Add IsolateHandle (#274)

Co-authored-by: Bert Belder <bertbelder@gmail.com>

src/global.rs

@@ -3,6 +3,7 @@ use std::ptr::NonNull;
 
 use crate::InIsolate;
 use crate::Isolate;
+use crate::IsolateHandle;
 use crate::Local;
 use crate::ToLocal;
 use crate::Value;
@@ -34,17 +35,15 @@ extern "C" {
 #[repr(C)]
 pub struct Global<T> {
   value: Option<NonNull<T>>,
-  isolate: Option<NonNull<Isolate>>,
+  isolate_handle: Option<IsolateHandle>,
 }
 
-unsafe impl<T> Send for Global<T> {}
-
 impl<T> Global<T> {
   /// Construct a Global with no storage cell.
   pub fn new() -> Self {
     Self {
       value: None,
-      isolate: None,
+      isolate_handle: None,
     }
   }
 
@@ -60,7 +59,7 @@ impl<T> Global<T> {
     Self {
       value: other_value
         .map(|v| unsafe { transmute(v8__Global__New(isolate, transmute(v))) }),
-      isolate: other_value.map(|_| isolate.into()),
+      isolate_handle: other_value.map(|_| IsolateHandle::new(isolate)),
     }
   }
 
@@ -105,7 +104,7 @@ impl<T> Global<T> {
         )
       },
     }
-    self.isolate = other_value.map(|_| isolate.into());
+    self.isolate_handle = other_value.map(|_| IsolateHandle::new(isolate));
   }
 
   /// If non-empty, destroy the underlying storage cell
@@ -114,10 +113,13 @@ impl<T> Global<T> {
     self.set(scope, None);
   }
 
-  fn check_isolate(&self, other: &Isolate) {
+  fn check_isolate(&self, isolate: &mut Isolate) {
     match self.value {
-      None => assert_eq!(self.isolate, None),
-      Some(_) => assert_eq!(self.isolate.unwrap(), other.into()),
+      None => assert!(self.isolate_handle.is_none()),
+      Some(_) => assert_eq!(
+        unsafe { self.isolate_handle.as_ref().unwrap().get_isolate_ptr() },
+        isolate as *mut _
+      ),
     }
   }
 }
@@ -130,30 +132,52 @@ impl<T> Default for Global<T> {
 
 impl<T> Drop for Global<T> {
   fn drop(&mut self) {
-    if !self.is_empty() {
-      panic!("Global handle dropped while holding a value");
+    match &mut self.value {
+      None => {
+        // This global handle is empty.
+        assert!(self.isolate_handle.is_none())
+      }
+      Some(_)
+        if unsafe {
+          self
+            .isolate_handle
+            .as_ref()
+            .unwrap()
+            .get_isolate_ptr()
+            .is_null()
+        } =>
+      {
+        // This global handle is associated with an Isolate that has already
+        // been disposed.
+      }
+      addr @ Some(_) => unsafe {
+        // Destroy the storage cell that contains the contents of this Global.
+        v8__Global__Reset__0(
+          &mut *(addr as *mut Option<NonNull<T>> as *mut *mut Value),
+        )
+      },
     }
   }
 }
 
 pub trait AnyHandle<T> {
-  fn read(self, isolate: &Isolate) -> Option<NonNull<T>>;
+  fn read(self, isolate: &mut Isolate) -> Option<NonNull<T>>;
 }
 
 impl<'sc, T> AnyHandle<T> for Local<'sc, T> {
-  fn read(self, _isolate: &Isolate) -> Option<NonNull<T>> {
+  fn read(self, _isolate: &mut Isolate) -> Option<NonNull<T>> {
     Some(self.as_non_null())
   }
 }
 
 impl<'sc, T> AnyHandle<T> for Option<Local<'sc, T>> {
-  fn read(self, _isolate: &Isolate) -> Option<NonNull<T>> {
+  fn read(self, _isolate: &mut Isolate) -> Option<NonNull<T>> {
     self.map(|local| local.as_non_null())
   }
 }
 
 impl<'sc, T> AnyHandle<T> for &Global<T> {
-  fn read(self, isolate: &Isolate) -> Option<NonNull<T>> {
+  fn read(self, isolate: &mut Isolate) -> Option<NonNull<T>> {
     self.check_isolate(isolate);
     self.value
   }

src/isolate.rs

@@ -18,10 +18,15 @@ use crate::ScriptOrModule;
 use crate::StartupData;
 use crate::String;
 use crate::Value;
+
 use std::ffi::c_void;
+use std::mem::replace;
 use std::ops::Deref;
 use std::ops::DerefMut;
+use std::ptr::null_mut;
 use std::ptr::NonNull;
+use std::sync::Arc;
+use std::sync::Mutex;
 
 pub type MessageCallback = extern "C" fn(Local<Message>, Local<Value>);
 
