fix(android): BorrowError crash when loading assets on Android

.changes/fix-android-race-condition.md

@@ -0,0 +1,5 @@
+---
+"wry": patch
+---
+
+Fix `already mutably borrowed: BorrowError` panic on webview initialization on Android.

src/android/binding.rs

@@ -106,7 +106,7 @@ fn handle_request(
   request: JObject,
   is_document_start_script_enabled: jboolean,
 ) -> JniResult<jobject> {
-  if let Some(handler) = REQUEST_HANDLER.borrow().as_ref() {
+  if let Some(handler) = REQUEST_HANDLER.lock().unwrap().as_ref() {
     #[cfg(feature = "tracing")]
     let span =
       tracing::info_span!(parent: None, "wry::custom_protocol::handle", uri = tracing::field::Empty).entered();
@@ -294,7 +294,8 @@ pub unsafe fn shouldOverride(mut env: JNIEnv, _: JClass, url: JString) -> jboole
     Ok(url) => {
       let url = url.to_string_lossy().to_string();
       URL_LOADING_OVERRIDE
-        .borrow()
+        .lock()
+        .unwrap()
         .as_ref()
         // We negate the result of the function because the logic for the android
         // client is different from how the navigation_handler is defined.
@@ -340,7 +341,7 @@ pub unsafe fn ipc(mut env: JNIEnv, _: JClass, url: JString, body: JString) {
 
       let url = url.to_string_lossy().to_string();
       let body = body.to_string_lossy().to_string();
-      if let Some(ipc) = IPC.borrow().as_ref() {
+      if let Some(ipc) = IPC.lock().unwrap().as_ref() {
         (ipc.handler)(Request::builder().uri(url).body(body).unwrap())
       }
     }
@@ -356,7 +357,7 @@ pub unsafe fn handleReceivedTitle(mut env: JNIEnv, _: JClass, _webview: JObject,
   match env.get_string(&title) {
     Ok(title) => {
       let title = title.to_string_lossy().to_string();
-      if let Some(title_handler) = TITLE_CHANGE_HANDLER.borrow().as_ref() {
+      if let Some(title_handler) = TITLE_CHANGE_HANDLER.lock().unwrap().as_ref() {
         (title_handler.handler)(title)
       }
     }
@@ -369,12 +370,12 @@ pub unsafe fn handleReceivedTitle(mut env: JNIEnv, _: JClass, _webview: JObject,
 
 #[allow(non_snake_case)]
 pub unsafe fn withAssetLoader(_: JNIEnv, _: JClass) -> jboolean {
-  (*WITH_ASSET_LOADER.borrow().as_ref().unwrap_or(&false)).into()
+  (*WITH_ASSET_LOADER.lock().unwrap().as_ref().unwrap_or(&false)).into()
 }
 
 #[allow(non_snake_case)]
 pub unsafe fn assetLoaderDomain(env: JNIEnv, _: JClass) -> jstring {
-  if let Some(domain) = ASSET_LOADER_DOMAIN.borrow().as_ref() {
+  if let Some(domain) = ASSET_LOADER_DOMAIN.lock().unwrap().as_ref() {
     env.new_string(domain).unwrap().as_raw()
   } else {
     env.new_string("wry.assets").unwrap().as_raw()
@@ -386,7 +387,7 @@ pub unsafe fn onPageLoading(mut env: JNIEnv, _: JClass, url: JString) {
   match env.get_string(&url) {
     Ok(url) => {
       let url = url.to_string_lossy().to_string();
-      if let Some(on_load) = ON_LOAD_HANDLER.borrow().as_ref() {
+      if let Some(on_load) = ON_LOAD_HANDLER.lock().unwrap().as_ref() {
         (on_load.handler)(PageLoadEvent::Started, url)
       }
     }
@@ -402,7 +403,7 @@ pub unsafe fn onPageLoaded(mut env: JNIEnv, _: JClass, url: JString) {
   match env.get_string(&url) {
     Ok(url) => {
       let url = url.to_string_lossy().to_string();
-      if let Some(on_load) = ON_LOAD_HANDLER.borrow().as_ref() {
+      if let Some(on_load) = ON_LOAD_HANDLER.lock().unwrap().as_ref() {
         (on_load.handler)(PageLoadEvent::Finished, url)
       }
     }

src/android/mod.rs

@@ -23,7 +23,6 @@ use raw_window_handle::HasWindowHandle;
 use sha2::{Digest, Sha256};
 use std::{
   borrow::Cow,
-  cell::RefCell,
   collections::HashMap,
   os::fd::{AsFd as _, AsRawFd as _},
   sync::{mpsc::channel, Mutex},
@@ -45,13 +44,13 @@ pub struct Context<'a, 'b> {
   pub webview: &'a JObject<'b>,
 }
 
-pub(crate) struct StaticCell<T>(RefCell<T>);
+pub(crate) struct StaticValue<T>(Mutex<T>);
 
-unsafe impl<T> Send for StaticCell<T> {}
-unsafe impl<T> Sync for StaticCell<T> {}
+unsafe impl<T> Send for StaticValue<T> {}
+unsafe impl<T> Sync for StaticValue<T> {}
 
