Add a sched_getcpu wrapper

Author: Jonas Schievink

CHANGELOG.md

@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Added `sched_getcpu` on platforms that support it.
+  ([#1825](https://github.com/nix-rust/nix/pull/1825))
 - Added `sched_getaffinity` and `sched_setaffinity` on FreeBSD.
   ([#1804](https://github.com/nix-rust/nix/pull/1804))
 - Added `line_discipline` field to `Termios` on Linux, Android and Haiku

src/sched.rs

@@ -290,6 +290,13 @@ mod sched_affinity {
 
         Errno::result(res).and(Ok(cpuset))
     }
+
+    /// Determines the CPU on which the calling thread is running.
+    pub fn sched_getcpu() -> Result<usize> {
+        let res = unsafe { libc::sched_getcpu() };
+
+        Errno::result(res).map(|int| int as usize)
+    }
 }
 
 /// Explicitly yield the processor to other threads.

test/test_sched.rs

@@ -1,4 +1,4 @@
-use nix::sched::{sched_getaffinity, sched_setaffinity, CpuSet};
+use nix::sched::{sched_getaffinity, sched_getcpu, sched_setaffinity, CpuSet};
 use nix::unistd::Pid;
 
 #[test]
@@ -30,6 +30,10 @@ fn test_sched_affinity() {
         )
     }
 
+    // Now check that we're also currently running on the CPU in question.
+    let cur_cpu = sched_getcpu().unwrap();
+    assert_eq!(cur_cpu, last_valid_cpu);
+
     // Finally, reset the initial CPU set
     sched_setaffinity(Pid::from_raw(0), &initial_affinity).unwrap();
 }