squash! worker: improve integration with native addons

doc/api/addons.md

@@ -232,6 +232,23 @@ NODE_MODULE_INIT(/* exports, module, context */) {
 }
 ```
 
+#### Worker support
+
+In order to support [`Worker`][] threads, addons need to clean up any resources
+they may have allocated when such a thread exists. This can be achieved through
+the usage of the `AddEnvironmentCleanupHook()` function:
+
+```c++
+void AddEnvironmentCleanupHook(v8::Isolate* isolate,
+                               void (*fun)(void* arg),
+                               void* arg);
+```
+
+This function adds a hook that will run before a given Node.js instance shuts
+down. If necessary, such hooks can be removed using
+`RemoveEnvironmentCleanupHook()` before they are run, which has the same
+signature.
+
 ### Building
 
 Once the source code has been written, it must be compiled into the binary
@@ -1316,6 +1333,7 @@ Test in JavaScript by running:
 require('./build/Release/addon');
 ```
 
+[`Worker`]: worker_threads.html#worker_threads_class_worker
 [Electron]: https://electronjs.org/
 [Embedder's Guide]: https://github.com/v8/v8/wiki/Embedder's%20Guide
 [Linking to Node.js' own dependencies]: #addons_linking_to_node_js_own_dependencies

doc/api/worker_threads.md

@@ -253,11 +253,9 @@ Notable differences inside a Worker environment are:
 - Execution may stop at any point as a result of [`worker.terminate()`][]
   being invoked.
 - IPC channels from parent processes are not accessible.
-
-Currently, the following differences also exist until they are addressed:
-
-- The [`inspector`][] module is not available yet.
-- Native addons are not supported yet.
+- Native add-ons are unloaded if they are only used inside `Worker` instances
+  when those workers shut down.
+  See the [addons documentation][] for more detials.
 
 Creating `Worker` instances inside of other `Worker`s is possible.
 
@@ -484,7 +482,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`require('worker_threads').parentPort`]: #worker_threads_worker_parentport
 [`require('worker_threads').threadId`]: #worker_threads_worker_threadid
 [`cluster` module]: cluster.html
-[`inspector`]: inspector.html
+[addons documentation]: addons.html#addons_worker_support
 [v8.serdes]: v8.html#v8_serialization_api
 [`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
 [Signals events]: process.html#process_signal_events