track-creation-site feature

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## [0.6.1] - 2025-11-02
+- add optional `track-creation-site` feature to store and print the location of `SendWrapper::new` during panics, to help debugging.
+
 ## [0.5.0] - 2020-10-14
 - add transparent wrapping of `Future` and `Stream` types via new cargo feature `futures`
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "send_wrapper"
-version = "0.6.0"
+version = "0.6.1"
 edition = "2018"
 authors = ["Thomas Keh"]
 license = "MIT/Apache-2.0"
@@ -17,6 +17,7 @@ categories = ["rust-patterns"]
 
 [features]
 futures = ["futures-core"]
+track-creation-site = []
 
 [dependencies]
 futures-core = { version = "0.3", optional = true }

src/lib.rs

@@ -46,9 +46,9 @@
 //!     // This would panic (because of dereferencing in wrong thread):
 //!     // let value = wrapped_value.deref();
 //!
-//! 	// Move SendWrapper back to main thread, so it can be dropped from there.
-//! 	// If you leave this out the thread will panic because of dropping from wrong thread.
-//! 	sender.send(wrapped_value).unwrap();
+//!     // Move SendWrapper back to main thread, so it can be dropped from there.
+//!     // If you leave this out the thread will panic because of dropping from wrong thread.
+//!     sender.send(wrapped_value).unwrap();
 //!
 //! });
 //!
@@ -99,22 +99,28 @@ mod futures;
 use std::fmt;
 use std::mem::{self, ManuallyDrop};
 use std::ops::{Deref, DerefMut, Drop};
+use std::panic::Location;
 use std::thread::{self, ThreadId};
 
 /// A wrapper which allows you to move around non-[`Send`]-types between threads, as long as you access the contained
 /// value only from within the original thread and make sure that it is dropped from within the original thread.
 pub struct SendWrapper<T> {
 	data: ManuallyDrop<T>,
 	thread_id: ThreadId,
+	#[cfg(feature = "track-creation-site")]
+	location: &'static Location<'static>,
 }
 
 impl<T> SendWrapper<T> {
 	/// Create a `SendWrapper<T>` wrapper around a value of type `T`.
 	/// The wrapper takes ownership of the value.
+	#[track_caller]
 	pub fn new(data: T) -> SendWrapper<T> {
 		SendWrapper {
 			data: ManuallyDrop::new(data),
 			thread_id: thread::current().id(),
+			#[cfg(feature = "track-creation-site")]
+			location: Location::caller(),
 		}
 	}
 
@@ -145,14 +151,24 @@ impl<T> SendWrapper<T> {
 	#[track_caller]
 	fn assert_valid_for_deref(&self) {
 		if !self.valid() {
-			invalid_deref()
+			invalid_deref(
+				#[cfg(feature = "track-creation-site")]
+				Some(self.location),
+				#[cfg(not(feature = "track-creation-site"))]
+				None,
+			)
 		}
 	}
 
 	#[track_caller]
 	fn assert_valid_for_poll(&self) {
 		if !self.valid() {
-			invalid_poll()
+			invalid_poll(
+				#[cfg(feature = "track-creation-site")]
+				Some(self.location),
+				#[cfg(not(feature = "track-creation-site"))]
+				None,
+			)
 		}
 	}
 }
@@ -176,7 +192,7 @@ impl<T> Deref for SendWrapper<T> {
 		// Access the value.
 		//
 		// Safety: We just checked that it is valid to access `T` on the current thread.
-		&*self.data
+		&self.data
 	}
 }
 
@@ -194,7 +210,7 @@ impl<T> DerefMut for SendWrapper<T> {
 		// Access the value.
 		//
 		// Safety: We just checked that it is valid to access `T` on the current thread.
-		&mut *self.data
+		&mut self.data
 	}
 }
 
@@ -227,7 +243,12 @@ impl<T> Drop for SendWrapper<T> {
 				ManuallyDrop::drop(&mut self.data);
 			}
 		} else {
-			invalid_drop()
+			invalid_drop(
+				#[cfg(feature = "track-creation-site")]
+				Some(self.location),
+				#[cfg(not(feature = "track-creation-site"))]
+				None,
+			);
 		}
 	}
 }
@@ -264,31 +285,52 @@ impl<T: Clone> Clone for SendWrapper<T> {
 #[cold]
 #[inline(never)]
 #[track_caller]
-fn invalid_deref() -> ! {
-	const DEREF_ERROR: &'static str = "Dereferenced SendWrapper<T> variable from a thread different to the one it has been created with.";
-
-	panic!("{}", DEREF_ERROR)
+fn invalid_deref(creation_site: Option<&Location<'static>>) -> ! {
+	const DEREF_ERROR: &str = "Dereferenced SendWrapper<T> variable from a thread different to the one it has been created with.";
+
+	panic!(
+		"{}{}",
+		DEREF_ERROR,
+		match creation_site {
+			Some(loc) => format!(" SendWrapper<T> created at {}", loc),
+			None => String::new(),
+		}
+	)
 }
 
 #[cold]
 #[inline(never)]
 #[track_caller]
-fn invalid_poll() -> ! {
-	const POLL_ERROR: &'static str = "Polling SendWrapper<T> variable from a thread different to the one it has been created with.";
-
-	panic!("{}", POLL_ERROR)
+fn invalid_poll(src: Option<&Location<'static>>) -> ! {
+	const POLL_ERROR: &str = "Polling SendWrapper<T> variable from a thread different to the one it has been created with.";
+
+	panic!(
+		"{}{}",
+		POLL_ERROR,
+		match src {
+			Some(loc) => format!(" SendWrapper<T> created at {}", loc),
+			None => String::new(),
+		}
+	)
 }
 
 #[cold]
 #[inline(never)]
 #[track_caller]
-fn invalid_drop() {
-	const DROP_ERROR: &'static str = "Dropped SendWrapper<T> variable from a thread different to the one it has been created with.";
+fn invalid_drop(creation_site: Option<&Location<'static>>) {
+	const DROP_ERROR: &str = "Dropped SendWrapper<T> variable from a thread different to the one it has been created with.";
 
 	if !std::thread::panicking() {
 		// panic because of dropping from wrong thread
 		// only do this while not unwinding (could be caused by deref from wrong thread)
-		panic!("{}", DROP_ERROR)
+		panic!(
+			"{}{}",
+			DROP_ERROR,
+			match creation_site {
+				Some(loc) => format!(" SendWrapper<T> created at {}", loc),
+				None => String::new(),
+			}
+		)
 	}
 }