From 970dccccd15fded78aa8ff6b6c48a15fb140a173 Mon Sep 17 00:00:00 2001
From: roblabla <unfiltered@roblab.la>
Date: Thu, 10 Dec 2020 16:41:18 +0000
Subject: [PATCH] Add usage

---
 heim-cpu/Cargo.toml     |  1 +
 heim-cpu/src/lib.rs     |  2 +
 heim-cpu/src/usage.rs   | 89 +++++++++++++++++++++++++++++++++++++++++
 heim-cpu/tests/smoke.rs |  5 +++
 4 files changed, 97 insertions(+)
 create mode 100644 heim-cpu/src/usage.rs

diff --git a/heim-cpu/Cargo.toml b/heim-cpu/Cargo.toml
index 7eb74d59..aab9677a 100644
--- a/heim-cpu/Cargo.toml
+++ b/heim-cpu/Cargo.toml
@@ -47,6 +47,7 @@ heim-derive = { version = "0.1.0-beta.1", path = "../heim-derive" }
 smol = "~1.2"
 futures = "~0.3"
 version-sync = "0.9"
+futures-timer = "^3.0"
 
 [package.metadata.docs.rs]
 rustdoc-args = ["--cfg", "docsrs"]
diff --git a/heim-cpu/src/lib.rs b/heim-cpu/src/lib.rs
index 8e057c4f..8d05f9dc 100644
--- a/heim-cpu/src/lib.rs
+++ b/heim-cpu/src/lib.rs
@@ -37,8 +37,10 @@ mod count;
 mod freq;
 mod stats;
 mod times;
+mod usage;
 
 pub use self::count::*;
 pub use self::freq::*;
 pub use self::stats::*;
 pub use self::times::*;
+pub use self::usage::*;
diff --git a/heim-cpu/src/usage.rs b/heim-cpu/src/usage.rs
new file mode 100644
index 00000000..efa17d00
--- /dev/null
+++ b/heim-cpu/src/usage.rs
@@ -0,0 +1,89 @@
+use std::ops;
+use std::time::Instant;
+
+use heim_common::prelude::*;
+use heim_common::units::{ratio, time, Ratio};
+
+use super::{logical_count, time, CpuTime};
+
+/// System CPU usage measurement.
+///
+/// See [cpu_usage](./fn.cpu_usage.html) method for details.
+#[derive(Debug, Clone)]
+pub struct CpuUsage {
+    pub(crate) cpu_count: u64,
+    pub(crate) cpu_time: CpuTime,
+    pub(crate) at: Instant,
+}
+
+impl ops::Sub<CpuUsage> for CpuUsage {
+    type Output = Ratio;
+
+    #[allow(clippy::suspicious_arithmetic_impl, clippy::cast_lossless)]
+    fn sub(self, rhs: CpuUsage) -> Self::Output {
+        let delta_proc = (self.cpu_time.user() - rhs.cpu_time.user())
+            + (self.cpu_time.system() - rhs.cpu_time.system());
+        let delta_time = self.at - rhs.at;
+
+        // TODO: Can be replaced with a `delta_time.as_secs_f64()`
+        // as soon as https://github.com/rust-lang/rust/issues/54361 will be stable
+        const NANOS_PER_SEC: u32 = 1_000_000_000;
+        let mut delta_time_secs =
+            (delta_time.as_secs() as f64) + (delta_time.as_nanos() as f64) / (NANOS_PER_SEC as f64);
+
+        // Time should calculated across all the cores available
+        delta_time_secs *= self.cpu_count as f64;
+
+        if delta_time_secs != 0.0 {
+            let overall_cpus_ratio = delta_proc.get::<time::second>() / delta_time_secs;
+            let single_cpu_ratio = overall_cpus_ratio * self.cpu_count as f64;
+
+            Ratio::new::<ratio::ratio>(single_cpu_ratio as f32)
+        } else {
+            Ratio::new::<ratio::ratio>(0.0)
+        }
+    }
+}
+
+/// Returns CPU usage measurement.
+///
+/// Returned [`CpuUsage`] struct represents instantaneous CPU usage and does not represent
+/// any reasonable value by itself.
+/// It is suggested to wait for a while with help of any async timer
+/// (for accuracy recommended delay should be at least 100 ms),
+/// call this method once again and subtract former [`CpuUsage`] from the new one.
+///
+/// Same to any *nix system, calculated CPU usage might exceed 100 %
+/// if the process is running multiple threads on different CPU cores.
+///
+/// ## Example
+///
+/// ```rust
+/// # use std::time::Duration;
+/// # use heim_common::units::ratio;
+/// # use heim_common::prelude::*;
+/// # use heim_cpu::usage;
+/// #
+/// # #[heim_derive::main]
+/// # async fn main() -> Result<()> {
+/// let measurement_1 = usage().await?;
+/// // Or any other async timer at your choice
+/// futures_timer::Delay::new(Duration::from_millis(100)).await;
+/// let measurement_2 = usage().await?;
+///
+/// println!("CPU usage: {} %", (measurement_2 - measurement_1).get::<ratio::percent>());
+/// # Ok(())
+/// # }
+/// ```
+///
+/// [`CpuUsage`]: ./struct.CpuUsage.html
+pub async fn usage() -> Result<CpuUsage> {
+    let (cpu_time, cpu_count) =
+        future::try_join(time(), logical_count().map_err(Into::into)).await?;
+
+    Ok(CpuUsage {
+        cpu_count,
+        cpu_time,
+        at: Instant::now(),
+    })
+}
diff --git a/heim-cpu/tests/smoke.rs b/heim-cpu/tests/smoke.rs
index ac2573f2..ed8edd54 100644
--- a/heim-cpu/tests/smoke.rs
+++ b/heim-cpu/tests/smoke.rs
@@ -130,3 +130,8 @@ async fn smoke_cpu_physical_count() {
         assert!(cpus < 1024); // Some sane value till we will have proper unittests
     }
 }
+
+#[heim_derive::test]
+async fn smoke_cpu_usage() {
+    let _measurement = cpu::usage().await.unwrap();
+}