Heap snapshot does not seem to work anymore on 1.11 (in chrome profile loader)

[KristofferC]

julia> using Profile

julia> Profile.take_heap_snapshot("1.11.heapsnapshot")
"1.11.heapsnapshot"

Trying to load this in Chrome leads to

An error occurred when a call to method 'buildSnapshot' was requested
TypeError: Cannot read properties of undefined (reading '1')
    at F.name (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:8216)
    at F.rawName (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:38825)
    at F.name (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:39038)
    at F.isDocumentDOMTreesRoot (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:40431)
    at b.isUserRoot (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:35720)
    at b.calculateDistances (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:18912)
    at b.calculateDistances (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:35160)
    at b.initialize (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:14141)
    at new b (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:33684)
    at A.buildSnapshot (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:43578)

On 1.10 the same procedure works fine.

[IanButterworth]

Does the snapshot load in vscode's viewer?

[KristofferC]

In VSCode I can load the 1.11 snapshot but not the 1.10 one...

[IanButterworth]

Yeah these aren't backported to 1.10 yet
#53833
#53984

[nsajko]

AFAIK the VS Code heap snapshot viewer doesn't allow diffing two heap snapshots, unlike the Chromium Dev Tools? So I guess there's currently no way to diff heap snapshots 🫤.

[IanButterworth]

Any help figuring out why would be appreciated. They seem to expect different metadata. See the PRs that have changed it

[IanButterworth]

Trying to get to the bottom of this.

Supposedly this is a valid V8 structure

{
  "snapshot": {
    "title": "Heap Snapshot",
    "uid": 1,
    "meta": {
      "node_fields": ["type", "name", "id", "self_size", "edge_count"],
      "node_types": [
        ["object", "closure", "regexp", "string", "number", "native", "synthetic", "concatenated string", "sliced string"],
        "string",
        "number",
        "number",
        "number"
      ],
      "edge_fields": ["type", "name_or_index", "to_node"],
      "edge_types": [
        ["context", "element", "property", "internal", "hidden", "shortcut", "weak"],
        "string_or_number",
        "node"
      ]
    },
    "node_count": 1000,
    "edge_count": 5000
  },
  "strings": [
    "",
    "(root)",
    "Object",
    "Array",
    "foo",
    "bar",
    /* ... other strings ... */
  ],
  "nodes": [
    0, 1, 2, 3, 4, /* ... node data ... */
  ],
  "edges": [
    0, 1, 2, /* ... edge data ... */
  ],
  /* ... other sections ... */
}

A julia example I just collected

{
  "snapshot": {
    "meta": {
      "node_fields": ["type", "name", "id", "self_size", "edge_count", "trace_node_id", "detachedness"],
      "node_types": [
        ["synthetic", "jl_task_t", "jl_module_t", "jl_array_t", "object", "jl_datatype_t", "String", "jl_svec_t", "jl_sym_t"],
        "string",
        "number",
        "number",
        "number",
        "number",
        "number"
      ],
      "edge_fields": ["type", "name_or_index", "to_node"],
      "edge_types": [
        ["internal", "element", "hidden", "property", "binding"],
        "string_or_number",
        "from_node"
      ],
      "trace_function_info_fields": ["function_id", "name", "script_name", "script_id", "line", "column"],
      "trace_node_fields": ["id", "function_info_index", "count", "size", "children"],
      "sample_fields": ["timestamp_us", "last_assigned_id"],
      "location_fields": ["object_index", "script_id", "line", "column"]
    },
    "node_count": 1759206,
    "edge_count": 5447107,
    "trace_function_count": 0
  },
  "trace_function_infos": [],
  "trace_tree": [],
  "samples": [],
  "locations": [],
  "nodes": [
    0, 0, 0, 0, 4, 0, 0,
    0, 1, 1, 0, 6, 0, 0,
...
  "edges":[
    0,1,7,
    0,2,14,
...
  "strings":[
    "",
    "GC roots",
    ...
}

#53833 which fixed opening in VSCode's viewer, and likely broke chrome devtools made these changes

References:
https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/memory-problems/heap-snapshot-schema#schema-of-the-heapsnapshot-data
https://v8docs.nodesource.com/node-0.8/d8/deb/classv8_1_1_heap_snapshot.html#a159532596beaf59473bf3189703c39a1

[IanButterworth]

The problem appears to be the inclusion of

  "sample_fields":["timestamp_us","last_assigned_id"],
  "location_fields":["object_index","script_id","line","column"]

without it vscode cannot load the heapsnapshot, but chrome devtools can.
with it chrome devtools cannot, but vscode can.

[IanButterworth]

Dev tools parsing for those fields (which fails if they are there, but the line numbers don't correspond to here)
https://github.com/ChromeDevTools/devtools-frontend/blob/75970e0fc2a9be009fa4d946cedc0e0018c16a88/front_end/entrypoints/heap_snapshot_worker/HeapSnapshotLoader.ts#L241-L251

vscode
https://github.com/microsoft/vscode-v8-heap-tools/blob/c5b34396392397925ecbb4ecb904a27a2754f2c1/v8-heap-parser/src/decoder.rs#L48-L50

It'd be helpful to find the exact files & lines these are coming from in devtools, but I guess these js files were minified

TypeError: Cannot read properties of undefined (reading 'length')
    at new O (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:13338)
    at new A (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:39902)
    at R.buildSnapshot (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:50296)
    at HeapSnapshotWorkerDispatcher.dispatchMessage (devtools://devtools/bundled/devtools-frontend/front_end/entrypoints/heap_snapshot_worker/heap_snapshot_worker.js:1:54089)

[IanButterworth]

The error above is to this (in an unminified version of heap_snapshot_worker,js) https://gist.github.com/IanButterworth/9fb742180ee6e682e04d34819fd9d500#file-heap_snapshot_worker-js-L693

So somehow the inclusion of

  "sample_fields":["timestamp_us","last_assigned_id"],
  "location_fields":["object_index","script_id","line","column"]

is preventing strings from being populated.

---

It's this raw line https://github.com/ChromeDevTools/devtools-frontend/blob/2709fa744749f851721829cc218698729f74bd24/front_end/entrypoints/heap_snapshot_worker/HeapSnapshot.ts#L828

[gbaraldi]

https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/memory-problems/heap-snapshot-schema not sure if this is helpful but I always drop it.