fix: Optimize use of hash tables in platform adapters (#485)

Author: mwcampbell

Cargo.lock

@@ -17,7 +17,7 @@ default-target = "x86_64-apple-darwin"
 [dependencies]
 accesskit = { version = "0.17.0", path = "../../common" }
 accesskit_consumer = { version = "0.25.0", path = "../../consumer" }
-once_cell = "1.13.0"
+hashbrown = { version = "0.15", default-features = false, features = ["default-hasher"] }
 objc2 = "0.5.1"
 objc2-foundation = { version = "0.2.0", features = [
     "NSArray",

platforms/macos/Cargo.toml

@@ -5,10 +5,11 @@
 
 use accesskit::{ActionHandler, ActionRequest, NodeId};
 use accesskit_consumer::Tree;
+use hashbrown::HashMap;
 use objc2::rc::{Id, WeakId};
 use objc2_app_kit::*;
 use objc2_foundation::MainThreadMarker;
-use std::{cell::RefCell, collections::HashMap, rc::Rc};
+use std::{cell::RefCell, rc::Rc};
 
 use crate::node::PlatformNode;
 

platforms/macos/src/context.rs

@@ -5,10 +5,11 @@
 
 use accesskit::{Live, NodeId, Role};
 use accesskit_consumer::{FilterResult, Node, TreeChangeHandler};
+use hashbrown::HashSet;
 use objc2::runtime::{AnyObject, ProtocolObject};
 use objc2_app_kit::*;
 use objc2_foundation::{NSMutableDictionary, NSNumber, NSString};
-use std::{collections::HashSet, rc::Rc};
+use std::rc::Rc;
 
 use crate::{context::Context, filters::filter, node::NodeWrapper};
 

platforms/macos/src/event.rs

@@ -19,13 +19,11 @@ use objc2::{
 };
 use objc2_app_kit::{NSView, NSWindow};
 use objc2_foundation::{NSArray, NSObject, NSPoint};
-use once_cell::sync::Lazy;
-use std::{cell::RefCell, collections::HashMap, ffi::c_void, sync::Mutex};
+use std::{cell::RefCell, ffi::c_void, sync::Mutex};
 
 use crate::{event::QueuedEvents, Adapter};
 
-static SUBCLASSES: Lazy<Mutex<HashMap<&'static AnyClass, &'static AnyClass>>> =
-    Lazy::new(|| Mutex::new(HashMap::new()));
+static SUBCLASSES: Mutex<Vec<(&'static AnyClass, &'static AnyClass)>> = Mutex::new(Vec::new());
 
 static ASSOCIATED_OBJECT_KEY: u8 = 0;
 
@@ -163,34 +161,38 @@ impl SubclassingAdapter {
             )
         };
         let mut subclasses = SUBCLASSES.lock().unwrap();
-        let entry = subclasses.entry(prev_class);
-        let subclass = entry.or_insert_with(|| {
-            let name = format!("AccessKitSubclassOf{}", prev_class.name());
-            let mut builder = ClassBuilder::new(&name, prev_class).unwrap();
-            unsafe {
-                builder.add_method(
-                    sel!(superclass),
-                    superclass as unsafe extern "C" fn(_, _) -> _,
-                );
-                builder.add_method(
-                    sel!(accessibilityChildren),
-                    children as unsafe extern "C" fn(_, _) -> _,
-                );
-                builder.add_method(
-                    sel!(accessibilityFocusedUIElement),
-                    focus as unsafe extern "C" fn(_, _) -> _,
-                );
-                builder.add_method(
-                    sel!(accessibilityHitTest:),
-                    hit_test as unsafe extern "C" fn(_, _, _) -> _,
-                );
+        let subclass = match subclasses.iter().find(|entry| entry.0 == prev_class) {
+            Some(entry) => entry.1,
+            None => {
+                let name = format!("AccessKitSubclassOf{}", prev_class.name());
+                let mut builder = ClassBuilder::new(&name, prev_class).unwrap();
+                unsafe {
+                    builder.add_method(
+                        sel!(superclass),
+                        superclass as unsafe extern "C" fn(_, _) -> _,
+                    );
+                    builder.add_method(
+                        sel!(accessibilityChildren),
+                        children as unsafe extern "C" fn(_, _) -> _,
+                    );
+                    builder.add_method(
+                        sel!(accessibilityFocusedUIElement),
+                        focus as unsafe extern "C" fn(_, _) -> _,
+                    );
+                    builder.add_method(
+                        sel!(accessibilityHitTest:),
+                        hit_test as unsafe extern "C" fn(_, _, _) -> _,
+                    );
+                }
+                let class = builder.register();
+                subclasses.push((prev_class, class));
+                class
             }
-            builder.register()
-        });
+        };
         // SAFETY: Changing the view's class is only safe because
         // the subclass doesn't add any instance variables;
         // it uses an associated object instead.
-        unsafe { object_setClass(view as *mut _, (*subclass as *const AnyClass).cast()) };
+        unsafe { object_setClass(view as *mut _, (subclass as *const AnyClass).cast()) };
         Self {
             view: retained_view,
             associated,

platforms/macos/src/subclass.rs

@@ -18,6 +18,7 @@ targets = []
 [dependencies]
 accesskit = { version = "0.17.0", path = "../../common" }
 accesskit_consumer = { version = "0.25.0", path = "../../consumer" }
+hashbrown = { version = "0.15", default-features = false, features = ["default-hasher"] }
 paste = "1.0"
 static_assertions = "1.1.0"
 windows-core = "0.58.0"

platforms/windows/Cargo.toml

@@ -8,10 +8,8 @@ use accesskit::{
     TreeUpdate,
 };
 use accesskit_consumer::{FilterResult, Node, Tree, TreeChangeHandler};
-use std::{
-    collections::HashSet,
-    sync::{atomic::Ordering, Arc},
-};
+use hashbrown::HashSet;
+use std::sync::{atomic::Ordering, Arc};
 use windows::Win32::{
     Foundation::*,
     UI::{Accessibility::*, WindowsAndMessaging::*},