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

Reland changes replacing num_cpus with available_parallelism

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

Cargo has reapplied the replacement too rust-lang/cargo#10969

Reverts 1ae4b25 (part of rust-lang#97911)
Relands rust-lang#94524

Author: matthiaskrgr

Cargo.lock

@@ -257,7 +257,6 @@ dependencies = [
  "anyhow",
  "flate2",
  "hex 0.4.2",
- "num_cpus",
  "rayon",
  "serde",
  "serde_json",
@@ -4442,7 +4441,6 @@ name = "rustc_session"
 version = "0.0.0"
 dependencies = [
  "getopts",
- "num_cpus",
  "rustc_ast",
  "rustc_data_structures",
  "rustc_errors",

compiler/rustc_session/Cargo.toml

@@ -15,6 +15,5 @@ rustc_serialize = { path = "../rustc_serialize" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_span = { path = "../rustc_span" }
 rustc_fs_util = { path = "../rustc_fs_util" }
-num_cpus = "1.0"
 rustc_ast = { path = "../rustc_ast" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }

compiler/rustc_session/src/options.rs

@@ -582,7 +582,7 @@ mod parse {
     pub(crate) fn parse_threads(slot: &mut usize, v: Option<&str>) -> bool {
         match v.and_then(|s| s.parse().ok()) {
             Some(0) => {
-                *slot = ::num_cpus::get();
+                *slot = std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get);
                 true
             }
             Some(i) => {

src/bootstrap/Cargo.lock

@@ -53,7 +53,6 @@ dependencies = [
  "hex",
  "ignore",
  "libc",
- "num_cpus",
  "once_cell",
  "opener",
  "pretty_assertions",

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"

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,
     }
 }

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");

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> {

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"

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)