Benchmark for #957

CHANGELOG.md

@@ -7,6 +7,11 @@
 - Added a `Envelope::into_items` method, which returns an iterator over owned [`EnvelopeItem`s](https://docs.rs/sentry/0.46.2/sentry/protocol/enum.EnvelopeItem.html) in the [`Envelope`](https://docs.rs/sentry/0.46.2/sentry/struct.Envelope.html) ([#983](https://github.com/getsentry/sentry-rust/pull/983)).
 - Expose transport utilities ([#949](https://github.com/getsentry/sentry-rust/pull/949))
 
+### Fixes
+
+- Fixed thread corruption bug where `HubSwitchGuard` could be dropped on wrong thread ([#957](https://github.com/getsentry/sentry-rust/pull/957))
+  - **Breaking change**: `sentry_core::HubSwitchGuard` is now `!Send`, preventing it from being moved across threads. Code that previously sent the guard to another thread will no longer compile.
+
 ## 0.46.2
 
 ### New Features

docs/2026-02-24-tracing-hub-forking-benchmark-setup.md

@@ -0,0 +1,53 @@
+# Tracing hub-forking benchmark setup
+
+## What was added
+
+- `sentry-tracing/Cargo.toml`
+  - Added dev dependency: `criterion = "0.8.2"`
+  - Added bench target:
+    - `[[bench]]`
+    - `name = "tracing_layer_perf"`
+    - `harness = false`
+
+- `sentry-tracing/benches/tracing_layer_perf.rs`
+  - Criterion benchmarks for:
+    - `enter_exit_existing_span`
+    - `create_enter_exit_close_span`
+    - `reenter_same_span_depth2`
+    - `cross_thread_shared_span`
+  - Each scenario runs in:
+    - `sentry_active`
+    - `tracing_only_control`
+
+- `scripts/bench/compare-tracing-perf-master-vs-head.sh`
+  - Automates `origin/master` vs current branch comparison
+  - Creates/reuses a master worktree at `target/bench-worktrees/tracing-perf-master`
+  - Reuses current checkout as head candidate
+  - Runs identical `cargo bench` commands on both
+  - Saves artifacts to `target/bench-compare/<timestamp>/`
+  - Produces:
+    - raw logs
+    - commands used
+    - summary markdown table with deltas
+
+## How to run
+
+Full profile (default):
+
+```bash
+scripts/bench/compare-tracing-perf-master-vs-head.sh
+```
+
+Reduced profile:
+
+```bash
+scripts/bench/compare-tracing-perf-master-vs-head.sh --reduced
+```
+
+## Output
+
+Artifacts are written to:
+
+- `target/bench-compare/<timestamp>/summary.md`
+- `target/bench-compare/<timestamp>/commands.txt`
+- `target/bench-compare/<timestamp>/raw/`