@@ -161,22 +166,26 @@ impl Isolate {
     CreateParams::new()
   }
 
+  pub fn thread_safe_handle(&mut self) -> IsolateHandle {
+    IsolateHandle::new(self)
+  }
+
   /// Associate embedder-specific data with the isolate. |slot| has to be
   /// between 0 and GetNumberOfDataSlots() - 1.
   pub unsafe fn set_data(&mut self, slot: u32, ptr: *mut c_void) {
-    v8__Isolate__SetData(self, slot, ptr)
+    v8__Isolate__SetData(self, slot + 1, ptr)
   }
 
   /// Retrieve embedder-specific data from the isolate.
   /// Returns NULL if SetData has never been called for the given |slot|.
   pub fn get_data(&self, slot: u32) -> *mut c_void {
-    unsafe { v8__Isolate__GetData(self, slot) }
+    unsafe { v8__Isolate__GetData(self, slot + 1) }
   }
 
   /// Returns the maximum number of available embedder data slots. Valid slots
   /// are in the range of 0 - GetNumberOfDataSlots() - 1.
   pub fn get_number_of_data_slots(&self) -> u32 {
-    unsafe { v8__Isolate__GetNumberOfDataSlots(self) }
+    unsafe { v8__Isolate__GetNumberOfDataSlots(self) - 1 }
   }
 
   /// Sets this isolate as the entered one for the current thread.
@@ -283,23 +292,97 @@ impl Isolate {
     }
   }
 
+  /// Runs the default MicrotaskQueue until it gets empty.
+  /// Any exceptions thrown by microtask callbacks are swallowed.
+  pub fn run_microtasks(&mut self) {
+    unsafe { v8__Isolate__RunMicrotasks(self) }
+  }
+
+  /// Enqueues the callback to the default MicrotaskQueue
+  pub fn enqueue_microtask(&mut self, microtask: Local<Function>) {
+    unsafe { v8__Isolate__EnqueueMicrotask(self, microtask) }
+  }
+
+  /// Disposes the isolate.  The isolate must not be entered by any
+  /// thread to be disposable.
+  unsafe fn dispose(&mut self) {
+    IsolateHandle::dispose(self);
+    v8__Isolate__Dispose(self)
+  }
+}
+
+pub(crate) struct IsolateAnnex {
+  isolate: *mut Isolate,
+  mutex: Mutex<()>,
+}
+
+impl IsolateAnnex {
+  fn new(isolate: &mut Isolate) -> Self {
+    Self {
+      isolate,
+      mutex: Mutex::new(()),
+    }
+  }
+}
+
+#[derive(Clone)]
+pub struct IsolateHandle(Arc<IsolateAnnex>);
+
+unsafe impl Send for IsolateHandle {}
+unsafe impl Sync for IsolateHandle {}
+
+impl IsolateHandle {
+  // This function is marked unsafe because it must be called only with either
+  // IsolateAnnex::mutex locked, or from the main thread associated with the V8
+  // isolate.
+  pub(crate) unsafe fn get_isolate_ptr(&self) -> *mut Isolate {
+    self.0.isolate
+  }
+
+  fn dispose(isolate: &mut Isolate) {
+    let annex_ptr = isolate.get_data(0) as *mut IsolateAnnex;
+    if !annex_ptr.is_null() {
+      unsafe {
+        isolate.set_data(0, null_mut());
+        let _lock = (*annex_ptr).mutex.lock().unwrap();
+        let isolate_ptr = replace(&mut (*annex_ptr).isolate, null_mut());
+        assert_eq!(isolate as *mut _, isolate_ptr);
+        Arc::from_raw(annex_ptr);
+      };
+    }
+  }
+
+  pub(crate) fn new(isolate: &mut Isolate) -> Self {
+    let annex_ptr = isolate.get_data(0) as *mut IsolateAnnex;
+    if annex_ptr.is_null() {
+      let annex_arc = Arc::new(IsolateAnnex::new(isolate));
+      let annex_ptr = Arc::into_raw(annex_arc.clone());
+      unsafe {
+        isolate.set_data(0, annex_ptr as *mut c_void);
+      }
+      IsolateHandle(annex_arc)
+    } else {
+      let annex_arc = unsafe { Arc::from_raw(annex_ptr) };
+      Arc::into_raw(annex_arc.clone());
+      IsolateHandle(annex_arc)
+    }
+  }
+
   /// Forcefully terminate the current thread of JavaScript execution
   /// in the given isolate.
   ///
   /// This method can be used by any thread even if that thread has not
   /// acquired the V8 lock with a Locker object.
-  pub fn terminate_execution(&self) {
-    unsafe { v8__Isolate__TerminateExecution(self) }
-  }
-
-  /// Is V8 terminating JavaScript execution.
   ///
-  /// Returns true if JavaScript execution is currently terminating
-  /// because of a call to TerminateExecution.  In that case there are
-  /// still JavaScript frames on the stack and the termination
-  /// exception is still active.
-  pub fn is_execution_terminating(&self) -> bool {
-    unsafe { v8__Isolate__IsExecutionTerminating(self) }
+  /// Returns false if Isolate was already destroyed.
+  pub fn terminate_execution(&self) -> bool {
+    let _lock = self.0.mutex.lock().unwrap();
+    if self.0.isolate.is_null() {
+      false
+    } else {
+      unsafe { v8__Isolate__TerminateExecution(self.0.isolate) };
+      true
+    }
   }
 
