yield periodically in a tight and expensive loop

Summary:
## This stack

We noticed that the poll time is pretty high on some async methods, and that is affecting other calls as well. Let's try to optimize that.

## This diff

This ends up mattering a lot for some requests.

Reviewed By: singhsrb

Differential Revision: D67138693

fbshipit-source-id: f27e2a4fdf55d6f76a894362c8f94ac6c4f7cbd7

eden/mononoke/mononoke_api/src/sparse_profile.rs

@@ -21,6 +21,8 @@ use futures::try_join;
 use futures::FutureExt;
 use futures::StreamExt;
 use futures::TryStreamExt;
+use futures_ext::FbStreamExt;
+use futures_watchdog::WatchdogExt;
 use maplit::btreeset;
 use metaconfig_types::SparseProfilesConfig;
 use mononoke_types::fsnode::FsnodeEntry;
@@ -234,19 +236,24 @@ impl SparseProfileMonitoring {
 }
 
 pub(crate) async fn fetch<R: MononokeRepo>(
-    _ctx: &CoreContext,
+    ctx: &CoreContext,
     path: String,
     changeset: &ChangesetContext<R>,
 ) -> Result<Option<Vec<u8>>> {
     let path: &str = &path;
     let path = NonRootMPath::try_from(path)?;
-    let path_with_content = changeset.path_with_content(path.clone()).await?;
+    let path_with_content = changeset
+        .path_with_content(path.clone())
+        .watched(ctx.logger())
+        .await?;
     let file_ctx = path_with_content
         .file()
+        .watched(ctx.logger())
         .await?
         .ok_or_else(|| anyhow!("Sparse profile {} not found", path))?;
     file_ctx
         .content_concat()
+        .watched(ctx.logger())
         .await
         .with_context(|| format!("Couldn't fetch content of {path}"))
         .map(|b| Some(b.to_vec()))
@@ -258,13 +265,16 @@ async fn create_matchers<R: MononokeRepo>(
     paths: Vec<NonRootMPath>,
 ) -> Result<HashMap<String, Arc<dyn Matcher + Send + Sync>>> {
     stream::iter(paths)
+        .yield_periodically()
+        .with_logger(ctx.logger())
         .map(|path| async move {
             let content = format!("%include {path}");
             let dummy_source = "repo_root".to_string();
             let profile = sparse::Root::from_bytes(content.as_bytes(), dummy_source)
                 .with_context(|| format!("while constructing Profile for source {path}"))?;
             let matcher = profile
                 .matcher(|path| fetch(ctx, path, changeset))
+                .watched(ctx.logger())
                 .await
                 .with_context(|| format!("While constructing matcher for source {path}"))?;
             anyhow::Ok((
@@ -274,6 +284,7 @@ async fn create_matchers<R: MononokeRepo>(
         })
         .buffer_unordered(100)
         .try_collect()
+        .watched(ctx.logger())
         .await
 }
 
@@ -450,8 +461,12 @@ pub async fn get_profile_delta_size<R: MononokeRepo>(
     other: &ChangesetContext<R>,
     paths: Vec<NonRootMPath>,
 ) -> Result<HashMap<String, ProfileSizeChange>, MononokeError> {
-    let matchers = create_matchers(ctx, current, paths).await?;
-    calculate_delta_size(ctx, monitor, current, other, matchers).await
+    let matchers = create_matchers(ctx, current, paths)
+        .watched(ctx.logger())
+        .await?;
+    calculate_delta_size(ctx, monitor, current, other, matchers)
+        .watched(ctx.logger())
+        .await
 }
 
 pub async fn calculate_delta_size<'a, R: MononokeRepo>(