allow set directory for heapsnapshot

[cheskayang]

Is your feature request related to a problem? Please describe.
Please describe the problem you are trying to solve.
the --heapsnapshot-signal and --heap snapshot-near-heap-limit is very handy when dealing with memory issues.
if we can add a flag to allow setting the directory where the heap snapshop is written to, it would give a lot of flexibility.

Describe the solution you'd like
Please describe the desired behavior.
allow set the directory where heap snapshot is written to

Describe alternatives you've considered
Please describe alternative solutions or features you have considered.

[gireeshpunathil]

looks like a valid requirement to me!

[himadriganguly]

I would like to pick this up. Can you please assign this to me?

[gireeshpunathil]

@himadriganguly - no need of assignment, the above note is sufficient. go ahead!

[himadriganguly]

Ok. Thank you.

[simllll]

Is this possible already somehow?

[tholcman]

Hi,
for those who haven't found it yet:

node --version
v16.15.0

and

--heapsnapshot-near-heap-limit=1 --diagnostic-dir=/diags

works for us, but I guess the same override as with --cpu-prof-dir and others should be possible.

[sergeyampo]

If I run node with next flags:

node --heapsnapshot-near-heap-limit=2 --heapsnapshot-signal=SIGUSR2 --diagnostic-dir=/diags concurrent.mjs

and try to send a SIGUSR2 signal to a running process I'll notice that .heapsnapshot file will be generated in working directory and --diagnostic-dir flag will be ignored.
Suddenly, --heapsnapshot-near-heap-limit flag generates a snapshot file in --diagnostic-dir directory.
I think it's a bug and it's reproduced on LTS node version 16.18.0 and on 18.10.0 too.

[bnoordhuis]

Do you have the heapdump module installed? If find node_modules -name \*heapdump* prints anything, the answer is 'yes'.

[mhdawson]

@bnoordhuis I think their comment is about the heapsnapshot functionality built into node core versus the external module?

[bnoordhuis]

If you load node-heapdump, it overrides node's own SIGUSR2 handler. You'll get snapshots but not in the directory you specified.

[mhdawson]

@bnoordhuis got it thanks.

[bnoordhuis]

Original feature request has been implemented and no follow-up from @sergeyampo so I'm going to go ahead and close this as done.

[thefloweringash]

If I run node with next flags:

node --heapsnapshot-near-heap-limit=2 --heapsnapshot-signal=SIGUSR2 --diagnostic-dir=/diags concurrent.mjs

and try to send a SIGUSR2 signal to a running process I'll notice that .heapsnapshot file will be generated in working directory and --diagnostic-dir flag will be ignored. Suddenly, --heapsnapshot-near-heap-limit flag generates a snapshot file in --diagnostic-dir directory. I think it's a bug and it's reproduced on LTS node version 16.18.0 and on 18.10.0 too.

I'm also seeing this behavior. Specifically the handler for the signal does not use the diagnostic directory.

---

Looking at the code, Environment::NearHeapLimitCallback uses diagnostic_dir

node/src/env.cc

Lines 1830 to 1842 in 38e6ac7

	std::string dir = env->options()->diagnostic_dir;
	if (dir.empty()) {
	dir = env->GetCwd();
	}
	DiagnosticFilename name(env, "Heap", "heapsnapshot");
	std::string filename = dir + kPathSeparator + (*name);
	Debug(env, DebugCategory::DIAGNOSTICS, "Start generating %s...\n", *name);
	HeapProfiler::HeapSnapshotOptions options;
	options.numerics_mode = HeapProfiler::NumericsMode::kExposeNumericValues;
	options.snapshot_mode = HeapProfiler::HeapSnapshotMode::kExposeInternals;
	heap::WriteSnapshot(env, filename.c_str(), options);

but TriggerHeapSnapshot (without an explicit filename) does not:

node/src/heap_utils.cc

Lines 456 to 457 in 38e6ac7

	DiagnosticFilename name(env, "Heap", "heapsnapshot");
	if (WriteSnapshot(env, *name, options).IsNothing()) return;

[SteffenLanger]

In case anyone else finds this issue and wonders about a solution for @thefloweringash's message: There is a pending pull request by @MrJithil 💪🏼