scripts/bench/compare-tracing-perf-master-vs-head.sh

@@ -0,0 +1,160 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+profile="full"
+if [[ "${1:-}" == "--reduced" ]]; then
+  profile="reduced"
+fi
+
+if [[ "$profile" == "full" ]]; then
+  sample_size=100
+  measurement_time=10
+  warm_up_time=3
+else
+  sample_size=20
+  measurement_time=2
+  warm_up_time=1
+fi
+
+repo_root="$(git rev-parse --show-toplevel)"
+current_branch="$(git rev-parse --abbrev-ref HEAD)"
+head_sha="$(git rev-parse HEAD)"
+timestamp="$(date -u +%Y%m%dT%H%M%SZ)"
+
+worktree_root="$repo_root/target/bench-worktrees"
+master_worktree="$worktree_root/tracing-perf-master"
+head_worktree="$repo_root"
+
+artifact_dir="$repo_root/target/bench-compare/$timestamp"
+raw_dir="$artifact_dir/raw"
+mkdir -p "$raw_dir/master" "$raw_dir/head"
+
+mkdir -p "$worktree_root"
+
+git config --global --add safe.directory "$repo_root" >/dev/null 2>&1 || true
+git config --global --add safe.directory "$master_worktree" >/dev/null 2>&1 || true
+
+git fetch origin master >/dev/null
+
+if [[ ! -e "$master_worktree/.git" ]]; then
+  git worktree add --detach "$master_worktree" origin/master >/dev/null
+else
+  git -C "$master_worktree" fetch origin master >/dev/null
+  git -C "$master_worktree" checkout --detach -f origin/master >/dev/null
+fi
+
+# Keep benchmark harness identical between baseline and candidate.
+mkdir -p "$master_worktree/sentry-tracing/benches"
+cp "$repo_root/sentry-tracing/Cargo.toml" "$master_worktree/sentry-tracing/Cargo.toml"
+cp "$repo_root/sentry-tracing/benches/tracing_layer_perf.rs" "$master_worktree/sentry-tracing/benches/tracing_layer_perf.rs"
+cp "$repo_root/Cargo.lock" "$master_worktree/Cargo.lock"
+
+scenarios=(
+  enter_exit_existing_span
+  create_enter_exit_close_span
+  reenter_same_span_depth2
+  cross_thread_shared_span
+)
+
+modes=(
+  sentry_active
+  tracing_only_control
+)
+
+commands_file="$artifact_dir/commands.txt"
+{
+  echo "# profile=$profile"
+  echo "# branch=$current_branch"
+  echo "# head_sha=$head_sha"
+  echo "cargo bench -p sentry-tracing --bench tracing_layer_perf --no-run"
+  for scenario in "${scenarios[@]}"; do
+    echo "cargo bench -p sentry-tracing --bench tracing_layer_perf $scenario -- --sample-size $sample_size --measurement-time $measurement_time --warm-up-time $warm_up_time --noplot"
+  done
+} >"$commands_file"
+
+run_suite() {
+  local label="$1"
+  local worktree="$2"
+
+  (
+    cd "$worktree"
+    cargo bench -p sentry-tracing --bench tracing_layer_perf --no-run
+  ) >"$raw_dir/$label/build.log" 2>&1
+
+  for scenario in "${scenarios[@]}"; do
+    local log_file="$raw_dir/$label/$scenario.log"
+    (
+      cd "$worktree"
+      cargo bench -p sentry-tracing --bench tracing_layer_perf "$scenario" -- \
+        --sample-size "$sample_size" \
+        --measurement-time "$measurement_time" \
+        --warm-up-time "$warm_up_time" \
+        --noplot
+    ) 2>&1 | tee "$log_file"
+  done
+}
+
+parse_mean_ns() {
+  local log_file="$1"
+  local bench_name="$2"
+
+  awk -v bench="$bench_name" '
+    function to_ns(v, u) {
+      if (u == "ns") return v
+      if (u == "us" || u == "µs" || u == "μs") return v * 1000
+      if (u == "ms") return v * 1000000
+      if (u == "s") return v * 1000000000
+      return -1
+    }
+    /^Benchmarking / {
+      current = $0
+      sub(/^Benchmarking /, "", current)
+      sub(/:.*/, "", current)
+    }
+    $1 == "time:" && current == bench {
+      gsub("\\[", "", $2)
+      middle_value = $4
+      middle_unit = $5
+      print to_ns(middle_value + 0, middle_unit)
+      exit
+    }
+  ' "$log_file"
+}
+
+run_suite master "$master_worktree"
+run_suite head "$head_worktree"
+
+summary_file="$artifact_dir/summary.md"
+{
+  echo "# tracing_layer_perf: origin/master vs $current_branch"
+  echo
+  printf -- "- profile: \`%s\`\n" "$profile"
+  printf -- "- baseline: \`%s\`\n" "origin/master"
+  printf -- "- candidate: \`%s (%s)\`\n" "$current_branch" "$head_sha"
+  echo
+  echo "| scenario | mode | master mean (ns) | head mean (ns) | delta |"
+  echo "|---|---|---:|---:|---:|"
+
+  for scenario in "${scenarios[@]}"; do
+    for mode in "${modes[@]}"; do
+      bench_name="$scenario/$mode"
+      master_ns="$(parse_mean_ns "$raw_dir/master/$scenario.log" "$bench_name")"
+      head_ns="$(parse_mean_ns "$raw_dir/head/$scenario.log" "$bench_name")"
+
+      if [[ -z "$master_ns" || -z "$head_ns" ]]; then
+        delta="n/a"
+      else
+        delta="$(awk -v a="$master_ns" -v b="$head_ns" 'BEGIN { printf "%.2f%%", ((b - a) / a) * 100 }')"
+      fi
+
+      echo "| $scenario | $mode | $master_ns | $head_ns | $delta |"
+    done
+  done
+  echo
+  printf -- "Commands: \`%s\`\n" "$commands_file"
+  printf -- "Raw logs: \`%s\`\n" "$raw_dir"
+} >"$summary_file"
+
+echo "Benchmark comparison complete."
+echo "Artifacts: $artifact_dir"
+echo "Summary: $summary_file"

sentry-core/src/hub_impl.rs

@@ -1,5 +1,6 @@
 use std::cell::{Cell, UnsafeCell};
-use std::sync::{Arc, LazyLock, PoisonError, RwLock};
+use std::marker::PhantomData;
+use std::sync::{Arc, LazyLock, MutexGuard, PoisonError, RwLock};
 use std::thread;
 
 use crate::Scope;
@@ -19,10 +20,14 @@ thread_local! {
     );
 }
 
-/// A Hub switch guard used to temporarily swap
-/// active hub in thread local storage.
+/// A guard that temporarily swaps the active hub in thread-local storage.
+///
+/// This type is `!Send` because it manages thread-local state and must be
+/// dropped on the same thread where it was created.
 pub struct SwitchGuard {
     inner: Option<(Arc<Hub>, bool)>,
+    /// Makes this type `!Send` while keeping it `Sync`.
+    _not_send: PhantomData<MutexGuard<'static, ()>>,
 }
 
 impl SwitchGuard {
@@ -41,7 +46,10 @@ impl SwitchGuard {
             let was_process_hub = is_process_hub.replace(false);
             Some((hub, was_process_hub))
         });
-        SwitchGuard { inner }
+        SwitchGuard {
+            inner,
+            _not_send: PhantomData,
+        }
     }
 
     fn swap(&mut self) -> Option<Arc<Hub>> {

sentry-tracing/Cargo.toml

@@ -38,3 +38,8 @@ serde_json = "1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3.20", features = ["fmt", "registry"] }
 tokio = { version = "1.44", features = ["rt-multi-thread", "macros", "time"] }
+criterion = "0.8.2"
+
+[[bench]]
+name = "tracing_layer_perf"
+harness = false