Fix isolate ptr memory leak (denoland#872)

Author: littledivy

core/runtime/jsrealm.rs

@@ -67,7 +67,7 @@ pub struct ContextState {
   // We don't explicitly re-read this prop but need the slice to live alongside
   // the context
   pub(crate) op_ctxs: Box<[OpCtx]>,
-  pub(crate) isolate: Option<*mut v8::OwnedIsolate>,
+  pub(crate) isolate: Option<*mut v8::Isolate>,
   pub(crate) exception_state: Rc<ExceptionState>,
   pub(crate) has_next_tick_scheduled: Cell<bool>,
   pub(crate) get_error_class_fn: GetErrorClassFn,
@@ -77,7 +77,7 @@ pub struct ContextState {
 impl ContextState {
   pub(crate) fn new(
     op_driver: Rc<OpDriverImpl>,
-    isolate_ptr: *mut v8::OwnedIsolate,
+    isolate_ptr: *mut v8::Isolate,
     get_error_class_fn: GetErrorClassFn,
     op_ctxs: Box<[OpCtx]>,
     external_ops_tracker: ExternalOpsTracker,

core/runtime/jsruntime.rs

@@ -934,20 +934,12 @@ impl JsRuntime {
       );
     }
 
+    let isolate_ptr = isolate.as_mut() as *mut Isolate;
     // ...isolate is fully set up, we can forward its pointer to the ops to finish
     // their' setup...
     for op_ctx in op_ctxs.iter_mut() {
-      op_ctx.isolate = isolate.as_mut() as *mut Isolate;
+      op_ctx.isolate = isolate_ptr;
     }
-
-    // TODO(Bartlomieju): this can be simplified
-    let isolate_ptr = setup::create_isolate_ptr();
-    // SAFETY: this is first use of `isolate_ptr` so we are sure we're
-    // not overwriting an existing pointer.
-    isolate = unsafe {
-      isolate_ptr.write(isolate);
-      isolate_ptr.read()
-    };
     op_state.borrow_mut().put(isolate_ptr);
 
     let mut fast_fn_infos = Vec::with_capacity(op_ctxs.len());

core/runtime/setup.rs

@@ -118,20 +118,6 @@ fn create_cpp_heap() -> v8::UniqueRef<v8::cppgc::Heap> {
   )
 }
 
-pub fn create_isolate_ptr() -> *mut v8::OwnedIsolate {
-  let align = std::mem::align_of::<usize>();
-  let layout = std::alloc::Layout::from_size_align(
-    std::mem::size_of::<*mut v8::OwnedIsolate>(),
-    align,
-  )
-  .unwrap();
-  assert!(layout.size() > 0);
-  let isolate_ptr: *mut v8::OwnedIsolate =
-    // SAFETY: we just asserted that layout has non-0 size.
-    unsafe { std::alloc::alloc(layout) as *mut _ };
-  isolate_ptr
-}
-
 pub fn create_isolate(
   will_snapshot: bool,
   maybe_create_params: Option<v8::CreateParams>,