Add getrusage suite to sys.

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/sys.rs

@@ -1,10 +1,11 @@
 pub mod compute;
 pub mod limits;
 pub mod storage;
+pub mod usage;
 
 use std::path::PathBuf;
 
-pub use self::{compute::available_parallelism, limits::*};
+pub use self::{compute::available_parallelism, limits::*, usage::*};
 use crate::{Result, at};
 
 /// Return a possibly corrected std::env::current_exe() even if the path is

src/core/utils/sys/usage.rs

@@ -0,0 +1,25 @@
+use nix::sys::resource::Usage;
+#[cfg(unix)]
+use nix::sys::resource::{UsageWho, getrusage};
+
+use crate::Result;
+
+#[cfg(unix)]
+pub fn usage() -> Result<Usage> { getrusage(UsageWho::RUSAGE_SELF).map_err(Into::into) }
+
+#[cfg(not(unix))]
+pub fn usage() -> Result<Usage> { Ok(Usage::default()) }
+
+#[cfg(any(
+	target_os = "linux",
+	target_os = "freebsd",
+	target_os = "openbsd"
+))]
+pub fn thread_usage() -> Result<Usage> { getrusage(UsageWho::RUSAGE_THREAD).map_err(Into::into) }
+
+#[cfg(not(any(
+	target_os = "linux",
+	target_os = "freebsd",
+	target_os = "openbsd"
+)))]
+pub fn thread_usage() -> Result<Usage> { Ok(Usage::default()) }