Introduce a ZED_MEASUREMENTS env var and use it to measure frame time

crates/util/src/util.rs

@@ -7,19 +7,21 @@ pub mod paths;
 #[cfg(any(test, feature = "test-support"))]
 pub mod test;
 
+pub use backtrace::Backtrace;
+use futures::Future;
+use lazy_static::lazy_static;
+use rand::{seq::SliceRandom, Rng};
 use std::{
     borrow::Cow,
     cmp::{self, Ordering},
+    env,
     ops::{AddAssign, Range, RangeInclusive},
     panic::Location,
     pin::Pin,
     task::{Context, Poll},
+    time::Instant,
 };
 
-pub use backtrace::Backtrace;
-use futures::Future;
-use rand::{seq::SliceRandom, Rng};
-
 pub use take_until::*;
 
 #[macro_export]
@@ -133,6 +135,24 @@ pub fn merge_non_null_json_value_into(source: serde_json::Value, target: &mut se
     }
 }
 
+pub fn measure<R>(label: &str, f: impl FnOnce() -> R) -> R {
+    lazy_static! {
+        pub static ref ZED_MEASUREMENTS: bool = env::var("ZED_MEASUREMENTS")
+            .map(|measurements| measurements == "1" || measurements == "true")
+            .unwrap_or(false);
+    }
+
+    if *ZED_MEASUREMENTS {
+        let start = Instant::now();
+        let result = f();
+        let elapsed = start.elapsed();
+        eprintln!("{}: {:?}", label, elapsed);
+        result
+    } else {
+        f()
+    }
+}
+
 pub trait ResultExt<E> {
     type Ok;