refactor(stats): use shared measurement statistics

crates/irtt-stats/src/core.rs

@@ -1,9 +1,10 @@
 use std::time::Duration;
 
+use measurement_stats::TimeAccumulator;
+
 use crate::ipdv::{IpdvSample, IpdvTracker};
 use crate::loss::loss_stats;
 use crate::normalization::{ReplySample, StatsEvent};
-use crate::time_stats::TimeMetric;
 use crate::{
     EventCounts, EventStatsUpdate, IpdvPairUpdate, IpdvStats, LateReplyMode, OneWayDelayStats,
     PacketCounts, RttStats, SampleMode, ServerProcessingStats, Snapshot,
@@ -15,17 +16,17 @@ pub(crate) const CONTINUOUS_SEQUENCE_LIMIT: usize = 4096;
 pub(crate) struct CoreStats {
     events: EventCounts,
     packets: PacketCounts,
-    send_call: TimeMetric,
-    timer_error: TimeMetric,
-    rtt_primary: TimeMetric,
-    rtt_raw: TimeMetric,
-    rtt_adjusted: TimeMetric,
-    ipdv_round_trip: TimeMetric,
-    ipdv_send: TimeMetric,
-    ipdv_receive: TimeMetric,
-    send_delay: TimeMetric,
-    receive_delay: TimeMetric,
-    server_processing: TimeMetric,
+    send_call: TimeAccumulator,
+    timer_error: TimeAccumulator,
+    rtt_primary: TimeAccumulator,
+    rtt_raw: TimeAccumulator,
+    rtt_adjusted: TimeAccumulator,
+    ipdv_round_trip: TimeAccumulator,
+    ipdv_send: TimeAccumulator,
+    ipdv_receive: TimeAccumulator,
+    send_delay: TimeAccumulator,
+    receive_delay: TimeAccumulator,
+    server_processing: TimeAccumulator,
     ipdv_tracker: IpdvTracker,
     late_replies: LateReplyMode,
 }
@@ -42,20 +43,25 @@ impl CoreStats {
             Some(CONTINUOUS_SEQUENCE_LIMIT)
         };
 
+        let metric = || match sample_mode {
+            SampleMode::Exact => TimeAccumulator::exact_unbounded(),
+            SampleMode::RunningOnly => TimeAccumulator::running(),
+        };
+
         Self {
             events: EventCounts::default(),
             packets: PacketCounts::default(),
-            send_call: TimeMetric::new(retain_exact),
-            timer_error: TimeMetric::new(retain_exact),
-            rtt_primary: TimeMetric::new(retain_exact),
-            rtt_raw: TimeMetric::new(retain_exact),
-            rtt_adjusted: TimeMetric::new(retain_exact),
-            ipdv_round_trip: TimeMetric::new(retain_exact),
-            ipdv_send: TimeMetric::new(retain_exact),
-            ipdv_receive: TimeMetric::new(retain_exact),
-            send_delay: TimeMetric::new(retain_exact),
-            receive_delay: TimeMetric::new(retain_exact),
-            server_processing: TimeMetric::new(retain_exact),
+            send_call: metric(),
+            timer_error: metric(),
+            rtt_primary: metric(),
+            rtt_raw: metric(),
+            rtt_adjusted: metric(),
+            ipdv_round_trip: metric(),
+            ipdv_send: metric(),
+            ipdv_receive: metric(),
+            send_delay: metric(),
+            receive_delay: metric(),
+            server_processing: metric(),
             ipdv_tracker: IpdvTracker::new(sequence_limit),
             late_replies,
         }
@@ -227,8 +233,8 @@ impl CoreStats {
             events: self.events,
             packets,
             loss: loss_stats(packets),
-            send_call: self.send_call.stats(),
-            timer_error: self.timer_error.stats(),
+            send_call: self.send_call.snapshot(),
+            timer_error: self.timer_error.snapshot(),
             rtt: self.rtt_stats(),
             ipdv: self.ipdv_stats(),
             one_way_delay: self.one_way_delay_stats(),
@@ -238,30 +244,30 @@ impl CoreStats {
 
