Explicit panic instead of silent memory corruption (#1377)

Due to the automatic entry and exit behavior of Isolate upon creation and drop, it is crucial to ensure that v8::OwnedIsolate instances are dropped in the reverse order of their creation. Dropping them in the incorrect order can result in the corruption of the thread-local stack managed by v8, leading to memory corruption and potential segfaults. This introduces a check to verify the `this == Isolate::GetCurrent()` requirement before invoking the exit function. If the requirement is not met, a clean panic is triggered to provide explicit error handling instead of allowing silent memory corruption.

src/binding.cc

@@ -161,6 +161,8 @@ void v8__Isolate__Enter(v8::Isolate* isolate) { isolate->Enter(); }
 
 void v8__Isolate__Exit(v8::Isolate* isolate) { isolate->Exit(); }
 
+v8::Isolate* v8__Isolate__GetCurrent() { return v8::Isolate::GetCurrent(); }
+
 void v8__Isolate__MemoryPressureNotification(v8::Isolate* isolate,
                                              v8::MemoryPressureLevel level) {
   isolate->MemoryPressureNotification(level);

src/isolate.rs

@@ -379,6 +379,7 @@ extern "C" {
   fn v8__Isolate__GetNumberOfDataSlots(this: *const Isolate) -> u32;
   fn v8__Isolate__Enter(this: *mut Isolate);
   fn v8__Isolate__Exit(this: *mut Isolate);
+  fn v8__Isolate__GetCurrent() -> *mut Isolate;
   fn v8__Isolate__MemoryPressureNotification(this: *mut Isolate, level: u8);
   fn v8__Isolate__ClearKeptObjects(isolate: *mut Isolate);
   fn v8__Isolate__LowMemoryNotification(isolate: *mut Isolate);
@@ -534,7 +535,8 @@ extern "C" {
 /// synchronize.
 ///
 /// rusty_v8 note: Unlike in the C++ API, the Isolate is entered when it is
-/// constructed and exited when dropped.
+/// constructed and exited when dropped. Because of that v8::OwnedIsolate
+/// instances must be dropped in the reverse order of creation
 #[repr(C)]
 #[derive(Debug)]
 pub struct Isolate(Opaque);
@@ -1518,6 +1520,11 @@ impl Drop for OwnedIsolate {
         snapshot_creator.is_none(),
         "If isolate was created using v8::Isolate::snapshot_creator, you should use v8::OwnedIsolate::create_blob before dropping an isolate."
       );
+      // Safety: We need to check `this == Isolate::GetCurrent()` before calling exit()
+      assert!(
+        self.cxx_isolate.as_mut() as *mut Isolate == v8__Isolate__GetCurrent(),
+        "v8::OwnedIsolate instances must be dropped in the reverse order of creation. They are entered upon creation and exited upon being dropped."
+      );
       self.exit();
       self.cxx_isolate.as_mut().clear_scope_and_annex();
       self.cxx_isolate.as_mut().dispose();

tests/test_api.rs

@@ -636,6 +636,17 @@ fn microtasks() {
   }
 }
 
+#[test]
+#[should_panic(
+  expected = "v8::OwnedIsolate instances must be dropped in the reverse order of creation. They are entered upon creation and exited upon being dropped."
+)]
+fn isolate_drop_order() {
+  let isolate1 = v8::Isolate::new(Default::default());
+  let isolate2 = v8::Isolate::new(Default::default());
+  drop(isolate1);
+  drop(isolate2);
+}
+
 #[test]
 fn get_isolate_from_handle() {
   extern "C" {