doc: update FreeEnvironment() notes for sibling Environments

With the FreeEnvironment() fix for sibling Environments and the handle
cleanup depth tracked per thread, only the Environment being freed
loses JavaScript while FreeEnvironment() runs the shared loop. Callbacks
of the other Environments on that loop run their JavaScript as usual.
Update embedding.md and the comment in node.h, which still describe
JavaScript as disallowed on the whole isolate.

Signed-off-by: Shelley Vohr <shelley.vohr@gmail.com>

Author: codebytere

doc/api/embedding.md

@@ -95,13 +95,10 @@ to as `node::Environment`. Each `node::Environment` is associated with:
 
 `node::Environment`s that share a `node::IsolateData` also share its
 `uv_loop_t`. `node::FreeEnvironment()` runs that loop until the handles of the
-`node::Environment` being freed have closed, and JavaScript execution is
-disallowed on the whole `v8::Isolate` while it does, so pending timers, I/O
-callbacks and thread pool completions that belong to other `node::Environment`s
-on the same loop can run inside that call without being able to call into
-JavaScript. `node::Environment`s that are freed independently of one another
-should each use their own `uv_loop_t` and `node::IsolateData`, or the embedder
-should make sure the others have no pending work when one of them is freed.
+`node::Environment` being freed have closed. Timers, I/O callbacks and thread
+pool completions of the other `node::Environment`s that become due in those
+loop iterations run normally, including their JavaScript; only the
+`node::Environment` being freed can no longer call into JavaScript.
 
 In order to set up a `v8::Isolate`, an `v8::ArrayBuffer::Allocator` needs
 to be provided. One possible choice is the default Node.js allocator, which

src/node.h

@@ -889,8 +889,8 @@ NODE_EXTERN v8::MaybeLocal<v8::Value> LoadEnvironment(
     EmbedderPreloadCallback preload = nullptr);
 
 // Runs `env`'s event loop until its handles have closed, with JavaScript
-// execution disallowed on the isolate; see doc/api/embedding.md if that loop
-// is shared with other Environments.
+// execution disallowed for `env`; see doc/api/embedding.md if that loop is
+// shared with other Environments.
 NODE_EXTERN void FreeEnvironment(Environment* env);
 
 // Set a callback that is called when process.exit() is called from JS,