chore: Don't store Global<Context> in callback info

Callbacks (runOnMainThread, frame, and timer) can run in the context in
which they were created, which we can get via GetCreationContext(). So,
there is no need to store a v8::Global<v8::Context> in which to invoke
the callback.

See v8/v8@b38bf5b0 for why it's OK to use
ToLocalChecked() - the creation context is only null if the objects
were created in WASM instead of JS.

Author: ptomato

test-app/runtime/src/main/cpp/CallbackHandlers.cpp

@@ -667,13 +667,11 @@ void CallbackHandlers::RunOnMainThreadCallback(const FunctionCallbackInfo<v8::Va
     Isolate::Scope isolate_scope(isolate);
     HandleScope handle_scope(isolate);
 
-    Local<Context> context = isolate->GetCurrentContext();
-
     uint64_t key = ++count_;
     Local<v8::Function> callback = args[0].As<v8::Function>();
 
     bool inserted;
-    std::tie(std::ignore, inserted) = cache_.try_emplace(key, isolate, callback, context);
+    std::tie(std::ignore, inserted) = cache_.try_emplace(key, isolate, callback);
     assert(inserted && "Main thread callback ID should not be duplicated");
 
     auto value = Callback(key);
@@ -697,9 +695,9 @@ int CallbackHandlers::RunOnMainThreadFdCallback(int fd, int events, void *data)
     v8::Locker locker(isolate);
     Isolate::Scope isolate_scope(isolate);
     HandleScope handle_scope(isolate);
-    auto context = it->second.context_.Get(isolate);
-    Context::Scope context_scope(context);
     Local<v8::Function> cb = it->second.callback_.Get(isolate);
+    v8::Local<v8::Context> context = cb->GetCreationContextChecked();
+    Context::Scope context_scope(context);
 
     v8::TryCatch tc(isolate);
 
@@ -1655,7 +1653,7 @@ void CallbackHandlers::PostFrameCallback(const FunctionCallbackInfo<v8::Value> &
 
         robin_hood::unordered_map<uint64_t, FrameCallbackCacheEntry>::iterator val;
         bool inserted;
-        std::tie(val, inserted) = frameCallbackCache_.try_emplace(key, isolate, callback, context, key);
+        std::tie(val, inserted) = frameCallbackCache_.try_emplace(key, isolate, callback, key);
         assert(inserted && "Frame callback ID should not be duplicated");
 
         PostCallback(args, &val->second, context);
@@ -1757,4 +1755,4 @@ jmethodID CallbackHandlers::INIT_WORKER_METHOD_ID = nullptr;
 
 NumericCasts CallbackHandlers::castFunctions;
 ArrayElementAccessor CallbackHandlers::arrayElementAccessor;
-FieldAccessor CallbackHandlers::fieldAccessor;
+FieldAccessor CallbackHandlers::fieldAccessor;

test-app/runtime/src/main/cpp/CallbackHandlers.h

@@ -297,20 +297,17 @@ namespace tns {
 
 
         struct CacheEntry {
-            CacheEntry(v8::Isolate* isolate, v8::Local<v8::Function> callback, v8::Local<v8::Context> context)
+            CacheEntry(v8::Isolate* isolate, v8::Local<v8::Function> callback)
                     : isolate_(isolate),
-                      callback_(isolate, callback),
-                      context_(isolate, context){
+                      callback_(isolate, callback) {
             }
 
             ~CacheEntry() {
-                context_.Reset();
                 callback_.Reset();
             }
 
             v8::Isolate* isolate_;
             v8::Global<v8::Function> callback_;
-            v8::Global<v8::Context> context_;
         };
 
         static robin_hood::unordered_map<uint64_t, CacheEntry> cache_;
@@ -319,22 +316,18 @@ namespace tns {
         static std::atomic_uint64_t frameCallbackCount_;
 
         struct FrameCallbackCacheEntry {
-            FrameCallbackCacheEntry(v8::Isolate *isolate, v8::Local<v8::Function> callback,
-                                    v8::Local<v8::Context> context, uint64_t aId)
+            FrameCallbackCacheEntry(v8::Isolate *isolate, v8::Local<v8::Function> callback, uint64_t aId)
                 : isolate_(isolate),
                   callback_(isolate, callback),
-                  context_(isolate, context),
                   id(aId) {
             }
 
             ~FrameCallbackCacheEntry() {
-                context_.Reset();
                 callback_.Reset();
             }
 
             v8::Isolate *isolate_;
             v8::Global<v8::Function> callback_;
-            v8::Global<v8::Context> context_;
             bool removed = false;
             uint64_t id;
 
@@ -358,10 +351,10 @@ namespace tns {
                     v8::Locker locker(isolate);
                     v8::Isolate::Scope isolate_scope(isolate);
                     v8::HandleScope handle_scope(isolate);
-                    auto context = entry->context_.Get(isolate);
+                    v8::Local<v8::Function> cb = entry->callback_.Get(isolate);
+                    v8::Local<v8::Context> context = cb->GetCreationContextChecked();
                     v8::Context::Scope context_scope(context);
 
-                    v8::Local<v8::Function> cb = entry->callback_.Get(isolate);
                     v8::Local<v8::Value> args[1] = {v8::Number::New(isolate, ts)};
 
                     v8::TryCatch tc(isolate);

test-app/runtime/src/main/cpp/Timers.cpp

@@ -293,7 +293,8 @@ int Timers::PumpTimerLoopCallback(int fd, int events, void *data) {
             task->startTime_ = task->dueTime_;
             thiz->addTask(task);
         }
-        auto context = task->context_.Get(isolate);
+        v8::Local<v8::Function> cb = task->callback_.Get(isolate);
+        v8::Local<v8::Context> context = cb->GetCreationContextChecked();
         Context::Scope context_scope(context);
         TryCatch tc(isolate);
         auto argc = task->args_.get() == nullptr ? 0 : task->args_->size();
@@ -302,9 +303,9 @@ int Timers::PumpTimerLoopCallback(int fd, int events, void *data) {
             for (int i = 0; i < argc; i++) {
                 argv[i] = task->args_->at(i)->Get(isolate);
             }
-            task->callback_.Get(isolate)->Call(context, context->Global(), argc, argv);
+            cb->Call(context, context->Global(), argc, argv);
         } else {
-            task->callback_.Get(isolate)->Call(context, context->Global(), 0, nullptr);
+            cb->Call(context, context->Global(), 0, nullptr);
         }
         // task is not queued, so it's either a setTimeout or a cleared setInterval
         // ensure we remove it

test-app/runtime/src/main/cpp/Timers.h

@@ -20,7 +20,7 @@ namespace tns {
                          bool repeats,
                          const std::shared_ptr<std::vector<std::shared_ptr<v8::Persistent<v8::Value>>>> &args,
                          int id, double startTime)
-                : isolate_(isolate), context_(isolate, context), callback_(isolate, callback),
+                : isolate_(isolate), callback_(isolate, callback),
                   frequency_(frequency), repeats_(repeats), args_(args), id_(id),
                   startTime_(startTime) {
 
@@ -36,7 +36,6 @@ namespace tns {
         }
 
         inline void Unschedule() {
-            context_.Reset();
             callback_.Reset();
             args_.reset();
             isolate_ = nullptr;
@@ -46,7 +45,6 @@ namespace tns {
 
         int nestingLevel_ = 0;
         v8::Isolate *isolate_;
-        v8::Persistent<v8::Context> context_;
         v8::Persistent<v8::Function> callback_;
         std::shared_ptr<std::vector<std::shared_ptr<v8::Persistent<v8::Value>>>> args_;
         bool repeats_ = false;