Auto merge of #23139 - gterzian:bounded_profiler_with_buffer_feedback, r=jdm

Bound sampler buffer, add length feedback message, fix intermittence in test

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #23109 (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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2 files changed, 21 insertions, 8 deletions

diff --git a/components/background_hang_monitor/background_hang_monitor.rs b/components/background_hang_monitor/background_hang_monitor.rs
index 904e9a7ebd6..5791401fcd7 100644
--- a/components/background_hang_monitor/background_hang_monitor.rs
+++ b/components/background_hang_monitor/background_hang_monitor.rs
@@ -12,7 +12,7 @@ use msg::constellation_msg::{
 };
 use msg::constellation_msg::{HangAlert, HangAnnotation, HangMonitorAlert, SamplerControlMsg};
 use std::cell::Cell;
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::thread;
 use std::time::{Duration, Instant};
 
@@ -158,10 +158,11 @@ pub struct BackgroundHangMonitorWorker {
     port: Receiver<(MonitoredComponentId, MonitoredComponentMsg)>,
     control_port: Receiver<SamplerControlMsg>,
     sampling_duration: Option<Duration>,
+    sampling_max_duration: Option<Duration>,
     last_sample: Instant,
     creation: Instant,
     sampling_baseline: Instant,
-    samples: Vec<Sample>,
+    samples: VecDeque<Sample>,
 }
 
 impl BackgroundHangMonitorWorker {
@@ -178,10 +179,11 @@ impl BackgroundHangMonitorWorker {
             port,
             control_port,
             sampling_duration: None,
+            sampling_max_duration: None,
             last_sample: Instant::now(),
             sampling_baseline: Instant::now(),
             creation: Instant::now(),
-            samples: vec![],
+            samples: Default::default(),
         }
     }
 
@@ -244,9 +246,10 @@ impl BackgroundHangMonitorWorker {
             },
             recv(self.control_port) -> event => {
                 match event {
-                    Ok(SamplerControlMsg::Enable(rate)) => {
+                    Ok(SamplerControlMsg::Enable(rate, max_duration)) => {
                         println!("Enabling profiler.");
                         self.sampling_duration = Some(rate);
+                        self.sampling_max_duration = Some(max_duration);
                         self.sampling_baseline = Instant::now();
                         None
                     }
@@ -386,9 +389,15 @@ impl BackgroundHangMonitorWorker {
         for (component_id, monitored) in self.monitored_components.iter_mut() {
             let instant = Instant::now();
             if let Ok(stack) = monitored.sampler.suspend_and_sample_thread() {
-                // TODO: support a bounded buffer that discards older samples.
+                if self.sampling_baseline.elapsed() >
+                    self.sampling_max_duration
+                        .expect("Max duration has been set")
+                {
+                    // Buffer is full, start discarding older samples.
+                    self.samples.pop_front();
+                }
                 self.samples
-                    .push(Sample(component_id.clone(), instant, stack));
+                    .push_back(Sample(component_id.clone(), instant, stack));
             }
         }
     }
diff --git a/components/background_hang_monitor/tests/hang_monitor_tests.rs b/components/background_hang_monitor/tests/hang_monitor_tests.rs
index 8bc0700fa2e..bc783a49709 100644
--- a/components/background_hang_monitor/tests/hang_monitor_tests.rs
+++ b/components/background_hang_monitor/tests/hang_monitor_tests.rs
@@ -40,11 +40,15 @@ fn test_sampler() {
     );
 
     const RATE: u64 = 10;
+    const MAX_DURATION: u64 = 10;
     sampler_sender
-        .send(SamplerControlMsg::Enable(Duration::from_millis(RATE)))
+        .send(SamplerControlMsg::Enable(
+            Duration::from_millis(RATE),
+            Duration::from_secs(MAX_DURATION),
+        ))
         .unwrap();
 
-    thread::sleep(Duration::from_millis(30));
+    thread::sleep(Duration::from_millis(100));
 
     sampler_sender.send(SamplerControlMsg::Disable).unwrap();