feature(neon): API for thread-local data

crates/neon/Cargo.toml

@@ -23,6 +23,7 @@ nodejs-sys = "0.13.0"
 libloading = "0.7.3"
 semver = "0.9.0"
 smallvec = "1.4.2"
+once_cell = "1.10.0"
 neon-macros = { version = "=0.10.1", path = "../neon-macros" }
 
 [features]

crates/neon/src/instance/mod.rs

@@ -0,0 +1,72 @@
+use std::any::Any;
+use std::marker::PhantomData;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use once_cell::sync::OnceCell;
+
+use crate::context::Context;
+use crate::lifecycle::InstanceData;
+
+static COUNTER: AtomicUsize = AtomicUsize::new(0);
+
+fn next_id() -> usize {
+    COUNTER.fetch_add(1, Ordering::SeqCst)
+}
+
+/// A cell that can be used to allocate data that is global to an instance
+/// of a Neon addon.
+pub struct Global<T> {
+    _type: PhantomData<T>,
+    id: OnceCell<usize>,
+}
+
+impl<T> Global<T> {
+    pub const fn new() -> Self {
+        Self {
+            _type: PhantomData,
+            id: OnceCell::new(),
+        }
+    }
+
+    fn id(&self) -> usize {
+        *self.id.get_or_init(next_id)
+    }
+}
+
+impl<T: Any + Send> Global<T> {
+    pub fn borrow<'a, 'b, C>(&self, cx: &'b mut C) -> Option<&'b T>
+    where
+        C: Context<'a>,
+    {
+        InstanceData::globals(cx)[self.id()]
+            .as_ref()
+            .map(|boxed| boxed.downcast_ref().unwrap())
+    }
+
+    pub fn borrow_mut<'a, 'b, C>(&self, cx: &'b mut C) -> Option<&'b mut T>
+    where
+        C: Context<'a>,
+    {
+        InstanceData::globals(cx)[self.id()]
+            .as_mut()
+            .map(|boxed| boxed.downcast_mut().unwrap())
+    }
+
+    pub fn set<'a, 'b, C>(&self, cx: &'b mut C, v: T)
+    where
+        C: Context<'a>,
+    {
+        InstanceData::globals(cx)[self.id()] = Some(Box::new(v));
+    }
+}
+
+impl<T: Any + Send + Clone> Global<T> {
+    pub fn get<'a, C>(&self, cx: &mut C) -> Option<T>
+    where
+        C: Context<'a>,
+    {
+        InstanceData::globals(cx)[self.id()]
+            .as_ref()
+            .map(|boxed| boxed.downcast_ref::<T>().unwrap().clone())
+    }
+}

crates/neon/src/lib.rs

@@ -81,6 +81,8 @@
 pub mod context;
 pub mod event;
 pub mod handle;
+#[cfg(feature = "napi-6")]
+pub mod instance;
 pub mod meta;
 pub mod object;
 pub mod prelude;

crates/neon/src/lifecycle.rs

@@ -8,9 +8,13 @@
 //!
 //! [napi-docs]: https://nodejs.org/api/n-api.html#n_api_environment_life_cycle_apis
 
-use std::sync::{
-    atomic::{AtomicU64, Ordering},
-    Arc,
+use std::{
+    any::Any,
+    ops::{Index, IndexMut},
+    sync::{
+        atomic::{AtomicU64, Ordering},
+        Arc,
+    },
 };
 
 use crate::{
@@ -54,6 +58,36 @@ pub(crate) struct InstanceData {
 
     /// Shared `Channel` that is cloned to be returned by the `cx.channel()` method
     shared_channel: Channel,
+
+    /// Table of user-defined global cells.
+    globals: GlobalTable,
+}
+
+pub(crate) struct GlobalTable {
+    cells: Vec<Option<Box<dyn Any + Send>>>,
+}
+
+impl GlobalTable {
+    fn new() -> Self {
+        Self { cells: Vec::new() }
+    }
+}
+
+impl Index<usize> for GlobalTable {
+    type Output = Option<Box<dyn Any + Send>>;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.cells[index]
+    }
+}
+
+impl IndexMut<usize> for GlobalTable {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        if index >= self.cells.len() {
+            self.cells.resize_with(index + 1, Default::default);
+        }
+        &mut self.cells[index]
+    }
 }
 
 /// Wrapper for raw Node-API values to be dropped on the main thread
@@ -83,7 +117,7 @@ impl InstanceData {
     /// # Safety
     /// No additional locking (e.g., `Mutex`) is necessary because holding a
     /// `Context` reference ensures serialized access.
-    pub(crate) fn get<'a, C: Context<'a>>(cx: &mut C) -> &'a mut InstanceData {
+    pub(crate) fn get<'a, C: Context<'a>>(cx: &mut C) -> &mut InstanceData {
         let env = cx.env().to_raw();
         let data = unsafe { lifecycle::get_instance_data::<InstanceData>(env).as_mut() };
 
