environment.cc

#include "node.h"
#include "node_context_data.h"
#include "node_errors.h"
#include "node_internals.h"
#include "node_native_module_env.h"
#include "node_platform.h"
#include "node_v8_platform-inl.h"
#include "uv.h"

#if HAVE_INSPECTOR
#include "inspector/worker_inspector.h"  // ParentInspectorHandle
#endif

namespace node {
using errors::TryCatchScope;
using v8::Array;
using v8::Context;
using v8::EscapableHandleScope;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::MaybeLocal;
using v8::Null;
using v8::Object;
using v8::ObjectTemplate;
using v8::Private;
using v8::PropertyDescriptor;
using v8::SealHandleScope;
using v8::String;
using v8::Value;

static bool AllowWasmCodeGenerationCallback(Local<Context> context,
                                            Local<String>) {
  Local<Value> wasm_code_gen =
      context->GetEmbedderData(ContextEmbedderIndex::kAllowWasmCodeGeneration);
  return wasm_code_gen->IsUndefined() || wasm_code_gen->IsTrue();
}

static bool ShouldAbortOnUncaughtException(Isolate* isolate) {
  DebugSealHandleScope scope(isolate);
  Environment* env = Environment::GetCurrent(isolate);
  return env != nullptr &&
         (env->is_main_thread() || !env->is_stopping()) &&
         env->abort_on_uncaught_exception() &&
         env->should_abort_on_uncaught_toggle()[0] &&
         !env->inside_should_not_abort_on_uncaught_scope();
}

static MaybeLocal<Value> PrepareStackTraceCallback(Local<Context> context,
                                      Local<Value> exception,
                                      Local<Array> trace) {
  Environment* env = Environment::GetCurrent(context);
  if (env == nullptr) {
    return exception->ToString(context).FromMaybe(Local<Value>());
  }
  Local<Function> prepare = env->prepare_stack_trace_callback();
  if (prepare.IsEmpty()) {
    return exception->ToString(context).FromMaybe(Local<Value>());
  }
  Local<Value> args[] = {
      context->Global(),
      exception,
      trace,
  };
  // This TryCatch + Rethrow is required by V8 due to details around exception
  // handling there. For C++ callbacks, V8 expects a scheduled exception (which
  // is what ReThrow gives us). Just returning the empty MaybeLocal would leave
  // us with a pending exception.
  TryCatchScope try_catch(env);
  MaybeLocal<Value> result = prepare->Call(
      context, Undefined(env->isolate()), arraysize(args), args);
  if (try_catch.HasCaught() && !try_catch.HasTerminated()) {
    try_catch.ReThrow();
  }
  return result;
}

void* NodeArrayBufferAllocator::Allocate(size_t size) {
  void* ret;
  if (zero_fill_field_ || per_process::cli_options->zero_fill_all_buffers)
    ret = UncheckedCalloc(size);
  else
    ret = UncheckedMalloc(size);
  if (LIKELY(ret != nullptr))
    total_mem_usage_.fetch_add(size, std::memory_order_relaxed);
  return ret;
}

void* NodeArrayBufferAllocator::AllocateUninitialized(size_t size) {
  void* ret = node::UncheckedMalloc(size);
  if (LIKELY(ret != nullptr))
    total_mem_usage_.fetch_add(size, std::memory_order_relaxed);
  return ret;
}

void* NodeArrayBufferAllocator::Reallocate(
    void* data, size_t old_size, size_t size) {
  void* ret = UncheckedRealloc<char>(static_cast<char*>(data), size);
  if (LIKELY(ret != nullptr) || UNLIKELY(size == 0))
    total_mem_usage_.fetch_add(size - old_size, std::memory_order_relaxed);
  return ret;
}

void NodeArrayBufferAllocator::Free(void* data, size_t size) {
  total_mem_usage_.fetch_sub(size, std::memory_order_relaxed);
  free(data);
}

