Cache span field buffers

Signed-off-by: Alex Saveau <[email protected]>

tracing-tracy/src/lib.rs

@@ -49,7 +49,7 @@
 #![doc = include_str!("../FEATURES.mkd")]
 #![cfg_attr(tracing_tracy_docs, feature(doc_auto_cfg))]
 
-use std::{borrow::Cow, cell::UnsafeCell, collections::VecDeque, fmt::Write};
+use std::{borrow::Cow, cell::UnsafeCell, collections::VecDeque, fmt::Write, mem};
 use tracing_core::{
  field::{Field, Visit},
  span::{Attributes, Id, Record},
@@ -164,6 +164,10 @@ impl Default for TracyLayer {
  }
 }
 
+thread_local! {
+ static CACHE: VecCell<String> = const { VecCell::new() };
+}
+
 impl<S, F> Layer<S> for TracyLayer<F>
 where
  S: Subscriber + for<'a> registry::LookupSpan<'a>,
@@ -174,7 +178,8 @@ where
 
  let mut extensions = span.extensions_mut();
  if extensions.get_mut::<FormattedFields<F>>().is_none() {
- let mut fields = FormattedFields::<F>::new(String::with_capacity(64));
+ let mut fields =
+ FormattedFields::<F>::new(CACHE.with(|cache| cache.pop().unwrap_or_default()));
  if self.fmt.format_fields(fields.as_writer(), attrs).is_ok() {
  extensions.insert(fields);
  }
@@ -188,18 +193,15 @@ where
  if let Some(fields) = extensions.get_mut::<FormattedFields<F>>() {
  let _ = self.fmt.add_fields(fields, values);
  } else {
- let mut fields = FormattedFields::<F>::new(String::with_capacity(64));
+ let mut fields =
+ FormattedFields::<F>::new(CACHE.with(|cache| cache.pop().unwrap_or_default()));
  if self.fmt.format_fields(fields.as_writer(), values).is_ok() {
  extensions.insert(fields);
  }
  }
  }
 
  fn on_event(&self, event: &Event, _: Context<'_, S>) {
- thread_local! {
- static CACHE: VecCell<String> = const { VecCell::new() };
- }
-
  CACHE.with(|cache| {
  let mut buf = cache.pop().unwrap_or_default();
  let mut visitor = TracyEventFieldVisitor {
@@ -290,6 +292,18 @@ where
  );
  }
  }
+
+ fn on_close(&self, id: Id, ctx: Context<'_, S>) {
+ let Some(span_data) = ctx.span(&id) else {
+ return;
+ };
+
+ if let Some(fields) = span_data.extensions_mut().get_mut::<FormattedFields<F>>() {
+ let mut buf = mem::take(&mut fields.fields);
+ buf.clear();
+ CACHE.with(|cache| cache.push(buf));
+ };
+ }
 }
 
 struct TracyEventFieldVisitor<'a> {