Rollup merge of #100586 - the8472:available_parallelism_2, r=jyn514

Reland changes replacing num_cpus with available_parallelism

Since #97925 added cgroupv1 support the problem in #97549 which lead to the previous revert should be addressed now.

Cargo has reapplied the replacement too https://github.com/rust-lang/cargo/pull/10969

Reverts 1ae4b258267462da0b1aae1badcf83578153c799 (part of #97911)
Relands #94524

7 files changed, 6 insertions, 7 deletions

diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 664ffa1ddd2..84c06fdce70 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -53,7 +53,6 @@ dependencies = [
  "hex",
  "ignore",
  "libc",
- "num_cpus",
  "once_cell",
  "opener",
  "pretty_assertions",
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index 84f6aaf99c1..2dad41bb18f 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -38,7 +38,6 @@ test = false
 cmake = "0.1.38"
 fd-lock = "3.0.6"
 filetime = "0.2"
-num_cpus = "1.0"
 getopts = "0.2.19"
 cc = "1.0.69"
 libc = "0.2"
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index c4983accc68..203db2d3876 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -1465,7 +1465,7 @@ fn set<T>(field: &mut T, val: Option<T>) {
 
 fn threads_from_config(v: u32) -> u32 {
     match v {
-        0 => num_cpus::get() as u32,
+        0 => std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get) as u32,
         n => n,
     }
 }
diff --git a/src/bootstrap/flags.rs b/src/bootstrap/flags.rs
index 1edb513f0b6..789da748100 100644
--- a/src/bootstrap/flags.rs
+++ b/src/bootstrap/flags.rs
@@ -220,7 +220,7 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`",
         let j_msg = format!(
             "number of jobs to run in parallel; \
              defaults to {} (this host's logical CPU count)",
-            num_cpus::get()
+            std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get)
         );
         opts.optopt("j", "jobs", &j_msg, "JOBS");
         opts.optflag("h", "help", "print this help message");
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index a242243aaaf..dcfa92d1004 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -1008,7 +1008,9 @@ impl Build {
     /// Returns the number of parallel jobs that have been configured for this
     /// build.
     fn jobs(&self) -> u32 {
-        self.config.jobs.unwrap_or_else(|| num_cpus::get() as u32)
+        self.config.jobs.unwrap_or_else(|| {
+            std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get) as u32
+        })
     }
 
     fn debuginfo_map_to(&self, which: GitRepo) -> Option<String> {
diff --git a/src/tools/build-manifest/Cargo.toml b/src/tools/build-manifest/Cargo.toml
index c022d3aa0ac..c437bde5ae6 100644
--- a/src/tools/build-manifest/Cargo.toml
+++ b/src/tools/build-manifest/Cargo.toml
@@ -13,4 +13,3 @@ tar = "0.4.29"
 sha2 = "0.10.1"
 rayon = "1.5.1"
 hex = "0.4.2"
-num_cpus = "1.13.0"
diff --git a/src/tools/build-manifest/src/main.rs b/src/tools/build-manifest/src/main.rs
index efe3f2b618b..1a6760d8c68 100644
--- a/src/tools/build-manifest/src/main.rs
+++ b/src/tools/build-manifest/src/main.rs
@@ -210,7 +210,7 @@ fn main() {
     let num_threads = if let Some(num) = env::var_os("BUILD_MANIFEST_NUM_THREADS") {
         num.to_str().unwrap().parse().expect("invalid number for BUILD_MANIFEST_NUM_THREADS")
     } else {
-        num_cpus::get()
+        std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get)
     };
     rayon::ThreadPoolBuilder::new()
         .num_threads(num_threads)