     fn rtt_stats(&self) -> RttStats {
         RttStats {
-            primary: self.rtt_primary.stats(),
-            raw: self.rtt_raw.stats(),
-            adjusted: self.rtt_adjusted.stats(),
+            primary: self.rtt_primary.snapshot(),
+            raw: self.rtt_raw.snapshot(),
+            adjusted: self.rtt_adjusted.snapshot(),
         }
     }
 
     fn ipdv_stats(&self) -> IpdvStats {
         IpdvStats {
-            round_trip: self.ipdv_round_trip.stats(),
-            send: self.ipdv_send.stats(),
-            receive: self.ipdv_receive.stats(),
+            round_trip: self.ipdv_round_trip.snapshot(),
+            send: self.ipdv_send.snapshot(),
+            receive: self.ipdv_receive.snapshot(),
         }
     }
 
     fn one_way_delay_stats(&self) -> OneWayDelayStats {
         OneWayDelayStats {
-            send_delay: self.send_delay.stats(),
-            receive_delay: self.receive_delay.stats(),
+            send_delay: self.send_delay.snapshot(),
+            receive_delay: self.receive_delay.snapshot(),
         }
     }
 
     fn server_processing_stats(&self) -> ServerProcessingStats {
         ServerProcessingStats {
-            processing: self.server_processing.stats(),
+            processing: self.server_processing.snapshot(),
         }
     }
 }

crates/irtt-stats/src/lib.rs

@@ -15,8 +15,9 @@
 //! [`StatsConfig::continuous`] ([`SampleMode::RunningOnly`]) keeps only
 //! running statistics — no exact median — and bounds its adjacent-sequence
 //! IPDV tracking, so memory stays bounded for a long-running or unbounded
-//! session. Rolling snapshots always use running statistics regardless of
-//! this setting.
+//! session. An enabled time-based rolling window has no item cap and is not
+//! hard-bounded; it expires only when new events arrive. Rolling snapshots
+//! always use running statistics regardless of this setting.
 //!
 //! See `examples/` in the repository for a runnable comparison of both modes.
 
@@ -34,13 +35,13 @@ mod loss;
 mod normalization;
 mod retention;
 mod rolling;
-mod time_stats;
 
 use core::CoreStats;
 pub use loss::LossStats;
+#[doc(inline)]
+pub use measurement_stats::TimeStats;
 use normalization::normalize_event;
 use rolling::RollingEvents;
-pub use time_stats::TimeStats;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 /// Configuration for statistics collection.
@@ -54,6 +55,10 @@ pub struct StatsConfig {
     /// and one unique reply event.
     pub rolling_count: Option<usize>,
     /// Time span of recent normalized events retained for time-based rolling snapshots.
+    ///
+    /// This window has no item cap, even in continuous mode. Its memory depends
+    /// on event volume inside the interval. Expiry occurs on insertion, anchored
+    /// at the latest event timestamp, not when a snapshot is read.
     pub rolling_time: Option<Duration>,
     /// Whether matched late replies contribute measurements.
     pub late_replies: LateReplyMode,
@@ -117,7 +122,8 @@ impl StatsConfig {
     ///
     /// Continuous mode uses running statistics, retains no exact samples so no
     /// timing metric reports a median, and bounds adjacent-sequence IPDV
-    /// tracking for long-running sessions.
+    /// tracking for long-running sessions. An explicitly enabled `rolling_time`
+    /// window is not hard-bounded; use `rolling_count` for bounded event storage.
     ///
     /// # Example
     ///

crates/irtt-stats/src/rolling.rs

@@ -1,14 +1,15 @@
 use std::{collections::VecDeque, time::Duration};
 
+use measurement_stats::CountWindow;
+
 use crate::{
     core::CoreStats, normalization::StatsEvent, LateReplyMode, SampleMode, Snapshot, StatsConfig,
 };
 
