Creat Mock Histogram, HistogramBatch and HistogramBuilder. Revert cha…

…nges on histogram.rs and guard it behind unstable flag

tokio/src/runtime/metrics/histogram.rs

@@ -35,34 +35,31 @@ pub(crate) struct HistogramBatch {
     resolution: u64,
 }
 
-/// Whether the histogram used to aggregate a metric uses a linear or
-/// logarithmic scale.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-#[non_exhaustive]
-#[allow(unreachable_pub)]
-pub enum HistogramScale {
-    /// Linear bucket scale
-    Linear,
-
-    /// Logarithmic bucket scale
-    #[allow(dead_code)]
-    Log,
+cfg_unstable! {
+    /// Whether the histogram used to aggregate a metric uses a linear or
+    /// logarithmic scale.
+    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
+    #[non_exhaustive]
+    pub enum HistogramScale {
+        /// Linear bucket scale
+        Linear,
+
+        /// Logarithmic bucket scale
+        Log,
+    }
 }
 
 impl Histogram {
-    #[allow(dead_code)]
     pub(crate) fn num_buckets(&self) -> usize {
         self.buckets.len()
     }
 
     cfg_64bit_metrics! {
-        #[allow(dead_code)]
         pub(crate) fn get(&self, bucket: usize) -> u64 {
             self.buckets[bucket].load(Relaxed)
         }
     }
 
-    #[allow(dead_code)]
     pub(crate) fn bucket_range(&self, bucket: usize) -> Range<u64> {
         match self.scale {
             HistogramScale::Log => Range {

tokio/src/runtime/metrics/mock.rs

@@ -10,3 +10,27 @@ impl SchedulerMetrics {
     /// Increment the number of tasks scheduled externally
     pub(crate) fn inc_remote_schedule_count(&self) {}
 }
+
+#[derive(Debug)]
+pub(crate) struct Histogram {}
+
+pub(crate) struct HistogramBatch {}
+
+#[derive(Debug, Clone, Default)]
+pub(crate) struct HistogramBuilder {}
+
+impl HistogramBuilder {
+    pub(crate) fn build(&self) -> Histogram {
+        Histogram {}
+    }
+}
+
+impl HistogramBatch {
+    pub(crate) fn from_histogram(_histogram: &Histogram) -> HistogramBatch {
+        HistogramBatch {}
+    }
+
+    pub(crate) fn submit(&self, _histogram: &Histogram) {}
+
+    pub(crate) fn measure(&mut self, _value: u64, _count: u64) {}
+}

tokio/src/runtime/metrics/mod.rs

@@ -17,9 +17,6 @@ pub(crate) use worker::WorkerMetrics;
 mod batch;
 pub(crate) use batch::MetricsBatch;
 
-mod histogram;
-pub(crate) use histogram::{Histogram, HistogramBatch, HistogramBuilder};
-
 cfg_unstable_metrics! {
     #[allow(unreachable_pub)] // rust-lang/rust#57411
     pub use histogram::HistogramScale;
@@ -32,10 +29,14 @@ cfg_unstable_metrics! {
         mod io;
         pub(crate) use io::IoDriverMetrics;
     }
+
+    mod histogram;
+    pub(crate) use histogram::{Histogram, HistogramBatch, HistogramBuilder};
 }
 
 cfg_not_unstable_metrics! {
     mod mock;
 
-    pub(crate) use mock::SchedulerMetrics;
+    pub(crate) use mock::{SchedulerMetrics, Histogram, HistogramBatch, HistogramBuilder};
+
 }