2 files changed, 74 insertions, 0 deletions

diff --git a/crates/ra_prof/src/lib.rs b/crates/ra_prof/src/lib.rs
index ba5609703..eb50965ae 100644
--- a/crates/ra_prof/src/lib.rs
+++ b/crates/ra_prof/src/lib.rs
@@ -1,5 +1,6 @@
 //! A collection of tools for profiling rust-analyzer.
 
+mod stop_watch;
 mod memory_usage;
 #[cfg(feature = "cpu_profiler")]
 mod google_cpu_profiler;
@@ -11,6 +12,7 @@ use std::cell::RefCell;
 pub use crate::{
     hprof::{init, init_from, profile},
     memory_usage::{Bytes, MemoryUsage},
+    stop_watch::{StopWatch, StopWatchSpan},
 };
 
 /// Prints backtrace to stderr, useful for debugging.
diff --git a/crates/ra_prof/src/stop_watch.rs b/crates/ra_prof/src/stop_watch.rs
new file mode 100644
index 000000000..54bfb0559
--- /dev/null
+++ b/crates/ra_prof/src/stop_watch.rs
@@ -0,0 +1,72 @@
+use crate::MemoryUsage;
+use std::{
+    fmt,
+    time::{Duration, Instant},
+};
+
+pub struct StopWatch {
+    time: Instant,
+    counter: Option<perf_event::Counter>,
+    memory: Option<MemoryUsage>,
+}
+
+pub struct StopWatchSpan {
+    pub time: Duration,
+    pub instructions: Option<u64>,
+    pub memory: Option<MemoryUsage>,
+}
+
+impl StopWatch {
+    pub fn start() -> StopWatch {
+        let mut counter = perf_event::Builder::new().build().ok();
+        if let Some(counter) = &mut counter {
+            let _ = counter.enable();
+        }
+        let time = Instant::now();
+        StopWatch { time, counter, memory: None }
+    }
+    pub fn memory(mut self, yes: bool) -> StopWatch {
+        if yes {
+            self.memory = Some(MemoryUsage::current());
+        }
+        self
+    }
+    pub fn elapsed(&mut self) -> StopWatchSpan {
+        let time = self.time.elapsed();
+        let instructions = self.counter.as_mut().and_then(|it| it.read().ok());
+        let memory = self.memory.map(|it| MemoryUsage::current() - it);
+        StopWatchSpan { time, instructions, memory }
+    }
+}
+
+impl fmt::Display for StopWatchSpan {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:.2?}", self.time)?;
+        if let Some(mut instructions) = self.instructions {
+            let mut prefix = "";
+            if instructions > 10000 {
+                instructions /= 1000;
+                prefix = "k"
+            }
+            if instructions > 10000 {
+                instructions /= 1000;
+                prefix = "m"
+            }
+            write!(f, ", {}{}i", instructions, prefix)?;
+        }
+        if let Some(memory) = self.memory {
+            write!(f, ", {}", memory)?;
+        }
+        Ok(())
+    }
+}
+
+// Unclear if we need this:
+// https://github.com/jimblandy/perf-event/issues/8
+impl Drop for StopWatch {
+    fn drop(&mut self) {
+        if let Some(mut counter) = self.counter.take() {
+            let _ = counter.disable();
+        }
+    }
+}