DebuggingArrayBufferAllocator::~DebuggingArrayBufferAllocator() {
  CHECK(allocations_.empty());
}

void* DebuggingArrayBufferAllocator::Allocate(size_t size) {
  Mutex::ScopedLock lock(mutex_);
  void* data = NodeArrayBufferAllocator::Allocate(size);
  RegisterPointerInternal(data, size);
  return data;
}

void* DebuggingArrayBufferAllocator::AllocateUninitialized(size_t size) {
  Mutex::ScopedLock lock(mutex_);
  void* data = NodeArrayBufferAllocator::AllocateUninitialized(size);
  RegisterPointerInternal(data, size);
  return data;
}

void DebuggingArrayBufferAllocator::Free(void* data, size_t size) {
  Mutex::ScopedLock lock(mutex_);
  UnregisterPointerInternal(data, size);
  NodeArrayBufferAllocator::Free(data, size);
}

void* DebuggingArrayBufferAllocator::Reallocate(void* data,
                                                size_t old_size,
                                                size_t size) {
  Mutex::ScopedLock lock(mutex_);
  void* ret = NodeArrayBufferAllocator::Reallocate(data, old_size, size);
  if (ret == nullptr) {
    if (size == 0)  // i.e. equivalent to free().
      UnregisterPointerInternal(data, old_size);
    return nullptr;
  }

  if (data != nullptr) {
    auto it = allocations_.find(data);
    CHECK_NE(it, allocations_.end());
    allocations_.erase(it);
  }

  RegisterPointerInternal(ret, size);
  return ret;
}

void DebuggingArrayBufferAllocator::RegisterPointer(void* data, size_t size) {
  Mutex::ScopedLock lock(mutex_);
  NodeArrayBufferAllocator::RegisterPointer(data, size);
  RegisterPointerInternal(data, size);
}

void DebuggingArrayBufferAllocator::UnregisterPointer(void* data, size_t size) {
  Mutex::ScopedLock lock(mutex_);
  NodeArrayBufferAllocator::UnregisterPointer(data, size);
  UnregisterPointerInternal(data, size);
}

void DebuggingArrayBufferAllocator::UnregisterPointerInternal(void* data,
                                                              size_t size) {
  if (data == nullptr) return;
  auto it = allocations_.find(data);
  CHECK_NE(it, allocations_.end());
  if (size > 0) {
    // We allow allocations with size 1 for 0-length buffers to avoid having
    // to deal with nullptr values.
    CHECK_EQ(it->second, size);
  }
  allocations_.erase(it);
}

void DebuggingArrayBufferAllocator::RegisterPointerInternal(void* data,
                                                            size_t size) {
  if (data == nullptr) return;
  CHECK_EQ(allocations_.count(data), 0);
  allocations_[data] = size;
}

std::unique_ptr<ArrayBufferAllocator> ArrayBufferAllocator::Create(bool debug) {
  if (debug || per_process::cli_options->debug_arraybuffer_allocations)
    return std::make_unique<DebuggingArrayBufferAllocator>();
  else
    return std::make_unique<NodeArrayBufferAllocator>();
}

ArrayBufferAllocator* CreateArrayBufferAllocator() {
  return ArrayBufferAllocator::Create().release();
}

void FreeArrayBufferAllocator(ArrayBufferAllocator* allocator) {
  delete allocator;
}

void SetIsolateCreateParamsForNode(Isolate::CreateParams* params) {
  const uint64_t constrained_memory = uv_get_constrained_memory();
  const uint64_t total_memory = constrained_memory > 0 ?
      std::min(uv_get_total_memory(), constrained_memory) :
      uv_get_total_memory();
  if (total_memory > 0) {
    // V8 defaults to 700MB or 1.4GB on 32 and 64 bit platforms respectively.
    // This default is based on browser use-cases. Tell V8 to configure the
    // heap based on the actual physical memory.
    params->constraints.ConfigureDefaults(total_memory, 0);
  }
  params->embedder_wrapper_object_index = BaseObject::InternalFields::kSlot;
  params->embedder_wrapper_type_index = std::numeric_limits<int>::max();
}

void SetIsolateErrorHandlers(v8::Isolate* isolate, const IsolateSettings& s) {
  if (s.flags & MESSAGE_LISTENER_WITH_ERROR_LEVEL)
    isolate->AddMessageListenerWithErrorLevel(
            errors::PerIsolateMessageListener,
            Isolate::MessageErrorLevel::kMessageError |
                Isolate::MessageErrorLevel::kMessageWarning);

  auto* abort_callback = s.should_abort_on_uncaught_exception_callback ?
      s.should_abort_on_uncaught_exception_callback :
      ShouldAbortOnUncaughtException;
  isolate->SetAbortOnUncaughtExceptionCallback(abort_callback);

  auto* fatal_error_cb = s.fatal_error_callback ?
      s.fatal_error_callback : OnFatalError;
  isolate->SetFatalErrorHandler(fatal_error_cb);

