feat: cppgc NameProvider (#1528)

build.rs

@@ -157,6 +157,7 @@ fn build_binding() {
     .rustified_enum(".*UseCounterFeature")
     .allowlist_item("v8__.*")
     .allowlist_item("cppgc__.*")
+    .allowlist_item("RustObj")
     .generate()
     .expect("Unable to generate bindings");
 

src/binding.cc

@@ -3856,24 +3856,19 @@ void v8__PropertyDescriptor__set_configurable(v8::PropertyDescriptor* self,
 
 extern "C" {
 
-class RustObj;
+void rusty_v8_RustObj_trace(const RustObj*, cppgc::Visitor*);
+const char* rusty_v8_RustObj_get_name(const RustObj*);
+void rusty_v8_RustObj_drop(RustObj*);
 
-using RustTraceFn = void (*)(const RustObj* obj, cppgc::Visitor*);
-using RustDestroyFn = void (*)(const RustObj* obj);
+RustObj::~RustObj() { rusty_v8_RustObj_drop(this); }
 
-class RustObj final : public cppgc::GarbageCollected<RustObj> {
- public:
-  explicit RustObj(RustTraceFn trace, RustDestroyFn destroy)
-      : trace_(trace), destroy_(destroy) {}
+void RustObj::Trace(cppgc::Visitor* visitor) const {
+  rusty_v8_RustObj_trace(this, visitor);
+}
 
-  ~RustObj() { destroy_(this); }
-
-  void Trace(cppgc::Visitor* visitor) const { trace_(this, visitor); }
-
- private:
-  RustTraceFn trace_;
-  RustDestroyFn destroy_;
-};
+const char* RustObj::GetHumanReadableName() const {
+  return rusty_v8_RustObj_get_name(this);
+}
 
 RustObj* v8__Object__Unwrap(v8::Isolate* isolate, const v8::Object& wrapper,
                             v8::CppHeapPointerTag tag) {
@@ -3930,12 +3925,9 @@ void cppgc__heap__collect_garbage_for_testing(
   heap->CollectGarbageForTesting(stack_state);
 }
 
-RustObj* cppgc__make_garbage_collectable(v8::CppHeap* heap, size_t size,
-                                         RustTraceFn trace,
-                                         RustDestroyFn destroy) {
+RustObj* cppgc__make_garbage_collectable(v8::CppHeap* heap, size_t size) {
   return cppgc::MakeGarbageCollected<RustObj>(heap->GetAllocationHandle(),
-                                              cppgc::AdditionalBytes(size),
-                                              trace, destroy);
+                                              cppgc::AdditionalBytes(size));
 }
 
 void cppgc__Visitor__Trace__Member(cppgc::Visitor* visitor,

src/binding.hpp

@@ -11,8 +11,6 @@
  * and made available in `crate::binding` in rust.
  */
 
-class RustObj;
-
 static size_t v8__ScriptOrigin_SIZE = sizeof(v8::ScriptOrigin);
 
 static size_t cppgc__Member_SIZE = sizeof(cppgc::Member<RustObj>);

src/cppgc.rs

@@ -1,5 +1,6 @@
 // Copyright 2019-2021 the Deno authors. All rights reserved. MIT license
 
+use crate::binding::RustObj;
 use crate::platform::Platform;
 use crate::support::int;
 use crate::support::Opaque;
@@ -7,6 +8,8 @@ use crate::support::SharedRef;
 use crate::support::UniqueRef;
 use crate::Data;
 use crate::TracedReference;
+use std::ffi::c_char;
+use std::ffi::CStr;
 use std::marker::PhantomData;
 use std::ptr::NonNull;
 
@@ -24,8 +27,6 @@ extern "C" {
   fn cppgc__make_garbage_collectable(
     heap: *mut Heap,
     size: usize,
-    trace: TraceFn,
-    destroy: DestroyFn,
   ) -> *mut RustObj;
 
   fn cppgc__heap__enable_detached_garbage_collections_for_testing(
@@ -83,14 +84,42 @@ extern "C" {
   ) -> *mut RustObj;
 }
 
-type TraceFn = unsafe extern "C" fn(*const RustObj, *mut Visitor);
-type DestroyFn = unsafe extern "C" fn(*const RustObj);
+unsafe fn get_rust_obj<'s>(obj: *const RustObj) -> &'s dyn GarbageCollected {
+  &*std::mem::transmute::<[usize; 2], *mut dyn GarbageCollected>((*obj).data)
+}
 
-#[doc(hidden)]
-#[repr(C)]
-pub struct RustObj {
-  trace: TraceFn,
-  destroy: DestroyFn,
+unsafe fn get_rust_obj_mut<'s>(
+  obj: *mut RustObj,
+) -> &'s mut dyn GarbageCollected {
+  &mut *std::mem::transmute::<[usize; 2], *mut dyn GarbageCollected>(
+    (*obj).data,
+  )
+}
+
+#[no_mangle]
+unsafe extern "C" fn rusty_v8_RustObj_trace(
+  obj: *const RustObj,
+  visitor: *mut Visitor,
+) {
+  let r = get_rust_obj(obj);
+  r.trace(&*visitor);
+}
+
+#[no_mangle]
+unsafe extern "C" fn rusty_v8_RustObj_get_name(
+  obj: *const RustObj,
+) -> *const c_char {
+  let r = get_rust_obj(obj);
+  match r.get_name() {
+    Some(s) => s.as_ptr(),
+    None => std::ptr::null(),
+  }
+}
+
+#[no_mangle]
+unsafe extern "C" fn rusty_v8_RustObj_drop(obj: *mut RustObj) {
+  let r = get_rust_obj_mut(obj);
+  std::ptr::drop_in_place(r);
 }
 
 fn object_offset_for_rust_obj<T: GarbageCollected>() -> usize {
@@ -103,7 +132,10 @@ fn object_offset_for_rust_obj<T: GarbageCollected>() -> usize {
   std::mem::offset_of!(Calc<T>, data)
 }
 
