From ab9f55ab0144462c1bc46a1fc49fe3b18f4d0fa7 Mon Sep 17 00:00:00 2001
From: Nicolas <bircni@icloud.com>
Date: Fri, 27 Jun 2025 11:27:03 +0200
Subject: [PATCH] Fix crash in `egui_extras::FileLoader` after `forget_image`
 (#6995)

This pull request modifies the `BytesLoader` implementation for
`FileLoader` in `crates/egui_extras/src/loaders/file_loader.rs` to
improve thread safety and handle unexpected states more gracefully.

### Changes to thread safety and state handling:
* Updated the cache logic to check if the `uri` exists in the cache
before inserting the result. If the `uri` is not found, a log message is
added to indicate the loading was canceled. This change prevents
overwriting cache entries unexpectedly.

* Closes <https://github.com/emilk/egui/issues/6755>
* [x] I have followed the instructions in the PR template
---
 crates/egui/src/context.rs                    |  1 +
 crates/egui_extras/src/loaders/file_loader.rs | 13 +++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/crates/egui/src/context.rs b/crates/egui/src/context.rs
index 27a3fcd9..fb83a837 100644
--- a/crates/egui/src/context.rs
+++ b/crates/egui/src/context.rs
@@ -3446,6 +3446,7 @@ impl Context {
     /// Release all memory and textures related to the given image URI.
     ///
     /// If you attempt to load the image again, it will be reloaded from scratch.
+    /// Also this cancels any ongoing loading of the image.
     pub fn forget_image(&self, uri: &str) {
         use load::BytesLoader as _;
 
diff --git a/crates/egui_extras/src/loaders/file_loader.rs b/crates/egui_extras/src/loaders/file_loader.rs
index 9feaebf5..d13134e2 100644
--- a/crates/egui_extras/src/loaders/file_loader.rs
+++ b/crates/egui_extras/src/loaders/file_loader.rs
@@ -95,10 +95,15 @@ impl BytesLoader for FileLoader {
                             }
                             Err(err) => Err(err.to_string()),
                         };
-                        let prev = cache.lock().insert(uri.clone(), Poll::Ready(result));
-                        assert!(matches!(prev, Some(Poll::Pending)), "unexpected state");
-                        ctx.request_repaint();
-                        log::trace!("finished loading {uri:?}");
+                        let mut cache = cache.lock();
+                        if let std::collections::hash_map::Entry::Occupied(mut entry) = cache.entry(uri.clone()) {
+                            let entry = entry.get_mut();
+                            *entry = Poll::Ready(result);
+                            ctx.request_repaint();
+                            log::trace!("finished loading {uri:?}");
+                        } else {
+                            log::trace!("cancelled loading {uri:?}\nNote: This can happen if `forget_image` is called while the image is still loading.");
+                        }
                     }
                 })
                 .expect("failed to spawn thread");