  auto* prepare_stack_trace_cb = s.prepare_stack_trace_callback ?
      s.prepare_stack_trace_callback : PrepareStackTraceCallback;
  isolate->SetPrepareStackTraceCallback(prepare_stack_trace_cb);
}

void SetIsolateMiscHandlers(v8::Isolate* isolate, const IsolateSettings& s) {
  isolate->SetMicrotasksPolicy(s.policy);

  auto* allow_wasm_codegen_cb = s.allow_wasm_code_generation_callback ?
    s.allow_wasm_code_generation_callback : AllowWasmCodeGenerationCallback;
  isolate->SetAllowWasmCodeGenerationCallback(allow_wasm_codegen_cb);

  if ((s.flags & SHOULD_NOT_SET_PROMISE_REJECTION_CALLBACK) == 0) {
    auto* promise_reject_cb = s.promise_reject_callback ?
      s.promise_reject_callback : task_queue::PromiseRejectCallback;
    isolate->SetPromiseRejectCallback(promise_reject_cb);
  }

  if (s.flags & DETAILED_SOURCE_POSITIONS_FOR_PROFILING)
    v8::CpuProfiler::UseDetailedSourcePositionsForProfiling(isolate);
}

void SetIsolateUpForNode(v8::Isolate* isolate,
                         const IsolateSettings& settings) {
  SetIsolateErrorHandlers(isolate, settings);
  SetIsolateMiscHandlers(isolate, settings);
}

void SetIsolateUpForNode(v8::Isolate* isolate) {
  IsolateSettings settings;
  SetIsolateUpForNode(isolate, settings);
}

Isolate* NewIsolate(ArrayBufferAllocator* allocator, uv_loop_t* event_loop) {
  return NewIsolate(allocator, event_loop, GetMainThreadMultiIsolatePlatform());
}

// TODO(joyeecheung): we may want to expose this, but then we need to be
// careful about what we override in the params.
Isolate* NewIsolate(Isolate::CreateParams* params,
                    uv_loop_t* event_loop,
                    MultiIsolatePlatform* platform) {
  Isolate* isolate = Isolate::Allocate();
  if (isolate == nullptr) return nullptr;

  // Register the isolate on the platform before the isolate gets initialized,
  // so that the isolate can access the platform during initialization.
  platform->RegisterIsolate(isolate, event_loop);

  SetIsolateCreateParamsForNode(params);
  Isolate::Initialize(isolate, *params);
  SetIsolateUpForNode(isolate);

  return isolate;
}

Isolate* NewIsolate(ArrayBufferAllocator* allocator,
                    uv_loop_t* event_loop,
                    MultiIsolatePlatform* platform) {
  Isolate::CreateParams params;
  if (allocator != nullptr) params.array_buffer_allocator = allocator;
  return NewIsolate(&params, event_loop, platform);
}

Isolate* NewIsolate(std::shared_ptr<ArrayBufferAllocator> allocator,
                    uv_loop_t* event_loop,
                    MultiIsolatePlatform* platform) {
  Isolate::CreateParams params;
  if (allocator) params.array_buffer_allocator_shared = allocator;
  return NewIsolate(&params, event_loop, platform);
}

IsolateData* CreateIsolateData(Isolate* isolate,
                               uv_loop_t* loop,
                               MultiIsolatePlatform* platform,
                               ArrayBufferAllocator* allocator) {
  return new IsolateData(isolate, loop, platform, allocator);
}

void FreeIsolateData(IsolateData* isolate_data) {
  delete isolate_data;
}

InspectorParentHandle::~InspectorParentHandle() {}

// Hide the internal handle class from the public API.
#if HAVE_INSPECTOR
struct InspectorParentHandleImpl : public InspectorParentHandle {
  std::unique_ptr<inspector::ParentInspectorHandle> impl;

  explicit InspectorParentHandleImpl(
      std::unique_ptr<inspector::ParentInspectorHandle>&& impl)
    : impl(std::move(impl)) {}
};
#endif

Environment* CreateEnvironment(IsolateData* isolate_data,
                               Local<Context> context,
                               int argc,
                               const char* const* argv,
                               int exec_argc,
                               const char* const* exec_argv) {
  return CreateEnvironment(
      isolate_data, context,
      std::vector<std::string>(argv, argv + argc),
      std::vector<std::string>(exec_argv, exec_argv + exec_argc));
}

