feat(linux): allow disabling WebViewUriLoader via feature

.changes/linux-request-queue-feature.md

@@ -0,0 +1,7 @@
+---
+wry: minor
+---
+
+Added `linux-request-queue` feature flag (enabled by default, which matches previous behavior).
+The queue prevents an unknown concurrency bug with loading multiple URIs at the same time on webkit2gtk.
+But it can introduce a deadlock situation under certain conditions (https://github.com/tauri-apps/tauri/issues/12589) and it prevents parallelization of request loading.

Cargo.toml

@@ -16,7 +16,7 @@ exclude = ["/.changes", "/.github", "/audits", "/wry-logo.svg"]
 
 [package.metadata.docs.rs]
 no-default-features = true
-features = ["drag-drop", "protocol", "os-webview"]
+features = ["drag-drop", "protocol", "os-webview", "linux-request-queue"]
 targets = [
   "x86_64-unknown-linux-gnu",
   "x86_64-pc-windows-msvc",
@@ -26,14 +26,15 @@ rustc-args = ["--cfg", "docsrs"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [features]
-default = ["drag-drop", "protocol", "os-webview", "x11"]
+default = ["drag-drop", "protocol", "os-webview", "x11", "linux-request-queue"]
 serde = ["dpi/serde"]
 drag-drop = []
 protocol = []
 devtools = []
 transparent = []
 fullscreen = []
 linux-body = ["webkit2gtk/v2_40", "os-webview"]
+linux-request-queue = []
 mac-proxy = []
 os-webview = [
   "javascriptcore-rs",

README.md

@@ -290,6 +290,10 @@ Wry uses a set of feature flags to toggle several advanced features.
   libraries and prevent from building documentation on doc.rs fails.
 - `linux-body`: Enables body support of custom protocol request on Linux. Requires
   webkit2gtk v2.40 or above.
+- `linux-request-queue` (default): Enables a request queue for webviews on Linux.
+  This Prevents an unknown concurrency bug with loading multiple URIs at the same time on webkit2gtk.
+  You might want to disable it because it can affect request performance, lead to a deadlock under certain conditions
+  and it might no longer be needed with newer WebKitGTK versions.
 - `tracing`: enables [`tracing`] for `evaluate_script`, `ipc_handler` and `custom_protocols.
 
 ### Partners

src/webkitgtk/mod.rs

@@ -362,8 +362,13 @@ impl InnerWebView {
 
     // Navigation
     if let Some(url) = attributes.url {
-      web_context.queue_load_uri(w.webview.clone(), url, attributes.headers);
-      web_context.flush_queue_loader();
+      #[cfg(feature = "linux-request-queue")]
+      {
+        web_context.queue_load_uri(w.webview.clone(), url, attributes.headers);
+        web_context.flush_queue_loader();
+      }
+      #[cfg(not(feature = "linux-request-queue"))]
+      web_context.load_uri(w.webview.clone(), url, attributes.headers);
     } else if let Some(html) = attributes.html {
       w.webview.load_html(&html, None);
     }

src/webkitgtk/web_context.rs

@@ -29,6 +29,7 @@ use webkit2gtk::{
 #[derive(Debug)]
 pub struct WebContextImpl {
   context: WebContext,
+  #[cfg(feature = "linux-request-queue")]
   webview_uri_loader: Rc<WebViewUriLoader>,
   automation: bool,
   app_info: Option<ApplicationInfo>,
@@ -83,6 +84,7 @@ impl WebContextImpl {
     Self {
       context,
       automation,
+      #[cfg(feature = "linux-request-queue")]
       webview_uri_loader: Rc::default(),
       app_info: Some(app_info),
     }
@@ -110,14 +112,20 @@ pub trait WebContextExt {
   where
     F: Fn(crate::WebViewId, Request<Vec<u8>>, RequestAsyncResponder) + 'static;
 
+  /// Directly loads a URI for a [`WebView`] bypassing the [`WebViewUriLoader`].
+  #[cfg(not(feature = "linux-request-queue"))]
+  fn load_uri(&self, webview: WebView, url: String, headers: Option<http::HeaderMap>);
+
   /// Add a [`WebView`] to the queue waiting to be opened.
   ///
   /// See the [`WebViewUriLoader`] for more information.
+  #[cfg(feature = "linux-request-queue")]
   fn queue_load_uri(&self, webview: WebView, url: String, headers: Option<http::HeaderMap>);
 
   /// Flush all queued [`WebView`]s waiting to load a uri.
   ///
   /// See the [`WebViewUriLoader`] for more information.
+  #[cfg(feature = "linux-request-queue")]
   fn flush_queue_loader(&self);
 
   /// If the context allows automation.
@@ -275,10 +283,32 @@ impl WebContextExt for super::WebContext {
     Ok(())
   }
 
+  #[cfg(not(feature = "linux-request-queue"))]
+  fn load_uri(&self, webview: WebView, uri: String, headers: Option<http::HeaderMap>) {
+    if let Some(headers) = headers {
+      let req = URIRequest::builder().uri(&uri).build();
+
+      if let Some(ref mut req_headers) = req.http_headers() {
+        for (header, value) in headers.iter() {
+          req_headers.append(
+            header.to_string().as_str(),
+            value.to_str().unwrap_or_default(),
+          );
+        }
+      }
+
+      webview.load_request(&req);
+    } else {
+      webview.load_uri(&uri);
+    }
+  }
+
+  #[cfg(feature = "linux-request-queue")]
   fn queue_load_uri(&self, webview: WebView, url: String, headers: Option<http::HeaderMap>) {
     self.os.webview_uri_loader.push(webview, url, headers)
   }
 
+  #[cfg(feature = "linux-request-queue")]
   fn flush_queue_loader(&self) {
     self.os.webview_uri_loader.clone().flush()
   }
@@ -409,12 +439,14 @@ struct WebviewUriRequest {
 /// FIXME: We think this may be an underlying concurrency bug in webkit2gtk as the usual ways of
 /// fixing threading issues are not working. Ideally, the locks are not needed if we can understand
 /// the true cause of the bug.
+#[cfg(feature = "linux-request-queue")]
 #[derive(Debug, Default)]
 struct WebViewUriLoader {
   lock: AtomicBool,
   queue: Mutex<VecDeque<WebviewUriRequest>>,
 }
 
+#[cfg(feature = "linux-request-queue")]
 impl WebViewUriLoader {
   /// Check if the lock is in use.
   fn is_locked(&self) -> bool {