Auto merge of rust-lang#97911 - dtolnay:numcpu, r=Mark-Simulacrum

Revert "remove num_cpus dependency" in rustc and update cargo

Fixes rust-lang#97549. This PR reverts rust-lang#94524 and does a Cargo update to pull in rust-lang/cargo#10737.

Rust 1.61.0 has a regression in which it misidentifies the number of available CPUs in some environments, leading to enormously increased memory usage and failing builds. In between Rust 1.60 and 1.61 both rustc and cargo replaced some uses of `num_cpus` with `available_parallelism`, which eliminated support for cgroupv1, still apparently in common use. This PR switches both rustc and cargo back to using `num_cpus` in order to support environments where the available parallelism is controlled by cgroupv1. Both can use `available_parallism` again once it handles cgroupv1 (if ever).

I have confirmed that the rustc part of this PR fixes the memory usage regression in my non-Cargo environment, and others have confirmed in rust-lang#97549 that the Cargo regression was at fault for the memory usage regression in their environments.

Cargo.lock

@@ -218,6 +218,7 @@ dependencies = [
  "getopts",
  "ignore",
  "libc",
+ "num_cpus",
  "once_cell",
  "opener",
  "pretty_assertions",
@@ -247,6 +248,7 @@ dependencies = [
  "anyhow",
  "flate2",
  "hex 0.4.2",
+ "num_cpus",
  "rayon",
  "serde",
  "serde_json",
@@ -346,6 +348,7 @@ dependencies = [
  "libgit2-sys",
  "log",
  "memchr",
+ "num_cpus",
  "opener",
  "openssl",
  "os_info",
@@ -4338,6 +4341,7 @@ name = "rustc_session"
 version = "0.0.0"
 dependencies = [
  "getopts",
+ "num_cpus",
  "rustc_ast",
  "rustc_data_structures",
  "rustc_errors",

compiler/rustc_session/Cargo.toml

@@ -15,5 +15,6 @@ 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

@@ -578,7 +578,7 @@ mod parse {
     crate fn parse_threads(slot: &mut usize, v: Option<&str>) -> bool {
         match v.and_then(|s| s.parse().ok()) {
             Some(0) => {
-                *slot = std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get);
+                *slot = ::num_cpus::get();
                 true
             }
             Some(i) => {

src/bootstrap/Cargo.toml

@@ -37,6 +37,7 @@ test = false
 [dependencies]
 cmake = "0.1.38"
 filetime = "0.2"
+num_cpus = "1.0"
 getopts = "0.2.19"
 cc = "1.0.69"
 libc = "0.2"

src/bootstrap/config.rs

@@ -1345,7 +1345,7 @@ fn set<T>(field: &mut T, val: Option<T>) {
 
 fn threads_from_config(v: u32) -> u32 {
     match v {
-        0 => std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get) as u32,
+        0 => num_cpus::get() as u32,
         n => n,
     }
 }

src/bootstrap/flags.rs

@@ -210,7 +210,7 @@ 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)",
-            std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get)
+            num_cpus::get()
         );
         opts.optopt("j", "jobs", &j_msg, "JOBS");
         opts.optflag("h", "help", "print this help message");

src/bootstrap/lib.rs

@@ -993,9 +993,7 @@ 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(|| {
-            std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get) as u32
-        })
+        self.config.jobs.unwrap_or_else(|| num_cpus::get() as u32)
     }
 
     fn debuginfo_map_to(&self, which: GitRepo) -> Option<String> {

src/tools/build-manifest/Cargo.toml

@@ -13,3 +13,4 @@ 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 {
-        std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get)
+        num_cpus::get()
     };
     rayon::ThreadPoolBuilder::new()
         .num_threads(num_threads)