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fix: avoid forced GC during allocation profile collection #435

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fix: avoid forced GC during allocation profile collection #435

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1 change: 0 additions & 1 deletion bindings/profilers/heap.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,6 @@ NAN_METHOD(HeapProfiler::StartSamplingHeapProfiler) {
#if NODE_MAJOR_VERSION >= 26
if (allocations) {
flags = static_cast<v8::HeapProfiler::SamplingFlags>(
v8::HeapProfiler::kSamplingForceGC |
v8::HeapProfiler::kSamplingIncludeObjectsCollectedByMajorGC |
v8::HeapProfiler::kSamplingIncludeObjectsCollectedByMinorGC);
}
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5 changes: 2 additions & 3 deletions ts/src/heap-profiler.ts
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Expand Up @@ -204,9 +204,8 @@ export function profileV2(
* @param intervalBytes - average number of bytes between samples.
* @param stackDepth - maximum stack depth for samples collected.
* @param allocations - include total allocation samples in the profile.
* When true, each call to `profile()` forces a full GC (via
* v8::HeapProfiler::kSamplingForceGC) to classify sampled objects as
* live/dead, which adds a measurable pause. Requires Node.js >= 26.
* Retains samples of objects collected by GC. Liveness reflects the most
* recent GC; collecting a profile does not force one. Requires Node.js >= 26.
*/
export function start(
intervalBytes: number,
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27 changes: 26 additions & 1 deletion ts/test/test-heap-profiler.ts
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Expand Up @@ -23,7 +23,7 @@ import {
AllocationProfileNodeWithStats,
LabelSet,
} from '../src/v8-types';
import {fork} from 'child_process';
import {execFileSync, fork} from 'child_process';
import path from 'path';
import fs from 'fs';

Expand Down Expand Up @@ -330,6 +330,31 @@ describe('HeapProfiler', () => {
});
});

it('should collect allocation profiles without forcing GC', function () {
this.timeout(30000);
if (Number(process.versions.node.split('.')[0]) < 26) this.skip();

const output = execFileSync(
process.execPath,
[
'--trace-gc',
'-e',
`
const heap = require(${JSON.stringify(require.resolve('../src/heap-profiler'))});
heap.start(512 * 1024, 64, true);
global.retained = Array.from({length: 200000}, (_, i) => ({i}));
console.time('10 allocation profiles');
for (let i = 0; i < 10; i++) heap.profile();
console.timeEnd('10 allocation profiles');
heap.stop();
`,
],
{encoding: 'utf8', timeout: 25000},
);
console.log(output.trim());
assert.doesNotMatch(output, /sampling profiler/);
});

describe('foreign heap sampler', () => {
// Regression test: V8's sampling heap profiler can be enabled by something
// other than pprof (inspector, DevTools, another agent). getAllocationProfile
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