Revert rust-lang#10427: switch from num_cpus

This reverts commit 6d11f9e, reversing
changes made to c5cdd25.

Cargo.toml

@@ -44,6 +44,7 @@ libc = "0.2"
 log = "0.4.6"
 libgit2-sys = "0.13.2"
 memchr = "2.1.3"
+num_cpus = "1.0"
 opener = "0.5"
 os_info = "3.0.7"
 pathdiff = "0.2"

src/cargo/core/compiler/build_config.rs

@@ -1,12 +1,11 @@
 use crate::core::compiler::CompileKind;
 use crate::util::interning::InternedString;
 use crate::util::{CargoResult, Config, RustfixDiagnosticServer};
-use anyhow::{bail, Context as _};
+use anyhow::bail;
 use cargo_util::ProcessBuilder;
 use serde::ser;
 use std::cell::RefCell;
 use std::path::PathBuf;
-use std::thread::available_parallelism;
 
 /// Configuration information for a rustc build.
 #[derive(Debug)]
@@ -74,12 +73,7 @@ impl BuildConfig {
                  its environment, ignoring the `-j` parameter",
             )?;
         }
-        let jobs = match jobs.or(cfg.jobs) {
-            Some(j) => j,
-            None => available_parallelism()
-                .context("failed to determine the amount of parallelism available")?
-                .get() as u32,
-        };
+        let jobs = jobs.or(cfg.jobs).unwrap_or(::num_cpus::get() as u32);
         if jobs == 0 {
             anyhow::bail!("jobs may not be 0");
         }

src/cargo/core/compiler/timings.rs

@@ -13,7 +13,6 @@ use anyhow::Context as _;
 use cargo_util::paths;
 use std::collections::HashMap;
 use std::io::{BufWriter, Write};
-use std::thread::available_parallelism;
 use std::time::{Duration, Instant, SystemTime};
 
 pub struct Timings<'cfg> {
@@ -381,9 +380,6 @@ impl<'cfg> Timings<'cfg> {
         };
         let total_time = format!("{:.1}s{}", duration, time_human);
         let max_concurrency = self.concurrency.iter().map(|c| c.active).max().unwrap();
-        let num_cpus = available_parallelism()
-            .map(|x| x.get().to_string())
-            .unwrap_or_else(|_| "n/a".into());
         let max_rustc_concurrency = self
             .concurrency
             .iter()
@@ -446,7 +442,7 @@ impl<'cfg> Timings<'cfg> {
             self.total_fresh + self.total_dirty,
             max_concurrency,
             bcx.build_config.jobs,
-            num_cpus,
+            num_cpus::get(),
             self.start_str,
             total_time,
             rustc_info,