feat(core): Add read_scope for read-only scope access

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### New Features
+
+- Added `sentry::read_scope` and `Hub::read_scope`, read-only counterparts to [`configure_scope`](https://docs.rs/sentry-core/0.48.4/sentry_core/fn.configure_scope.html) that avoid cloning the scope and writing it back. The `sentry-tracing` integration now uses this to resolve the parent span when creating a new span.
+
 ## 0.48.4
 
 ### New Features

sentry-core/src/api.rs

@@ -157,6 +157,28 @@ where
     Hub::with_active(|hub| hub.configure_scope(f))
 }
 
+/// Invokes a function with read-only access to the current scope.
+///
+/// The function is passed a shared reference to the [`Scope`].  Because there
+/// might currently not be a scope or client active it's possible that the
+/// callback might not be called at all.  As a result of this the return value
+/// of this closure must have a default that is returned in such cases.
+///
+/// # Examples
+///
+/// ```
+/// # sentry::test::with_captured_events(|| {
+/// let span = sentry::read_scope(|scope| scope.get_span());
+/// # });
+/// ```
+pub fn read_scope<F, R>(f: F) -> R
+where
+    R: Default,
+    F: FnOnce(&Scope) -> R,
+{
+    Hub::with_active(|hub| hub.read_scope(f))
+}
+
 /// Temporarily pushes a scope for a single call optionally reconfiguring it.
 ///
 /// This function takes two arguments: the first is a callback that is passed

sentry-core/src/hub.rs

@@ -216,6 +216,24 @@ impl Hub {
         }
     }
 
+    /// Invokes a function with read-only access to the current scope.
+    ///
+    /// See the global [`read_scope`](crate::read_scope)
+    /// for more documentation.
+    pub fn read_scope<F, R>(&self, f: F) -> R
+    where
+        R: Default,
+        F: FnOnce(&Scope) -> R,
+    {
+        use_without_client!(f);
+        with_client_impl! {{
+            // Clone the `Arc<Scope>` out so the callback runs without
+            // holding the stack lock, keeping reentrant hub calls safe.
+            let scope = self.inner.with(|stack| stack.top().scope.clone());
+            f(&scope)
+        }}
+    }
+
     /// Invokes a function that can modify the current scope.
     ///
     /// See the global [`configure_scope`](fn.configure_scope.html)

sentry-tracing/src/layer/mod.rs

@@ -309,7 +309,7 @@ where
             sentry_op.unwrap_or_else(|| format!("{}::{}", span.metadata().target(), span.name()));
 
         let hub = sentry_core::Hub::current();
-        let parent_sentry_span = hub.configure_scope(|scope| scope.get_span());
+        let parent_sentry_span = hub.read_scope(|scope| scope.get_span());
 
         let mut sentry_span: sentry_core::TransactionOrSpan = match &parent_sentry_span {
             Some(parent) => parent.start_child(&sentry_op, sentry_name).into(),

sentry/examples/performance-demo.rs

@@ -37,7 +37,7 @@ fn main_span1() {
         let transaction_ctx = sentry::TransactionContext::continue_from_span(
             "background transaction",
             "root span",
-            sentry::configure_scope(|scope| scope.get_span()),
+            sentry::read_scope(|scope| scope.get_span()),
         );
         thread::spawn(move || {
             let transaction = sentry::start_transaction(transaction_ctx);
@@ -76,7 +76,7 @@ fn wrap_in_span<F, R>(op: &str, description: &str, f: F) -> R
 where
     F: FnOnce() -> R,
 {
-    let parent = sentry::configure_scope(|scope| scope.get_span());
+    let parent = sentry::read_scope(|scope| scope.get_span());
     let span1: sentry::TransactionOrSpan = match &parent {
         Some(parent) => parent.start_child(op, description).into(),
         None => {

sentry/tests/test_basic.rs

@@ -35,9 +35,7 @@ fn test_event_trace_context_from_propagation_context() {
     let mut last_event_id = None::<Uuid>;
     let mut span = None;
     let events = sentry::test::with_captured_events(|| {
-        sentry::configure_scope(|scope| {
-            span = scope.get_span();
-        });
+        span = sentry::read_scope(|scope| scope.get_span());
         sentry::capture_message("Hello World!", sentry::Level::Warning);
         last_event_id = sentry::last_event_id();
     });
@@ -160,6 +158,22 @@ fn test_reentrant_configure_scope() {
     assert_eq!(events[0].tags["which_scope"], "scope1");
 }
 
+#[test]
+fn test_reentrant_read_scope() {
+    let events = sentry::test::with_captured_events(|| {
+        sentry::read_scope(|_scope| {
+            sentry::configure_scope(|scope| {
+                scope.set_tag("which_scope", "reentrant");
+            });
+        });
+
+        sentry::capture_message("look ma, no deadlock!", sentry::Level::Info);
+    });
+
+    assert_eq!(events.len(), 1);
+    assert_eq!(events[0].tags["which_scope"], "reentrant");
+}
+
 #[test]
 fn test_attached_stacktrace() {
     let logger = sentry_log::SentryLogger::new();