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1import "server-only";
2
3import os from "node:os";
4
5export type CpuTimes = { busyMs: number; totalMs: number };
6
7/** CPU time spent busy and in total since boot, summed over all cores. */
8export function readCpuTimes(cpus: os.CpuInfo[] = os.cpus()): CpuTimes {
9  let busyMs = 0;
10  let totalMs = 0;
11  for (const { times } of cpus) {
12    const busy = times.user + times.nice + times.sys + times.irq;
13    busyMs += busy;
14    totalMs += busy + times.idle;
15  }
16  return { busyMs, totalMs };
17}
18
19/**
20 * Turns successive readings into a 0-100 load percent, the way `top` does.
21 *
22 * The kernel already keeps these counters, so this replaces
23 * systeminformation's currentLoad(), which runs `cat /proc/stat | grep cpu`
24 * through execSync and freezes the event loop on every metrics snapshot.
25 */
26export function createCpuLoadTracker() {
27  let previous: CpuTimes | null = null;
28
29  return function update(now: CpuTimes): number | null {
30    const before = previous;
31    previous = now;
32    if (!before) return null;
33
34    const totalMs = now.totalMs - before.totalMs;
35    const busyMs = now.busyMs - before.busyMs;
36    // No time passed, or the counters went backwards: no load this round.
37    if (totalMs <= 0 || busyMs < 0) return null;
38
39    return (busyMs / totalMs) * 100;
40  };
41}
42