   /// Resume execution capability in the given isolate, whose execution
@@ -314,19 +397,33 @@ impl Isolate {
   ///
   /// This method can be used by any thread even if that thread has not
   /// acquired the V8 lock with a Locker object.
-  pub fn cancel_terminate_execution(&self) {
-    unsafe { v8__Isolate__CancelTerminateExecution(self) }
+  ///
+  /// Returns false if Isolate was already destroyed.
+  pub fn cancel_terminate_execution(&self) -> bool {
+    let _lock = self.0.mutex.lock().unwrap();
+    if self.0.isolate.is_null() {
+      false
+    } else {
+      unsafe { v8__Isolate__CancelTerminateExecution(self.0.isolate) };
+      true
+    }
   }
 
-  /// Runs the default MicrotaskQueue until it gets empty.
-  /// Any exceptions thrown by microtask callbacks are swallowed.
-  pub fn run_microtasks(&mut self) {
-    unsafe { v8__Isolate__RunMicrotasks(self) }
-  }
-
-  /// Enqueues the callback to the default MicrotaskQueue
-  pub fn enqueue_microtask(&mut self, microtask: Local<Function>) {
-    unsafe { v8__Isolate__EnqueueMicrotask(self, microtask) }
+  /// Is V8 terminating JavaScript execution.
+  ///
+  /// Returns true if JavaScript execution is currently terminating
+  /// because of a call to TerminateExecution.  In that case there are
+  /// still JavaScript frames on the stack and the termination
+  /// exception is still active.
+  ///
+  /// Returns false if Isolate was already destroyed.
+  pub fn is_execution_terminating(&self) -> bool {
+    let _lock = self.0.mutex.lock().unwrap();
+    if self.0.isolate.is_null() {
+      false
+    } else {
+      unsafe { v8__Isolate__IsExecutionTerminating(self.0.isolate) }
+    }
   }
 
   /// Request V8 to interrupt long running JavaScript code and invoke
@@ -335,6 +432,8 @@ impl Isolate {
   /// There may be a number of interrupt requests in flight.
   /// Can be called from another thread without acquiring a |Locker|.
   /// Registered |callback| must not reenter interrupted Isolate.
+  ///
+  /// Returns false if Isolate was already destroyed.
   // Clippy warns that this method is dereferencing a raw pointer, but it is
   // not: https://github.com/rust-lang/rust-clippy/issues/3045
   #[allow(clippy::not_unsafe_ptr_arg_deref)]
@@ -342,19 +441,21 @@ impl Isolate {
     &self,
     callback: InterruptCallback,
     data: *mut c_void,
-  ) {
-    unsafe { v8__Isolate__RequestInterrupt(self, callback, data) }
-  }
-
-  /// Disposes the isolate.  The isolate must not be entered by any
-  /// thread to be disposable.
-  pub unsafe fn dispose(&mut self) {
-    v8__Isolate__Dispose(self)
+  ) -> bool {
+    let _lock = self.0.mutex.lock().unwrap();
+    if self.0.isolate.is_null() {
+      false
+    } else {
+      unsafe { v8__Isolate__RequestInterrupt(self.0.isolate, callback, data) };
+      true
+    }
   }
 }
 
 /// Internal method for constructing an OwnedIsolate.
-pub unsafe fn new_owned_isolate(isolate_ptr: *mut Isolate) -> OwnedIsolate {
+pub(crate) unsafe fn new_owned_isolate(
+  isolate_ptr: *mut Isolate,
+) -> OwnedIsolate {
   OwnedIsolate(NonNull::new(isolate_ptr).unwrap())
 }
 

src/lib.rs

@@ -132,6 +132,7 @@ pub use isolate::CreateParams;
 pub use isolate::HostImportModuleDynamicallyCallback;
 pub use isolate::HostInitializeImportMetaObjectCallback;
 pub use isolate::Isolate;
+pub use isolate::IsolateHandle;
 pub use isolate::MessageCallback;
 pub use isolate::OwnedIsolate;
 pub use isolate::PromiseRejectCallback;

