[wasm-c-api] Drop Isolate::Enter/Exit calls...

...from the Store constructor/destructor. They were preventing embedders
from using several Stores with overlapping but non-nested lifetimes.
Without Isolate::Enter, such use cases are supported; the only consequence
is that Isolate::Current will not work and therefore must not be called;
but it is deprecated and not called from the Wasm C API anyway.

Change-Id: I65eda00243126e189febb0fd8b38a953c4ee078f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1698387
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62692}

src/wasm/c-api.cc

@@ -269,7 +269,6 @@ StoreImpl::~StoreImpl() {
       v8::kGCCallbackFlagForced);
 #endif
   context()->Exit();
-  isolate_->Exit();
   isolate_->Dispose();
   delete create_params_.array_buffer_allocator;
 }
@@ -294,7 +293,6 @@ auto Store::make(Engine*) -> own<Store*> {
   if (!isolate) return own<Store*>();
 
   {
-    v8::Isolate::Scope isolate_scope(isolate);
     v8::HandleScope handle_scope(isolate);
 
     // Create context.
@@ -305,8 +303,10 @@ auto Store::make(Engine*) -> own<Store*> {
     store->isolate_ = isolate;
     store->context_ = v8::Eternal<v8::Context>(isolate, context);
   }
-
-  store->isolate()->Enter();
+  // We intentionally do not call isolate->Enter() here, because that would
+  // prevent embedders from using stores with overlapping but non-nested
+  // lifetimes. The consequence is that Isolate::Current() is dysfunctional
+  // and hence must not be called by anything reachable via this file.
   store->context()->Enter();
   isolate->SetData(0, store.get());
 

test/wasm-api-tests/threads.cc

@@ -90,6 +90,16 @@ TEST_F(WasmCapiTest, Threads) {
   EXPECT_EQ(kExpected, g_traces);
 }
 
+TEST_F(WasmCapiTest, MultiStoresOneThread) {
+  // These Stores intentionally have overlapping, but non-nested lifetimes.
+  own<Store*> store1 = Store::make(engine());
+  own<Store*> store2 = Store::make(engine());
+  own<Store*> store3 = Store::make(engine());
+  store1.reset();
+  store2.reset();
+  store3.reset();
+}
+
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8