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#ifndef CALLBACK_BRIDGE_H
#define CALLBACK_BRIDGE_H
#include <vector>
#include <nan.h>
#include <algorithm>
#include <uv.h>
#define COMMA ,
template <typename T, typename L = void*>
class CallbackBridge {
public:
CallbackBridge(v8::Local<v8::Function>, bool);
virtual ~CallbackBridge();
// Executes the callback
T operator()(std::vector<void*>);
protected:
// We will expose a bridge object to the JS callback that wraps this instance so we don't loose context.
// This is the V8 constructor for such objects.
static Nan::MaybeLocal<v8::Function> get_wrapper_constructor();
static void async_gone(uv_handle_t *handle);
static NAN_METHOD(New);
static NAN_METHOD(ReturnCallback);
static Nan::Persistent<v8::Function> wrapper_constructor;
Nan::Persistent<v8::Object> wrapper;
// The callback that will get called in the main thread after the worker thread used for the sass
// compilation step makes a call to uv_async_send()
static void dispatched_async_uv_callback(uv_async_t*);
// The V8 values sent to our ReturnCallback must be read on the main thread not the sass worker thread.
// This gives a chance to specialized subclasses to transform those values into whatever makes sense to
// sass before we resume the worker thread.
virtual T post_process_return_value(v8::Local<v8::Value>) const =0;
virtual std::vector<v8::Local<v8::Value>> pre_process_args(std::vector<L>) const =0;
Nan::Callback* callback;
Nan::AsyncResource* async_resource;
bool is_sync;
uv_mutex_t cv_mutex;
uv_cond_t condition_variable;
uv_async_t *async;
std::vector<L> argv;
bool has_returned;
T return_value;
};
template <typename T, typename L>
Nan::Persistent<v8::Function> CallbackBridge<T, L>::wrapper_constructor;
template <typename T, typename L>
CallbackBridge<T, L>::CallbackBridge(v8::Local<v8::Function> callback, bool is_sync) : callback(new Nan::Callback(callback)), is_sync(is_sync) {
/*
* This is invoked from the main JavaScript thread.
* V8 context is available.
*/
Nan::HandleScope scope;
uv_mutex_init(&this->cv_mutex);
uv_cond_init(&this->condition_variable);
if (!is_sync) {
this->async = new uv_async_t;
this->async->data = (void*) this;
uv_async_init(uv_default_loop(), this->async, (uv_async_cb) dispatched_async_uv_callback);
this->async_resource = new Nan::AsyncResource("node-sass:CallbackBridge");
}
v8::Local<v8::Function> func = CallbackBridge<T, L>::get_wrapper_constructor().ToLocalChecked();
wrapper.Reset(Nan::NewInstance(func).ToLocalChecked());
Nan::SetInternalFieldPointer(Nan::New(wrapper), 0, this);
}
template <typename T, typename L>
CallbackBridge<T, L>::~CallbackBridge() {
delete this->callback;
this->wrapper.Reset();
uv_cond_destroy(&this->condition_variable);
uv_mutex_destroy(&this->cv_mutex);
if (!is_sync) {
uv_close((uv_handle_t*)this->async, &async_gone);
delete this->async_resource;
}
}
template <typename T, typename L>
T CallbackBridge<T, L>::operator()(std::vector<void*> argv) {
// argv.push_back(wrapper);
if (this->is_sync) {
/*
* This is invoked from the main JavaScript thread.
* V8 context is available.
*
* Establish Local<> scope for all functions
* from types invoked by pre_process_args() and
* post_process_args().
*/
Nan::HandleScope scope;
Nan::TryCatch try_catch;
std::vector<v8::Local<v8::Value>> argv_v8 = pre_process_args(argv);
if (try_catch.HasCaught()) {
Nan::FatalException(try_catch);
}
argv_v8.push_back(Nan::New(wrapper));
return this->post_process_return_value(
Nan::Call(*this->callback, argv_v8.size(), &argv_v8[0]).ToLocalChecked()
);
} else {
/*
* This is invoked from the worker thread.
* No V8 context and functions available.
* Just wait for response from asynchronously
* scheduled JavaScript code
*
* XXX Issue #1048: We block here even if the
* event loop stops and the callback
* would never be executed.
* XXX Issue #857: By waiting here we occupy
* one of the threads taken from the
* uv threadpool. Might deadlock if
* async I/O executed from JavaScript callbacks.
*/
this->argv = argv;
uv_mutex_lock(&this->cv_mutex);
this->has_returned = false;
uv_async_send(this->async);
while (!this->has_returned) {
uv_cond_wait(&this->condition_variable, &this->cv_mutex);
}
uv_mutex_unlock(&this->cv_mutex);
return this->return_value;
}
}
template <typename T, typename L>
void CallbackBridge<T, L>::dispatched_async_uv_callback(uv_async_t *req) {
CallbackBridge* bridge = static_cast<CallbackBridge*>(req->data);
/*
* Function scheduled via uv_async mechanism, therefore
* it is invoked from the main JavaScript thread.
* V8 context is available.
*
* Establish Local<> scope for all functions
* from types invoked by pre_process_args() and
* post_process_args().
*/
Nan::HandleScope scope;
Nan::TryCatch try_catch;
std::vector<v8::Local<v8::Value>> argv_v8 = bridge->pre_process_args(bridge->argv);
if (try_catch.HasCaught()) {
Nan::FatalException(try_catch);
}
argv_v8.push_back(Nan::New(bridge->wrapper));
bridge->callback->Call(argv_v8.size(), &argv_v8[0], bridge->async_resource);
if (try_catch.HasCaught()) {
Nan::FatalException(try_catch);
}
}
template <typename T, typename L>
NAN_METHOD(CallbackBridge<T COMMA L>::ReturnCallback) {
/*
* Callback function invoked by the user code.
* It is invoked from the main JavaScript thread.
* V8 context is available.
*
* Implicit Local<> handle scope created by NAN_METHOD(.)
*/
CallbackBridge<T, L>* bridge = static_cast<CallbackBridge<T, L>*>(Nan::GetInternalFieldPointer(info.This(), 0));
Nan::TryCatch try_catch;
bridge->return_value = bridge->post_process_return_value(info[0]);
{
uv_mutex_lock(&bridge->cv_mutex);
bridge->has_returned = true;
uv_mutex_unlock(&bridge->cv_mutex);
}
uv_cond_broadcast(&bridge->condition_variable);
if (try_catch.HasCaught()) {
Nan::FatalException(try_catch);
}
}
template <typename T, typename L>
Nan::MaybeLocal<v8::Function> CallbackBridge<T, L>::get_wrapper_constructor() {
/* Uses handle scope created in the CallbackBridge<T, L> constructor */
if (wrapper_constructor.IsEmpty()) {
v8::Local<v8::FunctionTemplate> tpl = Nan::New<v8::FunctionTemplate>(New);
tpl->SetClassName(Nan::New("CallbackBridge").ToLocalChecked());
tpl->InstanceTemplate()->SetInternalFieldCount(1);
Nan::SetPrototypeTemplate(tpl, "success",
Nan::New<v8::FunctionTemplate>(ReturnCallback)
);
wrapper_constructor.Reset(Nan::GetFunction(tpl).ToLocalChecked());
}
return Nan::New(wrapper_constructor);
}
template <typename T, typename L>
NAN_METHOD(CallbackBridge<T COMMA L>::New) {
info.GetReturnValue().Set(info.This());
}
template <typename T, typename L>
void CallbackBridge<T, L>::async_gone(uv_handle_t *handle) {
delete (uv_async_t *)handle;
}
#endif
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