

Yes, if it doesn't add too much code and complexity. You'll have to tackle unresolved issues like #977 first, though. There's likely a long tail of such issues.

You'll also have to think about if and how to (de)serialize embedder objects (JS_NewClass) and embedder state (JS_GetOpaque and JS_SetOpaque.)

Checkpointing and suspend/resume won't work when executing JS (it's executed on the C stack) but that's no different from V8.

[bnoordhuis]

Quick prototyping indicates there's indeed a long tail of object types that won't serialize, like promises, for example.

C functions exposed as JS functions don't serialize. Probably needs some kind of registry-based approach (serialize: map function pointer to ID, deserialize: map ID to function pointer.)

Open question: how to deal with monkey-patched built-ins. E.g. what if I set Math.PI = 3?