support taking HeapSnapshots

[bartlomieju]

To figure out performance problems with deno_tcp.ts (which are GC problems) we need to inspect what's going on on V8 heap.

This is partially related to #205 but can be implemented independently and used without full inspector support.

There's node-heapdump which implements that functionality fo node.

Grepping through node-heapdump/heapdump.cc it seems that APIs that we should port are:

• Isolate::GetHeapProfiler
• HeapProfiler::TakeHeapSnapshot
• HeapSnapshot::Serialize

CC @bnoordhuis for expert advice on the subject

[bnoordhuis]

I can write bindings, that shouldn't be too complicated, but the question is where to send the data chunks to.

node-heapdump writes them out to disk to avoid having to round-trip through JS land because it's easy to hit out-of-memory conditions that way.

[bartlomieju]

I can write bindings, that shouldn't be too complicated, but the question is where to send the data chunks to.

node-heapdump writes them out to disk to avoid having to round-trip through JS land because it's easy to hit out-of-memory conditions that way.

That'd be awesome thanks! My direct need for this feature is to take some dumps of deno_tcp.ts heap; I haven't put much thought how to call that API, but I guess I could just directly bind it to global object (globalThis.takeHeapSnapshot()) and write out to disk - but that would be done in deno_core

[bnoordhuis]

I'll open a PR here tomorrow.

[bartlomieju]

Done in #302