Environment* CreateEnvironment(
    IsolateData* isolate_data,
    Local<Context> context,
    const std::vector<std::string>& args,
    const std::vector<std::string>& exec_args,
    EnvironmentFlags::Flags flags,
    ThreadId thread_id,
    std::unique_ptr<InspectorParentHandle> inspector_parent_handle) {
  Isolate* isolate = context->GetIsolate();
  HandleScope handle_scope(isolate);
  Context::Scope context_scope(context);
  // TODO(addaleax): This is a much better place for parsing per-Environment
  // options than the global parse call.
  Environment* env = new Environment(
      isolate_data, context, args, exec_args, nullptr, flags, thread_id);
#if HAVE_INSPECTOR
  if (inspector_parent_handle) {
    env->InitializeInspector(
        std::move(static_cast<InspectorParentHandleImpl*>(
            inspector_parent_handle.get())->impl));
  } else {
    env->InitializeInspector({});
  }
#endif

  if (env->RunBootstrapping().IsEmpty()) {
    FreeEnvironment(env);
    return nullptr;
  }

  return env;
}

void FreeEnvironment(Environment* env) {
  Isolate::DisallowJavascriptExecutionScope disallow_js(env->isolate(),
      Isolate::DisallowJavascriptExecutionScope::THROW_ON_FAILURE);
  {
    HandleScope handle_scope(env->isolate());  // For env->context().
    Context::Scope context_scope(env->context());
    SealHandleScope seal_handle_scope(env->isolate());

    env->set_stopping(true);
    env->stop_sub_worker_contexts();
    env->RunCleanup();
    RunAtExit(env);
  }

  // This call needs to be made while the `Environment` is still alive
  // because we assume that it is available for async tracking in the
  // NodePlatform implementation.
  MultiIsolatePlatform* platform = env->isolate_data()->platform();
  if (platform != nullptr)
    platform->DrainTasks(env->isolate());

  delete env;
}

NODE_EXTERN std::unique_ptr<InspectorParentHandle> GetInspectorParentHandle(
    Environment* env,
    ThreadId thread_id,
    const char* url) {
  CHECK_NOT_NULL(env);
  CHECK_NE(thread_id.id, static_cast<uint64_t>(-1));
#if HAVE_INSPECTOR
  return std::make_unique<InspectorParentHandleImpl>(
      env->inspector_agent()->GetParentHandle(thread_id.id, url));
#else
  return {};
#endif
}

void LoadEnvironment(Environment* env) {
  USE(LoadEnvironment(env,
                      StartExecutionCallback{},
                      {}));
}

MaybeLocal<Value> LoadEnvironment(
    Environment* env,
    StartExecutionCallback cb,
    std::unique_ptr<InspectorParentHandle> removeme) {
  env->InitializeLibuv();
  env->InitializeDiagnostics();

  return StartExecution(env, cb);
}

MaybeLocal<Value> LoadEnvironment(
    Environment* env,
    const char* main_script_source_utf8,
    std::unique_ptr<InspectorParentHandle> removeme) {
  CHECK_NOT_NULL(main_script_source_utf8);
  return LoadEnvironment(
      env,
      [&](const StartExecutionCallbackInfo& info) -> MaybeLocal<Value> {
        // This is a slightly hacky way to convert UTF-8 to UTF-16.
        Local<String> str =
            String::NewFromUtf8(env->isolate(),
                                main_script_source_utf8).ToLocalChecked();
        auto main_utf16 = std::make_unique<String::Value>(env->isolate(), str);

        // TODO(addaleax): Avoid having a global table for all scripts.
        std::string name = "embedder_main_" + std::to_string(env->thread_id());
        native_module::NativeModuleEnv::Add(
            name.c_str(),
            UnionBytes(**main_utf16, main_utf16->length()));
        env->set_main_utf16(std::move(main_utf16));
        std::vector<Local<String>> params = {
            env->process_string(),
            env->require_string()};
        std::vector<Local<Value>> args = {
            env->process_object(),
            env->native_module_require()};
        return ExecuteBootstrapper(env, name.c_str(), &params, &args);
      });
}

Environment* GetCurrentEnvironment(Local<Context> context) {
  return Environment::GetCurrent(context);
}

MultiIsolatePlatform* GetMainThreadMultiIsolatePlatform() {
  return per_process::v8_platform.Platform();
}

MultiIsolatePlatform* GetMultiIsolatePlatform(Environment* env) {
  return GetMultiIsolatePlatform(env->isolate_data());
}

MultiIsolatePlatform* GetMultiIsolatePlatform(IsolateData* env) {
  return env->platform();
}