 #[derive(Debug, Clone, PartialEq)]
 pub(crate) struct RollingEvents {
-    count_limit: Option<usize>,
     time_limit: Option<Duration>,
-    count_events: Option<VecDeque<StatsEvent>>,
+    count_events: Option<CountWindow<StatsEvent>>,
     time_events: Option<VecDeque<StatsEvent>>,
     late_replies: LateReplyMode,
 }
@@ -16,20 +17,16 @@ pub(crate) struct RollingEvents {
 impl RollingEvents {
     pub(crate) fn new(config: StatsConfig) -> Self {
         Self {
-            count_limit: config.rolling_count,
             time_limit: config.rolling_time,
-            count_events: config.rolling_count.map(|_| VecDeque::new()),
+            count_events: config.rolling_count.map(CountWindow::new),
             time_events: config.rolling_time.map(|_| VecDeque::new()),
             late_replies: config.late_replies,
         }
     }
 
     pub(crate) fn push(&mut self, event: StatsEvent) {
-        if let (Some(limit), Some(window)) = (self.count_limit, self.count_events.as_mut()) {
-            window.push_back(event.clone());
-            while window.len() > limit {
-                window.pop_front();
-            }
+        if let Some(window) = self.count_events.as_mut() {
+            window.push(event.clone());
         }
 
         if let (Some(duration), Some(window)) = (self.time_limit, self.time_events.as_mut()) {
@@ -46,19 +43,22 @@ impl RollingEvents {
     pub(crate) fn count_snapshot(&self) -> Option<Snapshot> {
         self.count_events
             .as_ref()
-            .map(|events| snapshot_window(events, self.late_replies))
+            .map(|events| snapshot_window(events.iter(), self.late_replies))
     }
 
     pub(crate) fn time_snapshot(&self) -> Option<Snapshot> {
         self.time_events
             .as_ref()
-            .map(|events| snapshot_window(events, self.late_replies))
+            .map(|events| snapshot_window(events.iter(), self.late_replies))
     }
 }
 
 /// Recompute a window snapshot under the same normalized semantics as the
 /// cumulative collector, including its late-reply measurement policy.
-fn snapshot_window(events: &VecDeque<StatsEvent>, late_replies: LateReplyMode) -> Snapshot {
+fn snapshot_window<'a>(
+    events: impl Iterator<Item = &'a StatsEvent>,
+    late_replies: LateReplyMode,
+) -> Snapshot {
     let mut core = CoreStats::new(SampleMode::RunningOnly, late_replies);
     for event in events {
         core.apply(event.clone());