-impl<T> std::ops::Deref for StaticCell<T> {
-  type Target = RefCell<T>;
+impl<T> std::ops::Deref for StaticValue<T> {
+  type Target = Mutex<T>;
 
   fn deref(&self) -> &Self::Target {
     &self.0
@@ -60,7 +59,7 @@ impl<T> std::ops::Deref for StaticCell<T> {
 
 macro_rules! define_static_handlers {
   ($($var:ident = $type_name:ident { $($fields:ident:$types:ty),+ $(,)? });+ $(;)?) => {
-    $(pub static $var: StaticCell<Option<$type_name>> = StaticCell(RefCell::new(None));
+    $(pub static $var: StaticValue<Option<$type_name>> = StaticValue(Mutex::new(None));
     pub struct $type_name {
       $($fields: $types,)*
     }
@@ -84,8 +83,8 @@ define_static_handlers! {
   ON_LOAD_HANDLER = UnsafeOnPageLoadHandler { handler: Box<dyn Fn(PageLoadEvent, String)> };
 }
 
-pub static WITH_ASSET_LOADER: StaticCell<Option<bool>> = StaticCell(RefCell::new(None));
-pub static ASSET_LOADER_DOMAIN: StaticCell<Option<String>> = StaticCell(RefCell::new(None));
+pub static WITH_ASSET_LOADER: StaticValue<Option<bool>> = StaticValue(Mutex::new(None));
+pub static ASSET_LOADER_DOMAIN: StaticValue<Option<String>> = StaticValue(Mutex::new(None));
 
 pub(crate) static PACKAGE: OnceCell<String> = OnceCell::new();
 
@@ -208,27 +207,14 @@ impl InnerWebView {
       .map(|id| id.to_string())
       .unwrap_or_else(|| COUNTER.next().to_string());
 
-    MainPipe::send(WebViewMessage::CreateWebView(CreateWebViewAttributes {
-      id: id.clone(),
-      url,
-      html,
-      #[cfg(any(debug_assertions, feature = "devtools"))]
-      devtools,
-      background_color,
-      transparent,
-      headers,
-      on_webview_created,
-      autoplay,
-      user_agent,
-      initialization_scripts: initialization_scripts.clone(),
-    }));
-
-    WITH_ASSET_LOADER.replace(Some(with_asset_loader));
+    WITH_ASSET_LOADER.lock().unwrap().replace(with_asset_loader);
     if let Some(domain) = asset_loader_domain {
-      ASSET_LOADER_DOMAIN.replace(Some(domain));
+      ASSET_LOADER_DOMAIN.lock().unwrap().replace(domain);
     }
 
-    REQUEST_HANDLER.replace(Some(
+    let initialization_scripts_ = initialization_scripts.clone();
+    REQUEST_HANDLER.lock()
+        .unwrap().replace(
       UnsafeRequestHandler::new(Box::new(
         move |webview_id: &str, mut request, is_document_start_script_enabled| {
           let uri = request.uri().to_string();
@@ -247,7 +233,7 @@ impl InnerWebView {
             }
 
             let (tx, rx) = channel();
-            let initialization_scripts = initialization_scripts.clone();
+            let initialization_scripts = initialization_scripts_.clone();
             let responder: Box<dyn FnOnce(HttpResponse<Cow<'static, [u8]>>)> =
               Box::new(move |mut response| {
                 if !is_document_start_script_enabled {
@@ -309,25 +295,49 @@ impl InnerWebView {
           }
           None
         },
-      ))
+      )
     ));
 
     if let Some(i) = ipc_handler {
-      IPC.replace(Some(UnsafeIpc::new(Box::new(i))));
+      IPC.lock().unwrap().replace(UnsafeIpc::new(Box::new(i)));
     }
 
     if let Some(i) = attributes.document_title_changed_handler {
-      TITLE_CHANGE_HANDLER.replace(Some(UnsafeTitleHandler::new(i)));
+      TITLE_CHANGE_HANDLER
+        .lock()
+        .unwrap()
+        .replace(UnsafeTitleHandler::new(i));
     }
 
     if let Some(i) = attributes.navigation_handler {
-      URL_LOADING_OVERRIDE.replace(Some(UnsafeUrlLoadingOverride::new(i)));
+      URL_LOADING_OVERRIDE
+        .lock()
+        .unwrap()
+        .replace(UnsafeUrlLoadingOverride::new(i));
     }
 
     if let Some(h) = attributes.on_page_load_handler {
-      ON_LOAD_HANDLER.replace(Some(UnsafeOnPageLoadHandler::new(h)));
+      ON_LOAD_HANDLER
+        .lock()
+        .unwrap()
+        .replace(UnsafeOnPageLoadHandler::new(h));
     }
 
+    MainPipe::send(WebViewMessage::CreateWebView(CreateWebViewAttributes {
+      id: id.clone(),
+      url,
+      html,
+      #[cfg(any(debug_assertions, feature = "devtools"))]
+      devtools,
+      background_color,
+      transparent,
+      headers,
+      on_webview_created,
+      autoplay,
+      user_agent,
+      initialization_scripts,
+    }));
+
     Ok(Self { id })
   }