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fix(core): seed the V8 RNG and string hashes in walltime mode #105

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fix(core): seed the V8 RNG and string hashes in walltime mode #105

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17 changes: 12 additions & 5 deletions packages/core/src/introspection.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,15 @@ const CUSTOM_INTROSPECTION_EXIT_CODE = 0;

const V8_LOG_FILENAME_PATTERN = "codspeed-v8-%p.log";

// Fixed seeds so Math.random() and hash table layout match on every run
const getSeedFlags = (nodeVersionMajor: number) => {
const flags = ["--hash-seed=1", "--random-seed=1"];
if (nodeVersionMajor < 18) {
flags.push("--no-randomize-hashes");
}
return flags;
};

export const getV8Flags = () => {
const nodeVersionMajor = parseInt(process.version.slice(1).split(".")[0]);
const instrumentMode = getInstrumentMode();
Expand All @@ -17,8 +26,7 @@ export const getV8Flags = () => {
case "analysis": {
flags.push(
...[
"--hash-seed=1",
"--random-seed=1",
...getSeedFlags(nodeVersionMajor),
"--no-opt",
"--always-sparkplug",
"--predictable",
Expand All @@ -28,9 +36,6 @@ export const getV8Flags = () => {
"--max-old-space-size=4096",
],
);
if (nodeVersionMajor < 18) {
flags.push("--no-randomize-hashes");
}
if (nodeVersionMajor < 20) {
flags.push("--no-scavenge-task");
} else {
Expand All @@ -48,6 +53,8 @@ export const getV8Flags = () => {
}

case "walltime": {
flags.push(...getSeedFlags(nodeVersionMajor));

// Emit the V8 jitdump
flags.push("--perf-prof");

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