-fn get_object_from_rust_obj<T: GarbageCollected>(
+/// # Safety
+///
+/// T must be the correct type for this specific RustObj
+unsafe fn get_object_from_rust_obj<T: GarbageCollected>(
   rust_obj: *const RustObj,
 ) -> *mut T {
   unsafe { rust_obj.byte_add(object_offset_for_rust_obj::<T>()) as *mut T }
@@ -276,7 +308,23 @@ impl Heap {
 
 /// Base trait for managed objects.
 pub trait GarbageCollected {
+  /// `trace` should call `Visitor::visit` for each
+  /// `Member`, `WeakMember`, or `TracedReference` in
+  /// by the managed object.
   fn trace(&self, _visitor: &Visitor) {}
+
+  /// Specifies a name for the garbage-collected object. Such names will never
+  /// be hidden, as they are explicitly specified by the user of this API.
+  ///
+  /// V8 may call this function while generating a heap snapshot or at other
+  /// times. If V8 is currently generating a heap snapshot (according to
+  /// HeapProfiler::IsTakingSnapshot), then the returned string must stay alive
+  /// until the snapshot generation has completed. Otherwise, the returned string
+  /// must stay alive forever. If you need a place to store a temporary string
+  /// during snapshot generation, use HeapProfiler::CopyNameForHeapSnapshot.
+  fn get_name(&self) -> Option<&'static CStr> {
+    None
+  }
 }
 
 /// Constructs an instance of T, which is a garbage collected type.
@@ -291,23 +339,10 @@ pub trait GarbageCollected {
 ///
 /// The caller must ensure that the returned pointer is always stored on
 /// the stack, or is safely moved into one of the other cppgc pointer types.
-pub unsafe fn make_garbage_collected<T: GarbageCollected>(
+pub unsafe fn make_garbage_collected<T: GarbageCollected + 'static>(
   heap: &Heap,
   obj: T,
 ) -> Ptr<T> {
-  unsafe extern "C" fn trace<T: GarbageCollected>(
-    obj: *const RustObj,
-    visitor: *mut Visitor,
-  ) {
-    let obj = unsafe { &*get_object_from_rust_obj::<T>(obj) };
-    obj.trace(unsafe { &*visitor });
-  }
-
-  unsafe extern "C" fn destroy<T: GarbageCollected>(obj: *const RustObj) {
-    let obj = get_object_from_rust_obj::<T>(obj);
-    std::ptr::drop_in_place(obj);
-  }
-
   let additional_bytes = (object_offset_for_rust_obj::<T>()
     - std::mem::size_of::<RustObj>())
     + std::mem::size_of::<T>();
@@ -316,13 +351,17 @@ pub unsafe fn make_garbage_collected<T: GarbageCollected>(
     cppgc__make_garbage_collectable(
       heap as *const Heap as *mut _,
       additional_bytes,
-      trace::<T>,
-      destroy::<T>,
     )
   };
 
   unsafe {
-    get_object_from_rust_obj::<T>(pointer).write(obj);
+    let inner = get_object_from_rust_obj::<T>(pointer);
+    inner.write(obj);
+
+    let rust_obj = &mut *pointer;
+    rust_obj.data = std::mem::transmute::<*mut dyn GarbageCollected, [usize; 2]>(
+      &mut *inner as &mut dyn GarbageCollected as *mut dyn GarbageCollected,
+    );
   }
 
   Ptr {

src/object.rs

@@ -1,7 +1,7 @@
+use crate::binding::RustObj;
 use crate::cppgc::GarbageCollected;
 use crate::cppgc::GetRustObj;
 use crate::cppgc::Ptr;
-use crate::cppgc::RustObj;
 use crate::isolate::Isolate;
 use crate::support::int;
 use crate::support::MapFnTo;

src/support.h

@@ -9,6 +9,8 @@
 #include <type_traits>
 #include <utility>
 
+#include "v8/include/cppgc/name-provider.h"
+#include "v8/include/v8-cppgc.h"
 #include "v8/include/v8.h"
 
 // Work around a bug in the V8 headers.
@@ -190,3 +192,12 @@ struct three_pointers_t {
   V(BigInt64Array)
 
 #endif  // SUPPORT_H_
+
+class RustObj final : public cppgc::GarbageCollected<RustObj>,
+                      public cppgc::NameProvider {
+ public:
+  ~RustObj();
+  void Trace(cppgc::Visitor* visitor) const;
+  const char* GetHumanReadableName() const final;
+  uintptr_t data[2];
+};

tests/test_cppgc.rs

@@ -44,6 +44,10 @@ fn cppgc_object_wrap() {
       TRACE_COUNT.fetch_add(1, Ordering::SeqCst);
       visitor.trace(&self.value);
     }
+
+    fn get_name(&self) -> Option<&'static std::ffi::CStr> {
+      Some(c"Eyecatcher")
+    }
   }
 
   impl Drop for Wrap {
@@ -134,6 +138,16 @@ fn cppgc_object_wrap() {
 
       assert_eq!(DROP_COUNT.load(Ordering::SeqCst), 0);
 
+      {
+        let mut vec = Vec::<u8>::new();
+        scope.take_heap_snapshot(|chunk| {
+          vec.extend_from_slice(chunk);
+          true
+        });
+        let s = std::str::from_utf8(&vec).unwrap();
+        assert!(s.contains("Eyecatcher"));
+      }
+
       scope.request_garbage_collection_for_testing(
         v8::GarbageCollectionType::Full,
       );