runtime metrics blocking threads miscount

[conradludgate]

Version

cargo tree | grep tokio

measured-tokio v0.0.21 (/Users/conrad/Documents/code/better-metrics/tokio)
└── tokio v1.37.0
└── tokio v1.37.0 (*)

Platform

Darwin Conrads-MacBook-Pro.local 23.4.0 Darwin Kernel Version 23.4.0: Fri Mar 15 00:12:49 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6020 arm64

Description
RuntimeMetrics::num_blocking_threads() double counts the worker_threads().

I tried this code:

let rt = tokio::runtime::Builder::new_multi_thread()
    .worker_threads(4)
    .build()
    .unwrap();
let metrics = rt.metrics();
let workers = metrics.num_workers();
let blocking = metrics.num_blocking_threads();
println!("{workers} - {blocking}");

I expected to see this happen: "4 - 0"

Instead, this happened: "4 - 4"

Tokio worker threads are spawned inside of blocking threads as an implementation detail, so the blocking thread count is artificially inflated.