perf(ext/headers): use .push loop instead of spread operator

[marcosc90]

This PR slightly improves performance of Header iterator by using .concat instead of spread operator.

This patch

cpu: 13th Gen Intel(R) Core(TM) i9-13900H
runtime: deno 1.36.0 (x86_64-unknown-linux-gnu)

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator       1.49 µs/iter     669,569.7     (1.48 µs … 1.56 µs)    1.5 µs   1.56 µs   1.56 µs

Main

cpu: 13th Gen Intel(R) Core(TM) i9-13900H
runtime: deno 1.36.0 (x86_64-unknown-linux-gnu)

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator       1.62 µs/iter     617,624.9     (1.59 µs … 1.66 µs)   1.63 µs   1.66 µs   1.66 µs

const headers = new Headers({
  "Content-Type": "application/json",
  "Date": "Wed, 09 Aug 2023 11:37:57 GMT",
});

Deno.bench("Headers iterator", () => {
  const i = [...headers];
});

[bartlomieju]

@marcosc90 very nice, how do the results look like if you increase number of headers to 8-10?

[marcosc90]

@bartlomieju it's always faster, here's the bench for 8 headers.

const headers = new Headers({
  "Content-Type": "application/json",
  "Date": "Wed, 09 Aug 2023 11:37:57 GMT",
  "X-Deno": "Deno",
  "Powered-By": "Deno",
  "Content-Encoding": "gzip",
  "Set-Cookie": "__Secure-ID=123; Secure; Domain=example.com",
  "Content-Length": "150",
  "Vary": "Accept-Encoding, Accept, X-Requested-With"
});

This patch

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator      10.59 µs/iter      94,446.5   (9.64 µs … 107.35 µs)  10.39 µs  14.51 µs  49.75 µs

Main

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator      12.03 µs/iter      83,097.9  (10.97 µs … 243.54 µs)  11.76 µs  16.97 µs  53.33 µs

[marcosc90]

@bartlomieju got much better results with the latest push.

2 headers

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator        1.3 µs/iter     771,516.2     (1.27 µs … 1.32 µs)    1.3 µs   1.32 µs   1.32 µs

8 headers

benchmark             time (avg)        iter/s             (min … max)       p75       p99      p995
---------------------------------------------------------------------- -----------------------------
Headers iterator       9.78 µs/iter     102,259.9    (9.13 µs … 97.81 µs)   9.57 µs  12.61 µs   50.1 µ

[lucacasonato]

Fantastic! Thanks