From 08f7d9e24f2c91636e71ea996cc08a6453501077 Mon Sep 17 00:00:00 2001
From: Jacob Pratt <jacob@jhpratt.dev>
Date: Sun, 14 Nov 2021 23:14:09 -0500
Subject: [PATCH] Implement Linux, FreeBSD

---
 .github/workflows/build.yaml |  6 +++---
 Cargo.toml                   |  4 +++-
 src/freebsd.rs               | 13 +++++++++++++
 src/imp.rs                   |  7 +++++++
 src/lib.rs                   | 20 +++++++++++++++++++-
 src/linux.rs                 | 10 ++++++++++
 6 files changed, 55 insertions(+), 5 deletions(-)
 create mode 100644 src/freebsd.rs
 create mode 100644 src/imp.rs
 create mode 100644 src/linux.rs

diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 40196ed..2813b39 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -25,7 +25,7 @@ on:
       - .gitignore
 
 jobs:
-  check-other-targets:
+  check:
     name: Type checking (${{ matrix.target.name }})
     runs-on: ubuntu-20.04
     if: ${{ (github.event_name == 'pull_request' && github.event.pull_request.head.repo.fork) || github.event_name == 'push' }}
@@ -49,7 +49,7 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.36
+          toolchain: 1.28
           target: ${{ matrix.target.triple }}
           override: true
 
@@ -58,7 +58,7 @@ jobs:
         with:
           key: ${{ matrix.target.triple }}
 
-      - name: Check feature powerset
+      - name: Type checking
         uses: actions-rs/cargo@v1
         with:
           command: check
diff --git a/Cargo.toml b/Cargo.toml
index e345c66..61f17fc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,6 @@
 name = "num_threads"
 version = "0.1.0"
 authors = ["Jacob Pratt <open-source@jhpratt.dev>"]
-edition = "2018"
 repository = "https://github.com/jhpratt/thread_count"
 categories = ["api-bindings", "hardware-support", "os"]
 license = "MIT OR Apache-2.0"
@@ -14,3 +13,6 @@ all-features = true
 targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
+
+[target.'cfg(target_os = "freebsd")'.dependencies]
+libc = "0.2.107"
diff --git a/src/freebsd.rs b/src/freebsd.rs
new file mode 100644
index 0000000..3ff8f61
--- /dev/null
+++ b/src/freebsd.rs
@@ -0,0 +1,13 @@
+extern crate libc;
+
+use std::num::NonZeroUsize;
+
+extern "C" {
+    fn kinfo_getproc(pid: libc::pid_t) -> *mut libc::kinfo_proc;
+}
+
+pub(crate) fn num_threads() -> Option<NonZeroUsize> {
+    // Safety: `kinfo_getproc` and `getpid` are both thread-safe. All invariants of `as_ref` are
+    // upheld.
+    NonZeroUsize::new(unsafe { kinfo_getproc(libc::getpid()).as_ref() }?.ki_numthreads as usize)
+}
diff --git a/src/imp.rs b/src/imp.rs
new file mode 100644
index 0000000..b12465d
--- /dev/null
+++ b/src/imp.rs
@@ -0,0 +1,7 @@
+//! Fallback if no OS matches.
+
+use std::num::NonZeroUsize;
+
+pub(crate) fn num_threads() -> Option<NonZeroUsize> {
+    None
+}
diff --git a/src/lib.rs b/src/lib.rs
index e989fca..09901af 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1,19 @@
-//! Minimum supported Rust version: 1.36
+//! Minimum supported Rust version: 1.28
+
+use std::num::NonZeroUsize;
+
+#[cfg_attr(target_os = "linux", path = "linux.rs")]
+#[cfg_attr(target_os = "freebsd", path = "freebsd.rs")]
+mod imp;
+
+/// Obtain the number of threads currently part of the active process. Returns `None` if the number
+/// of threads cannot be determined.
+pub fn num_threads() -> Option<NonZeroUsize> {
+    imp::num_threads()
+}
+
+/// Determine if the current process is single-threaded. Returns `None` if the number of threads
+/// cannot be determined.
+pub fn is_single_threaded() -> Option<bool> {
+    num_threads().map(|n| n.get() == 1)
+}
diff --git a/src/linux.rs b/src/linux.rs
new file mode 100644
index 0000000..e110c74
--- /dev/null
+++ b/src/linux.rs
@@ -0,0 +1,10 @@
+use std::fs;
+use std::num::NonZeroUsize;
+
+pub(crate) fn num_threads() -> Option<NonZeroUsize> {
+    fs::read_dir("/proc/self/task")
+        // If we can't read the directory, return `None`.
+        .ok()
+        // The number of files in the directory is the number of threads.
+        .and_then(|tasks| NonZeroUsize::new(tasks.count()))
+}