crates/irtt-stats/src/time_stats.rs

@@ -1,160 +0,0 @@
-#[derive(Debug, Clone, Copy, PartialEq)]
-/// Summary statistics for timing values.
-///
-/// All fields use nanoseconds except `variance_ns2`, which is nanoseconds
-/// squared. Values may represent signed timing quantities such as scheduling
-/// error or one-way delay.
-pub struct TimeStats {
-    /// Number of samples included in this summary.
-    pub count: u64,
-    /// Sum of all samples, in nanoseconds.
-    pub total_ns: i128,
-    /// Smallest sample, in nanoseconds.
-    pub min_ns: Option<i128>,
-    /// Largest sample, in nanoseconds.
-    pub max_ns: Option<i128>,
-    /// Arithmetic mean, in nanoseconds.
-    pub mean_ns: f64,
-    /// Median, in nanoseconds, when exact samples were retained.
-    ///
-    /// This is `None` when the collector was not configured to retain exact
-    /// samples, and also when it was but this metric received none.
-    pub median_ns: Option<f64>,
-    /// Sample variance, in nanoseconds squared.
-    pub variance_ns2: f64,
-}
-
-impl TimeStats {
-    /// Returns the sample standard deviation, in nanoseconds.
-    pub fn stddev_ns(&self) -> f64 {
-        self.variance_ns2.sqrt()
-    }
-
-    /// Returns whether this summary contains no samples.
-    pub fn is_empty(&self) -> bool {
-        self.count == 0
-    }
-}
-
-#[derive(Debug, Clone, PartialEq)]
-pub(crate) struct TimeMetric {
-    running: RunningStats,
-    samples: Option<Vec<i128>>,
-}
-
-impl TimeMetric {
-    pub(crate) fn new(retain_samples: bool) -> Self {
-        Self {
-            running: RunningStats::default(),
-            samples: retain_samples.then(Vec::new),
-        }
-    }
-
-    pub(crate) fn push_ns(&mut self, value: i128) {
-        self.running.push(value);
-        if let Some(samples) = self.samples.as_mut() {
-            samples.push(value);
-        }
-    }
-
-    pub(crate) fn stats(&self) -> TimeStats {
-        self.running
-            .stats(self.samples.as_ref().and_then(|samples| median_ns(samples)))
-    }
-}
-
-#[derive(Debug, Clone, PartialEq, Default)]
-struct RunningStats {
-    count: u64,
-    total_ns: i128,
-    min_ns: Option<i128>,
-    max_ns: Option<i128>,
-    mean_ns: f64,
-    m2_ns2: f64,
-}
-
-impl RunningStats {
-    fn push(&mut self, value: i128) {
-        self.count += 1;
-        self.total_ns = self.total_ns.saturating_add(value);
-        self.min_ns = Some(self.min_ns.map_or(value, |min| min.min(value)));
-        self.max_ns = Some(self.max_ns.map_or(value, |max| max.max(value)));
-        let x = value as f64;
-        let delta = x - self.mean_ns;
-        self.mean_ns += delta / self.count as f64;
-        let delta2 = x - self.mean_ns;
-        self.m2_ns2 += delta * delta2;
-    }
-
-    fn stats(&self, median_ns: Option<f64>) -> TimeStats {
-        TimeStats {
-            count: self.count,
-            total_ns: self.total_ns,
-            min_ns: self.min_ns,
-            max_ns: self.max_ns,
-            mean_ns: if self.count == 0 { 0.0 } else { self.mean_ns },
-            median_ns,
-            variance_ns2: sample_variance(self.count, self.m2_ns2),
-        }
-    }
-}
-
-fn sample_variance(count: u64, m2: f64) -> f64 {
-    if count < 2 {
-        0.0
-    } else {
-        m2 / (count - 1) as f64
-    }
-}
-
-fn median_ns(samples: &[i128]) -> Option<f64> {
-    if samples.is_empty() {
-        return None;
-    }
-    let mut sorted = samples.to_vec();
-    sorted.sort_unstable();
-    let mid = sorted.len() / 2;
-    Some(if sorted.len() % 2 == 1 {
-        sorted[mid] as f64
-    } else {
-        (sorted[mid - 1] as f64 + sorted[mid] as f64) / 2.0
-    })
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn running_duration_stats_use_sample_variance() {
-        let mut metric = TimeMetric::new(false);
-        metric.push_ns(1);
-        metric.push_ns(2);
-        metric.push_ns(3);
-        let stats = metric.stats();
-        assert_eq!(stats.count, 3);
-        assert_eq!(stats.total_ns, 6);
-        assert_eq!(stats.min_ns, Some(1));
-        assert_eq!(stats.max_ns, Some(3));
-        assert_eq!(stats.mean_ns, 2.0);
-        assert_eq!(stats.variance_ns2, 1.0);
-        assert_eq!(stats.stddev_ns(), 1.0);
-    }
-
-    #[test]
-    fn exact_median_handles_odd_and_even_samples() {
-        assert_eq!(median_ns(&[3, 1, 2]), Some(2.0));
-        assert_eq!(median_ns(&[4, 1, 2, 3]), Some(2.5));
-        assert_eq!(median_ns(&[-5, 1, 3]), Some(1.0));
-        assert_eq!(median_ns(&[-5, 1, 3, 7]), Some(2.0));
-    }
-
-    #[test]
-    fn single_sample_stddev_is_zero() {
-        let mut metric = TimeMetric::new(false);
-        metric.push_ns(42);
-        let stats = metric.stats();
-        assert_eq!(stats.variance_ns2, 0.0);
-        assert_eq!(stats.stddev_ns(), 0.0);
-    }
-}