[metrics] Add H2 Histogram option to improve histogram granularity

Author: rcoh

tokio/src/runtime/builder.rs

@@ -6,6 +6,8 @@ use crate::runtime::TaskMeta;
 use crate::runtime::{blocking, driver, Callback, HistogramBuilder, Runtime, TaskCallback};
 use crate::util::rand::{RngSeed, RngSeedGenerator};
 
+#[cfg(tokio_unstable)]
+use crate::runtime::metrics::HistogramConfiguration;
 use std::fmt;
 use std::io;
 use std::time::Duration;
@@ -1114,8 +1116,29 @@ impl Builder {
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_scale(&mut self, histogram_scale: crate::runtime::HistogramScale) -> &mut Self {
-            self.metrics_poll_count_histogram.scale = histogram_scale;
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.scale = histogram_scale);
+            self
+        }
+
+        /// Configure the poll_count histogram
+        ///
+        /// # Examples
+        /// Configure the default `LogHistogram`:
+        /// ```
+        /// use tokio::runtime;
+        /// use std::time::Duration;
+        /// use tokio::runtime::{HistogramConfiguration, LogHistogram};
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .enable_metrics_poll_count_histogram()
+        ///     .metrics_poll_count_histogram_configuration(HistogramConfiguration::log(LogHistogram::default()))
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        pub fn metrics_poll_count_histogram_configuration(&mut self, configuration: HistogramConfiguration) -> &mut Self {
+            self.metrics_poll_count_histogram.histogram_type = configuration.inner;
             self
         }
 
@@ -1145,13 +1168,15 @@ impl Builder {
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_resolution(&mut self, resolution: Duration) -> &mut Self {
             assert!(resolution > Duration::from_secs(0));
             // Sanity check the argument and also make the cast below safe.
             assert!(resolution <= Duration::from_secs(1));
 
             let resolution = resolution.as_nanos() as u64;
-            self.metrics_poll_count_histogram.resolution = resolution;
+
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.resolution = resolution);
             self
         }
 
@@ -1176,8 +1201,9 @@ impl Builder {
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use `metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_buckets(&mut self, buckets: usize) -> &mut Self {
-            self.metrics_poll_count_histogram.num_buckets = buckets;
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.num_buckets = buckets);
             self
         }
     }

tokio/src/runtime/metrics/batch.rs

@@ -171,6 +171,6 @@ cfg_rt_multi_thread! {
     }
 }
 
-fn duration_as_u64(dur: Duration) -> u64 {
+pub(crate) fn duration_as_u64(dur: Duration) -> u64 {
     u64::try_from(dur.as_nanos()).unwrap_or(u64::MAX)
 }