lib,src,doc: add --heapsnapshot-signal CLI flag

This flag allows heap snapshots to be captured without
modifying application code.

PR-URL: #27133
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/cli.md

@@ -230,6 +230,14 @@ https://github.com/tc39/ecma262/pull/1320.
 
 Both of the above may change in future updates, which will be breaking changes.
 
+### `--heapsnapshot-signal=signal`
+<!-- YAML
+added: REPLACEME
+-->
+
+Generates a heap snapshot each time the process receives the specified signal.
+`signal` must be a valid signal name. Disabled by default.
+
 ### `--http-parser=library`
 <!-- YAML
 added: v11.4.0
@@ -765,6 +773,7 @@ Node.js options that are allowed are:
 - `--experimental-vm-modules`
 - `--force-fips`
 - `--frozen-intrinsics`
+- `--heapsnapshot-signal`
 - `--icu-data-dir`
 - `--inspect`
 - `--inspect-brk`

doc/node.1

@@ -156,6 +156,9 @@ Same requirements as
 .It Fl -frozen-intrinsics
 Enable experimental frozen intrinsics support.
 .
+.It Fl -heapsnapshot-signal Ns = Ns Ar signal
+Generate heap snapshot on specified signal.
+.
 .It Fl -http-parser Ns = Ns Ar library
 Chooses an HTTP parser library. Available values are
 .Sy llhttp

lib/internal/bootstrap/pre_execution.js

@@ -29,6 +29,8 @@ function prepareMainThreadExecution(expandArgv1 = false) {
   initializeReport();
   initializeReportSignalHandlers();  // Main-thread-only.
 
+  initializeHeapSnapshotSignalHandlers();
+
   // If the process is spawned with env NODE_CHANNEL_FD, it's probably
   // spawned by our child_process module, then initialize IPC.
   // This attaches some internal event listeners and creates:
@@ -166,6 +168,20 @@ function initializeReportSignalHandlers() {
   addSignalHandler();
 }
 
+function initializeHeapSnapshotSignalHandlers() {
+  const signal = getOptionValue('--heapsnapshot-signal');
+
+  if (!signal)
+    return;
+
+  require('internal/validators').validateSignalName(signal);
+  const { writeHeapSnapshot } = require('v8');
+
+  process.on(signal, () => {
+    writeHeapSnapshot();
+  });
+}
+
 function setupTraceCategoryState() {
   const { isTraceCategoryEnabled } = internalBinding('trace_events');
   const { toggleTraceCategoryState } = require('internal/process/per_thread');

src/node_options.cc

@@ -273,6 +273,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "experimental frozen intrinsics support",
             &EnvironmentOptions::frozen_intrinsics,
             kAllowedInEnvironment);
+  AddOption("--heapsnapshot-signal",
+            "Generate heap snapshot on specified signal",
+            &EnvironmentOptions::heap_snapshot_signal,
+            kAllowedInEnvironment);
   AddOption("--http-parser",
             "Select which HTTP parser to use; either 'legacy' or 'llhttp' "
             "(default: llhttp).",

src/node_options.h

@@ -100,6 +100,7 @@ class EnvironmentOptions : public Options {
   bool experimental_vm_modules = false;
   bool expose_internals = false;
   bool frozen_intrinsics = false;
+  std::string heap_snapshot_signal;
   std::string http_parser = "llhttp";
   bool no_deprecation = false;
   bool no_force_async_hooks_checks = false;

test/sequential/test-heapdump-flag.js

@@ -0,0 +1,41 @@
+'use strict';
+const common = require('../common');
+
+if (common.isWindows)
+  common.skip('test not supported on Windows');
+
+const assert = require('assert');
+
+if (process.argv[2] === 'child') {
+  const fs = require('fs');
+
+  assert.strictEqual(process.listenerCount('SIGUSR2'), 1);
+  process.kill(process.pid, 'SIGUSR2');
+  process.kill(process.pid, 'SIGUSR2');
+
+  // Asynchronously wait for the snapshot. Use an async loop to be a bit more
+  // robust in case platform or machine differences throw off the timing.
+  (function validate() {
+    const files = fs.readdirSync(process.cwd());
+
+    if (files.length === 0)
+      return setImmediate(validate);
+
+    assert.strictEqual(files.length, 2);
+
+    for (let i = 0; i < files.length; i++) {
+      assert(/^Heap\..+\.heapsnapshot$/.test(files[i]));
+      JSON.parse(fs.readFileSync(files[i]));
+    }
+  })();
+} else {
+  const { spawnSync } = require('child_process');
+  const tmpdir = require('../common/tmpdir');
+
+  tmpdir.refresh();
+  const args = ['--heapsnapshot-signal', 'SIGUSR2', __filename, 'child'];
+  const child = spawnSync(process.execPath, args, { cwd: tmpdir.path });
+
+  assert.strictEqual(child.status, 0);
+  assert.strictEqual(child.signal, null);
+}