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doc: avoid using v8::Persistent in addon docs · nodejs/node@5340361 · GitHub

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Commit 5340361

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addaleax
authored and
BethGriggs
committed
doc: avoid using v8::Persistent in addon docs
Use `v8::Global` where possible. For examples where it applies, also clean up the code and make the code multi-threading-ready, for those where that isn’t easily possible, add a warning about that. PR-URL: #31018 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Richard Lau <riclau@uk.ibm.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Gus Caplan <me@gus.host> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
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‎doc/api/addons.md‎

Lines changed: 37 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -157,11 +157,11 @@ The context-aware addon can be structured to avoid global static data by
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performing the following steps:
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* defining a class which will hold per-addon-instance data. Such
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a class should include a `v8::Persistent<v8::Object>` which will hold a weak
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a class should include a `v8::Global<v8::Object>` which will hold a weak
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reference to the addon's `exports` object. The callback associated with the weak
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reference will then destroy the instance of the class.
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* constructing an instance of this class in the addon initializer such that the
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`v8::Persistent<v8::Object>` is set to the `exports` object.
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`v8::Global<v8::Object>` is set to the `exports` object.
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* storing the instance of the class in a `v8::External`, and
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* passing the `v8::External` to all methods exposed to JavaScript by passing it
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to the `v8::FunctionTemplate` constructor which creates the native-backed
@@ -188,14 +188,6 @@ class AddonData {
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exports_.SetWeak(this, DeleteMe, WeakCallbackType::kParameter);
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}
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~AddonData() {
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if (!exports_.IsEmpty()) {
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// Reset the reference to avoid leaking data.
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exports_.ClearWeak();
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exports_.Reset();
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}
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}
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// Per-addon data.
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int call_count;
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@@ -207,7 +199,7 @@ class AddonData {
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// Weak handle to the "exports" object. An instance of this class will be
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// destroyed along with the exports object to which it is weakly bound.
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v8::Persistent<v8::Object> exports_;
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v8::Global<v8::Object> exports_;
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};
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static void Method(const v8::FunctionCallbackInfo<v8::Value>& info) {
@@ -830,7 +822,7 @@ class MyObject : public node::ObjectWrap {
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static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
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static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
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static v8::Persistent<v8::Function> constructor;
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double value_;
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};
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@@ -858,12 +850,10 @@ using v8::Local;
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using v8::NewStringType;
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using v8::Number;
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using v8::Object;
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using v8::Persistent;
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using v8::ObjectTemplate;
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using v8::String;
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using v8::Value;
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Persistent<Function> MyObject::constructor;
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MyObject::MyObject(double value) : value_(value) {
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}
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@@ -872,21 +862,27 @@ MyObject::~MyObject() {
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void MyObject::Init(Local<Object> exports) {
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Isolate* isolate = exports->GetIsolate();
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Local<Context> context = isolate->GetCurrentContext();
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Local<ObjectTemplate> addon_data_tpl = ObjectTemplate::New(isolate);
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addon_data_tpl->SetInternalFieldCount(1); // 1 field for the MyObject::New()
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Local<Object> addon_data =
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addon_data_tpl->NewInstance(context).ToLocalChecked();
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// Prepare constructor template
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Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
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Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New, addon_data);
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tpl->SetClassName(String::NewFromUtf8(
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isolate, "MyObject", NewStringType::kNormal).ToLocalChecked());
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tpl->InstanceTemplate()->SetInternalFieldCount(1);
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// Prototype
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NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
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Local<Context> context = isolate->GetCurrentContext();
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constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked());
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Local<Function> constructor = tpl->GetFunction(context).ToLocalChecked();
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addon_data->SetInternalField(0, constructor);
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exports->Set(context, String::NewFromUtf8(
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isolate, "MyObject", NewStringType::kNormal).ToLocalChecked(),
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tpl->GetFunction(context).ToLocalChecked()).FromJust();
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constructor).FromJust();
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}
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void MyObject::New(const FunctionCallbackInfo<Value>& args) {
@@ -904,7 +900,8 @@ void MyObject::New(const FunctionCallbackInfo<Value>& args) {
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// Invoked as plain function `MyObject(...)`, turn into construct call.
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const int argc = 1;
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Local<Value> argv[argc] = { args[0] };
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Local<Function> cons = Local<Function>::New(isolate, constructor);
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Local<Function> cons =
904+
args.Data().As<Object>()->GetInternalField(0).As<Function>();
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Local<Object> result =
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cons->NewInstance(context, argc, argv).ToLocalChecked();
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args.GetReturnValue().Set(result);
@@ -1029,7 +1026,7 @@ class MyObject : public node::ObjectWrap {
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10301027
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
10311028
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
1032-
static v8::Persistent<v8::Function> constructor;
1029+
static v8::Global<v8::Function> constructor;
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double value_;
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};
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@@ -1047,20 +1044,23 @@ The implementation in `myobject.cc` is similar to the previous example:
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10481045
namespace demo {
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1047+
using node::AddEnvironmentCleanupHook;
10501048
using v8::Context;
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using v8::Function;
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using v8::FunctionCallbackInfo;
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using v8::FunctionTemplate;
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using v8::Global;
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using v8::Isolate;
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using v8::Local;
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using v8::NewStringType;
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using v8::Number;
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using v8::Object;
1059-
using v8::Persistent;
10601058
using v8::String;
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using v8::Value;
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1063-
Persistent<Function> MyObject::constructor;
1061+
// Warning! This is not thread-safe, this addon cannot be used for worker
1062+
// threads.
1063+
Global<Function> MyObject::constructor;
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10651065
MyObject::MyObject(double value) : value_(value) {
10661066
}
@@ -1080,6 +1080,10 @@ void MyObject::Init(Isolate* isolate) {
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10811081
Local<Context> context = isolate->GetCurrentContext();
10821082
constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked());
1083+
1084+
AddEnvironmentCleanupHook(isolate, [](void*) {
1085+
constructor.Reset();
1086+
}, nullptr);
10831087
}
10841088