MultiIsolatePlatform* CreatePlatform(
    int thread_pool_size,
    node::tracing::TracingController* tracing_controller) {
  return CreatePlatform(
      thread_pool_size,
      static_cast<v8::TracingController*>(tracing_controller));
}

MultiIsolatePlatform* CreatePlatform(
    int thread_pool_size,
    v8::TracingController* tracing_controller) {
  return MultiIsolatePlatform::Create(thread_pool_size, tracing_controller)
      .release();
}

void FreePlatform(MultiIsolatePlatform* platform) {
  delete platform;
}

std::unique_ptr<MultiIsolatePlatform> MultiIsolatePlatform::Create(
    int thread_pool_size,
    v8::TracingController* tracing_controller) {
  return std::make_unique<NodePlatform>(thread_pool_size, tracing_controller);
}

MaybeLocal<Object> GetPerContextExports(Local<Context> context) {
  Isolate* isolate = context->GetIsolate();
  EscapableHandleScope handle_scope(isolate);

  Local<Object> global = context->Global();
  Local<Private> key = Private::ForApi(isolate,
      FIXED_ONE_BYTE_STRING(isolate, "node:per_context_binding_exports"));

  Local<Value> existing_value;
  if (!global->GetPrivate(context, key).ToLocal(&existing_value))
    return MaybeLocal<Object>();
  if (existing_value->IsObject())
    return handle_scope.Escape(existing_value.As<Object>());

  Local<Object> exports = Object::New(isolate);
  if (context->Global()->SetPrivate(context, key, exports).IsNothing() ||
      !InitializePrimordials(context))
    return MaybeLocal<Object>();
  return handle_scope.Escape(exports);
}

// Any initialization logic should be performed in
// InitializeContext, because embedders don't necessarily
// call NewContext and so they will experience breakages.
Local<Context> NewContext(Isolate* isolate,
                          Local<ObjectTemplate> object_template) {
  auto context = Context::New(isolate, nullptr, object_template);
  if (context.IsEmpty()) return context;

  if (!InitializeContext(context)) {
    return Local<Context>();
  }

  return context;
}

void ProtoThrower(const FunctionCallbackInfo<Value>& info) {
  THROW_ERR_PROTO_ACCESS(info.GetIsolate());
}

// This runs at runtime, regardless of whether the context
// is created from a snapshot.
void InitializeContextRuntime(Local<Context> context) {
  Isolate* isolate = context->GetIsolate();
  HandleScope handle_scope(isolate);

  // Delete `Intl.v8BreakIterator`
  // https://github.com/nodejs/node/issues/14909
  Local<String> intl_string = FIXED_ONE_BYTE_STRING(isolate, "Intl");
  Local<String> break_iter_string =
    FIXED_ONE_BYTE_STRING(isolate, "v8BreakIterator");
  Local<Value> intl_v;
  if (context->Global()->Get(context, intl_string).ToLocal(&intl_v) &&
      intl_v->IsObject()) {
    Local<Object> intl = intl_v.As<Object>();
    intl->Delete(context, break_iter_string).Check();
  }

  // Delete `Atomics.wake`
  // https://github.com/nodejs/node/issues/21219
  Local<String> atomics_string = FIXED_ONE_BYTE_STRING(isolate, "Atomics");
  Local<String> wake_string = FIXED_ONE_BYTE_STRING(isolate, "wake");
  Local<Value> atomics_v;
  if (context->Global()->Get(context, atomics_string).ToLocal(&atomics_v) &&
      atomics_v->IsObject()) {
    Local<Object> atomics = atomics_v.As<Object>();
    atomics->Delete(context, wake_string).Check();
  }

  // Remove __proto__
  // https://github.com/nodejs/node/issues/31951
  Local<String> object_string = FIXED_ONE_BYTE_STRING(isolate, "Object");
  Local<String> prototype_string = FIXED_ONE_BYTE_STRING(isolate, "prototype");
  Local<Object> prototype = context->Global()
                                ->Get(context, object_string)
                                .ToLocalChecked()
                                .As<Object>()
                                ->Get(context, prototype_string)
                                .ToLocalChecked()
                                .As<Object>();
  Local<String> proto_string = FIXED_ONE_BYTE_STRING(isolate, "__proto__");
  if (per_process::cli_options->disable_proto == "delete") {
    prototype->Delete(context, proto_string).ToChecked();
  } else if (per_process::cli_options->disable_proto == "throw") {
    Local<Value> thrower =
        Function::New(context, ProtoThrower).ToLocalChecked();
    PropertyDescriptor descriptor(thrower, thrower);
    descriptor.set_enumerable(false);
    descriptor.set_configurable(true);
    prototype->DefineProperty(context, proto_string, descriptor).ToChecked();
  } else if (per_process::cli_options->disable_proto != "") {
    // Validated in ProcessGlobalArgs
    FatalError("InitializeContextRuntime()", "invalid --disable-proto mode");
  }
}