@@ -107,6 +141,7 @@ impl InstanceData {
             id: InstanceId::next(),
             drop_queue: Arc::new(drop_queue),
             shared_channel,
+            globals: GlobalTable::new(),
         };
 
         unsafe { &mut *lifecycle::set_instance_data(env, data) }
@@ -129,4 +164,9 @@ impl InstanceData {
     pub(crate) fn id<'a, C: Context<'a>>(cx: &mut C) -> InstanceId {
         InstanceData::get(cx).id
     }
+
+    /// Helper to return a reference to the `globals` field of `InstanceData`.
+    pub(crate) fn globals<'a, C: Context<'a>>(cx: &mut C) -> &mut GlobalTable {
+        &mut InstanceData::get(cx).globals
+    }
 }

test/napi/lib/workers.js

@@ -1,10 +1,11 @@
 const assert = require("assert");
-const { Worker, isMainThread, parentPort } = require("worker_threads");
+const { Worker, isMainThread, parentPort, threadId } = require("worker_threads");
 
 const addon = require("..");
 
 // Receive a message, try that method and return the error message
 if (!isMainThread) {
+  addon.set_thread_id(threadId);
   parentPort.once("message", (message) => {
     try {
       switch (message) {
@@ -17,6 +18,12 @@ if (!isMainThread) {
         case "get_or_init_clone":
           addon.get_or_init_clone(() => ({}));
           break;
+        case "get_thread_id":
+          {
+            let id = addon.get_thread_id();
+            parentPort.postMessage(id);
+          }
+          break;
         default:
           throw new Error(`Unexpected message: ${message}`);
       }
@@ -30,6 +37,11 @@ if (!isMainThread) {
   return;
 }
 
+// From here on, we're in the main thread.
+
+// Set the `THREAD_ID` Global value in the main thread cell.
+addon.set_thread_id(threadId);
+
 describe("Worker / Root Tagging Tests", () => {
   describe("Single Threaded", () => {
     it("should be able to stash a global with `get_and_replace`", () => {
@@ -106,3 +118,26 @@ describe("Worker / Root Tagging Tests", () => {
     });
   });
 });
+
+describe("Globals", () => {
+  it("should be able to read an instance global from the main thread", () => {
+    let lookedUpId = addon.get_thread_id();
+    assert.strictEqual(lookedUpId, threadId);
+  });
+
+  it("should allocate separate globals for each addon instance", (cb) => {
+    let mainThreadId = addon.get_thread_id();
+
+    const worker = new Worker(__filename);
+
+    worker.once("message", (message) => {
+      assert.strictEqual(typeof message, 'number');
+      assert.notStrictEqual(message, mainThreadId);
+      let mainThreadIdAgain = addon.get_thread_id();
+      assert.strictEqual(mainThreadIdAgain, mainThreadId);
+      cb();
+    });
+
+    worker.postMessage("get_thread_id");
+  });
+});

test/napi/src/js/workers.rs

@@ -2,6 +2,7 @@ use std::sync::Mutex;
 
 use once_cell::sync::{Lazy, OnceCell};
 
+use neon::instance::Global;
 use neon::prelude::*;
 
 pub fn get_and_replace(mut cx: FunctionContext) -> JsResult<JsValue> {
@@ -44,3 +45,19 @@ pub fn get_or_init_clone(mut cx: FunctionContext) -> JsResult<JsObject> {
     // test the `clone` method.
     Ok(o.clone(&mut cx).into_inner(&mut cx))
 }
+
+static THREAD_ID: Global<u32> = Global::new();
+
+pub fn set_thread_id(mut cx: FunctionContext) -> JsResult<JsUndefined> {
+    let id = cx.argument::<JsNumber>(0)?.value(&mut cx) as u32;
+    THREAD_ID.set(&mut cx, id);
+    Ok(cx.undefined())
+}
+
+pub fn get_thread_id(mut cx: FunctionContext) -> JsResult<JsValue> {
+    let id = THREAD_ID.get(&mut cx);
+    Ok(match id {
+        Some(id) => cx.number(id).upcast(),
+        None => cx.undefined().upcast(),
+    })
+}

test/napi/src/lib.rs

@@ -340,6 +340,8 @@ fn main(mut cx: ModuleContext) -> NeonResult<()> {
     cx.export_function("get_and_replace", js::workers::get_and_replace)?;
     cx.export_function("get_or_init", js::workers::get_or_init)?;
     cx.export_function("get_or_init_clone", js::workers::get_or_init_clone)?;
+    cx.export_function("get_thread_id", js::workers::get_thread_id)?;
+    cx.export_function("set_thread_id", js::workers::set_thread_id)?;
 
     Ok(())
 }