fix(test): synchronize top-disk fixture writes with sampling (#8243)

rustfs/src/connect/diagnostics/top_disk.rs

@@ -22,6 +22,9 @@ use super::top_api::{MAX_SAFE_INTEGER, TopCaptureError, TopCaptureRequest, TopRe
 const TOOL_ID: &str = "top.disk";
 pub const TOP_DISK_CAPABILITY: &str = "top.disk@1";
 
+#[cfg(all(test, target_os = "linux"))]
+pub(super) static AFTER_INITIAL_DISK_SNAPSHOT: std::sync::OnceLock<fn()> = std::sync::OnceLock::new();
+
 /// Closed local-service request for supported top tools: no process selector, paths, or supplied provenance.
 #[derive(Clone, Debug, Deserialize, Serialize)]
 #[serde(deny_unknown_fields, rename_all = "camelCase")]
@@ -89,6 +92,10 @@ pub async fn capture_top_disk(
         }
         let mut sampler = rustfs_io_metrics::ProcessSampler::new();
         let before = process_snapshot(&mut sampler)?;
+        #[cfg(test)]
+        if let Some(write_fixture_data) = AFTER_INITIAL_DISK_SNAPSHOT.get() {
+            write_fixture_data();
+        }
         if !request.wait_window(TOOL_ID, cancel).await? {
             return request.cancelled(TOOL_ID);
         }

rustfs/src/connect/diagnostics/trace_runtime.rs

@@ -2706,6 +2706,16 @@ mod tests {
         let Some(state) = std::env::var_os("RUSTFS_TEST_TOP_DISK_STATE") else {
             return;
         };
+        super::super::top_disk::AFTER_INITIAL_DISK_SNAPSHOT
+            .set(|| {
+                // Keep real writes between the collector's snapshots in this dedicated child.
+                let mut file = tempfile::tempfile().expect("create top.disk fixture file");
+                for _ in 0..32 {
+                    file.write_all(&[1u8; 4096]).expect("write top.disk fixture data");
+                }
+                file.sync_all().expect("flush top.disk fixture data");
+            })
+            .expect("install top.disk fixture writer once");
         let state = std::path::PathBuf::from(state);
         let stop = CancellationToken::new();
         let input_stop = stop.clone();
@@ -2715,12 +2725,7 @@ mod tests {
         });
         tokio::runtime::Runtime::new().unwrap().block_on(async {
             let runtime = spawn_local_trace_capture_runtime(&state, &stop).unwrap();
-            let mut file = tempfile::tempfile().unwrap();
-            while !stop.is_cancelled() {
-                file.write_all(&[1u8; 4096]).unwrap();
-                file.sync_all().unwrap();
-                tokio::time::sleep(Duration::from_millis(5)).await;
-            }
+            stop.cancelled().await;
             runtime.shutdown().await;
         });
     }