bool InitializeContextForSnapshot(Local<Context> context) {
  Isolate* isolate = context->GetIsolate();
  HandleScope handle_scope(isolate);

  context->SetEmbedderData(ContextEmbedderIndex::kAllowWasmCodeGeneration,
                           True(isolate));
  return InitializePrimordials(context);
}

bool InitializePrimordials(Local<Context> context) {
  // Run per-context JS files.
  Isolate* isolate = context->GetIsolate();
  Context::Scope context_scope(context);
  Local<Object> exports;

  Local<String> primordials_string =
      FIXED_ONE_BYTE_STRING(isolate, "primordials");
  Local<String> global_string = FIXED_ONE_BYTE_STRING(isolate, "global");
  Local<String> exports_string = FIXED_ONE_BYTE_STRING(isolate, "exports");

  // Create primordials first and make it available to per-context scripts.
  Local<Object> primordials = Object::New(isolate);
  if (!primordials->SetPrototype(context, Null(isolate)).FromJust() ||
      !GetPerContextExports(context).ToLocal(&exports) ||
      !exports->Set(context, primordials_string, primordials).FromJust()) {
    return false;
  }

  static const char* context_files[] = {"internal/per_context/primordials",
                                        "internal/per_context/domexception",
                                        "internal/per_context/messageport",
                                        nullptr};

  for (const char** module = context_files; *module != nullptr; module++) {
    std::vector<Local<String>> parameters = {
        global_string, exports_string, primordials_string};
    Local<Value> arguments[] = {context->Global(), exports, primordials};
    MaybeLocal<Function> maybe_fn =
        native_module::NativeModuleEnv::LookupAndCompile(
            context, *module, &parameters, nullptr);
    Local<Function> fn;
    if (!maybe_fn.ToLocal(&fn)) {
      return false;
    }
    MaybeLocal<Value> result =
        fn->Call(context, Undefined(isolate), arraysize(arguments), arguments);
    // Execution failed during context creation.
    // TODO(joyeecheung): deprecate this signature and return a MaybeLocal.
    if (result.IsEmpty()) {
      return false;
    }
  }

  return true;
}

bool InitializeContext(Local<Context> context) {
  if (!InitializeContextForSnapshot(context)) {
    return false;
  }

  InitializeContextRuntime(context);
  return true;
}

uv_loop_t* GetCurrentEventLoop(Isolate* isolate) {
  HandleScope handle_scope(isolate);
  Local<Context> context = isolate->GetCurrentContext();
  if (context.IsEmpty()) return nullptr;
  Environment* env = Environment::GetCurrent(context);
  if (env == nullptr) return nullptr;
  return env->event_loop();
}

void AddLinkedBinding(Environment* env, const node_module& mod) {
  CHECK_NOT_NULL(env);
  Mutex::ScopedLock lock(env->extra_linked_bindings_mutex());

  node_module* prev_head = env->extra_linked_bindings_head();
  env->extra_linked_bindings()->push_back(mod);
  if (prev_head != nullptr)
    prev_head->nm_link = &env->extra_linked_bindings()->back();
}

void AddLinkedBinding(Environment* env,
                      const char* name,
                      addon_context_register_func fn,
                      void* priv) {
  node_module mod = {
    NODE_MODULE_VERSION,
    NM_F_LINKED,
    nullptr,  // nm_dso_handle
    nullptr,  // nm_filename
    nullptr,  // nm_register_func
    fn,
    name,
    priv,
    nullptr   // nm_link
  };
  AddLinkedBinding(env, mod);
}

static std::atomic<uint64_t> next_thread_id{0};

ThreadId AllocateEnvironmentThreadId() {
  return ThreadId { next_thread_id++ };
}

void DefaultProcessExitHandler(Environment* env, int exit_code) {
  env->set_can_call_into_js(false);
  env->stop_sub_worker_contexts();
  DisposePlatform();
  exit(exit_code);
}


void SetProcessExitHandler(Environment* env,
                           std::function<void(Environment*, int)>&& handler) {
  env->set_process_exit_handler(std::move(handler));
}

}  // namespace node