From a907870aafe8273da3a70e281bc540b6d5ff0085 Mon Sep 17 00:00:00 2001 From: Chengzhong Wu Date: Tue, 16 May 2023 19:58:41 +0800 Subject: [PATCH] fixup! src: add Realm document in the src README.md --- src/README.md | 41 ++++++++++++++++++++++++++--------------- 1 file changed, 26 insertions(+), 15 deletions(-) diff --git a/src/README.md b/src/README.md index e4f3e108e78fce..b87132c014cb99 100644 --- a/src/README.md +++ b/src/README.md @@ -265,12 +265,16 @@ heap. Node.js exposes this ability through the [`vm` module][]. V8 refers to each of these global objects and their associated builtins as a `Context`. -Currently, in Node.js there is one main `Context` associated with a -[`Realm`][] instance, and most Node.js features will only work inside -that context. (The only exception at the time of writing are -[`MessagePort`][] objects.) This restriction is not inherent to the design of -Node.js, and a sufficiently committed person could restructure Node.js to -provide built-in modules inside of `vm.Context`s. +Currently, in Node.js there is one main `Context` associated with the +principal [`Realm`][] of an [`Environment`][] instance, and a number of +subsidiary `Context`s that are created with `vm.Context` or associated with +[`ShadowRealm`][]. + +Most Node.js features will only work inside a context associated with a +`Realm`. The only exception at the time of writing are [`MessagePort`][] +objects. This restriction is not inherent to the design of Node.js, and a +sufficiently committed person could restructure Node.js to provide built-in +modules inside of `vm.Context`s. Often, the `Context` is passed around for [exception handling][]. Typical ways of accessing the current `Context` in the Node.js code are: @@ -310,7 +314,7 @@ Currently, every `Environment` class is associated with: The `Environment` class contains a large number of different fields for different built-in modules that can be shared across different `Realm` -instances, for example a libuv timer for `setTimeout()`. +instances, for example, the inspector agent, async hooks info. Typical ways of accessing the current `Environment` in the Node.js code are: @@ -329,20 +333,25 @@ Typical ways of accessing the current `Environment` in the Node.js code are: ### `Realm` The `Realm` class is a container for a set of JavaScript objects and functions -that are associated with a particular ECMAScript global environment. +that are associated with a particular [ECMAScript realm][]. -Every `Realm` instance is associated with a [`Context`][]. +Each ECMAScript realm comes with a global object and a set of intrinsic +objects. An ECMAScript realm has a `[[HostDefined]]` field, which represents +the Node.js [`Realm`][] object. -A `Realm` can be a principal realm or a synthetic realm. A principal realm is -created with an `Environment` as its principal global environment to evaluate -scripts. A synthetic realm is created with JS APIs like `ShadowRealm`. +Every `Realm` instance is created for a particular [`Context`][]. A `Realm` +can be a principal realm or a synthetic realm. A principal realm is created +for each `Environment`'s main [`Context`][]. A synthetic realm is created +for the [`Context`][] of each [`ShadowRealm`][] constructed from the JS API. No +`Realm` is created for the [`Context`][] of a `vm.Context`. Native bindings and built-in modules can be evaluated in either a principal realm or a synthetic realm. The `Realm` class contains a large number of different fields for -different built-in modules, for example the memory for a `Float64Array` that -the `fs` module uses for storing data returned from a `fs.stat()` call. +different built-in modules, for example the memory for a `Uint32Array` that +the `url` module uses for storing data returned from a +`urlBinding.update()` call. It also provides [cleanup hooks][] and maintains a list of [`BaseObject`][] instances. @@ -356,7 +365,7 @@ Typical ways of accessing the current `Realm` in the Node.js code are: This requires that `context` has been associated with the `Realm` instance, e.g. is the principal `Realm` for the `Environment`. * Given an [`Isolate`][], using `Realm::GetCurrent(isolate)`. This looks - up the current [`Context`][] and then uses that. + up the current [`Context`][] and then uses its `Realm`. @@ -1073,6 +1082,7 @@ static void GetUserInfo(const FunctionCallbackInfo& args) { [C++ coding style]: ../doc/contributing/cpp-style-guide.md [Callback scopes]: #callback-scopes +[ECMAScript realm]: https://tc39.es/ecma262/#sec-code-realms [JavaScript value handles]: #js-handles [N-API]: https://nodejs.org/api/n-api.html [`BaseObject`]: #baseobject @@ -1087,6 +1097,7 @@ static void GetUserInfo(const FunctionCallbackInfo& args) { [`MessagePort`]: https://nodejs.org/api/worker_threads.html#worker_threads_class_messageport [`Realm`]: #realm [`ReqWrap`]: #reqwrap +[`ShadowRealm`]: https://github.com/tc39/proposal-shadowrealm [`async_hooks` module]: https://nodejs.org/api/async_hooks.html [`async_wrap.h`]: async_wrap.h [`base_object.h`]: base_object.h