tests/test_api.rs

@@ -126,6 +126,28 @@ fn global_handles() {
   assert!(g5.is_empty());
 }
 
+#[test]
+fn global_handle_drop() {
+  let _setup_guard = setup();
+
+  // Global 'g1' will be dropped _after_ the Isolate has been disposed.
+  let mut g1 = v8::Global::<v8::String>::new();
+
+  let mut params = v8::Isolate::create_params();
+  params.set_array_buffer_allocator(v8::new_default_allocator());
+  let mut isolate = v8::Isolate::new(params);
+
+  let mut hs = v8::HandleScope::new(&mut isolate);
+  let scope = hs.enter();
+
+  let l1 = v8::String::new(scope, "foo").unwrap();
+  g1.set(scope, l1);
+
+  // Global 'g2' will be dropped _before_ the Isolate has been disposed.
+  let l2 = v8::String::new(scope, "bar").unwrap();
+  let _g2 = v8::Global::new_from(scope, l2);
+}
+
 #[test]
 fn test_string() {
   let _setup_guard = setup();
@@ -451,12 +473,47 @@ fn throw_exception() {
   }
 }
 
+#[test]
+fn thread_safe_handle_drop_after_isolate() {
+  let _setup_guard = setup();
+  let mut params = v8::Isolate::create_params();
+  params.set_array_buffer_allocator(v8::new_default_allocator());
+  let mut isolate = v8::Isolate::new(params);
+  let handle = isolate.thread_safe_handle();
+  // We can call it twice.
+  let handle_ = isolate.thread_safe_handle();
+  // Check that handle is Send and Sync.
+  fn f<S: Send + Sync>(_: S) {}
+  f(handle_);
+  // All methods on IsolateHandle should return false after the isolate is
+  // dropped.
+  drop(isolate);
+  assert_eq!(false, handle.terminate_execution());
+  assert_eq!(false, handle.cancel_terminate_execution());
+  assert_eq!(false, handle.is_execution_terminating());
+  static CALL_COUNT: AtomicUsize = AtomicUsize::new(0);
+  extern "C" fn callback(
+    _isolate: &mut v8::Isolate,
+    data: *mut std::ffi::c_void,
+  ) {
+    assert_eq!(data, std::ptr::null_mut());
+    CALL_COUNT.fetch_add(1, Ordering::SeqCst);
+  }
+  assert_eq!(
+    false,
+    handle.request_interrupt(callback, std::ptr::null_mut())
+  );
+  assert_eq!(CALL_COUNT.load(Ordering::SeqCst), 0);
+}
+
+// TODO(ry) This test should use threads
 #[test]
 fn terminate_execution() {
   let _setup_guard = setup();
   let mut params = v8::Isolate::create_params();
   params.set_array_buffer_allocator(v8::new_default_allocator());
   let mut isolate = v8::Isolate::new(params);
+  let handle = isolate.thread_safe_handle();
   // Originally run fine.
   {
     let mut hs = v8::HandleScope::new(&mut isolate);
@@ -469,7 +526,7 @@ fn terminate_execution() {
     assert!(result.same_value(true_val));
   }
   // Terminate.
-  isolate.terminate_execution();
+  handle.terminate_execution();
   // Below run should fail with terminated knowledge.
   {
     let mut hs = v8::HandleScope::new(&mut isolate);
@@ -484,7 +541,7 @@ fn terminate_execution() {
     assert!(tc.has_terminated());
   }
   // Cancel termination.
-  isolate.cancel_terminate_execution();
+  handle.cancel_terminate_execution();
   // Works again.
   {
     let mut hs = v8::HandleScope::new(&mut isolate);
@@ -498,12 +555,14 @@ fn terminate_execution() {
   }
 }
 
+// TODO(ry) This test should use threads
 #[test]
 fn request_interrupt_small_scripts() {
   let _setup_guard = setup();
   let mut params = v8::Isolate::create_params();
   params.set_array_buffer_allocator(v8::new_default_allocator());
   let mut isolate = v8::Isolate::new(params);
+  let handle = isolate.thread_safe_handle();
   {
     let mut hs = v8::HandleScope::new(&mut isolate);
     let scope = hs.enter();
@@ -519,9 +578,7 @@ fn request_interrupt_small_scripts() {
       assert_eq!(data, std::ptr::null_mut());
       CALL_COUNT.fetch_add(1, Ordering::SeqCst);
     }
-    scope
-      .isolate()
-      .request_interrupt(callback, std::ptr::null_mut());
+    handle.request_interrupt(callback, std::ptr::null_mut());
     eval(scope, context, "(function(x){return x;})(1);");
     assert_eq!(CALL_COUNT.load(Ordering::SeqCst), 1);
   }