10851089
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
@@ -1246,7 +1250,7 @@ class MyObject : public node::ObjectWrap {
12461250
~MyObject();
12471251
12481252
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
1249-
static v8::Persistent<v8::Function> constructor;
1253+
static v8::Global<v8::Function> constructor;
12501254
double value_;
12511255
};
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@@ -1264,19 +1268,22 @@ The implementation of `myobject.cc` is similar to before:
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12651269
namespace demo {
12661270

1271+
using node::AddEnvironmentCleanupHook;
12671272
using v8::Context;
12681273
using v8::Function;
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using v8::FunctionCallbackInfo;
12701275
using v8::FunctionTemplate;
1276+
using v8::Global;
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using v8::Isolate;
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using v8::Local;
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using v8::NewStringType;
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using v8::Object;
1275-
using v8::Persistent;
12761281
using v8::String;
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using v8::Value;
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1279-
Persistent<Function> MyObject::constructor;
1284+
// Warning! This is not thread-safe, this addon cannot be used for worker
1285+
// threads.
1286+
Global<Function> MyObject::constructor;
12801287

12811288
MyObject::MyObject(double value) : value_(value) {
12821289
}
@@ -1293,6 +1300,10 @@ void MyObject::Init(Isolate* isolate) {
12931300

12941301
Local<Context> context = isolate->GetCurrentContext();
12951302
constructor.Reset(isolate, tpl->GetFunction(context).ToLocalChecked());
1303+
1304+
AddEnvironmentCleanupHook(isolate, [](void*) {
1305+
constructor.Reset();
1306+
}, nullptr);
12961307
}
12971308

12981309
void MyObject::New(const FunctionCallbackInfo<Value>& args) {

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