Call sync functions within tokio runtime

crates/backend/src/codegen/fn.rs

@@ -21,10 +21,12 @@ impl TryToTokens for NapiFn {
 
     let native_call = if !self.is_async {
       quote! {
-        let #receiver_ret_name = {
-          #receiver(#(#arg_names),*)
-        };
-        #ret
+        napi::bindgen_prelude::within_runtime_if_available(move || {
+          let #receiver_ret_name = {
+            #receiver(#(#arg_names),*)
+          };
+          #ret
+        })
       }
     } else {
       let call = if self.is_ret_result {

crates/napi/src/lib.rs

@@ -162,6 +162,16 @@ pub mod bindgen_prelude {
     assert_type_of, bindgen_runtime::*, check_status, check_status_or_throw, error, error::*, sys,
     type_of, JsError, Property, PropertyAttributes, Result, Status, Task, ValueType,
   };
+
+  // This function's signature must be kept in sync with the one in tokio_runtime.rs, otherwise napi
+  // will fail to compile without the `tokio_rt` feature.
+
+  /// If the feature `tokio_rt` has been enabled this will enter the runtime context and
+  /// then call the provided closure. Otherwise it will just call the provided closure.
+  #[cfg(not(all(feature = "tokio_rt", feature = "napi4")))]
+  pub fn within_runtime_if_available<F: FnOnce() -> T, T>(f: F) -> T {
+    f()
+  }
 }
 
 #[doc(hidden)]

crates/napi/src/tokio_runtime.rs

@@ -59,6 +59,16 @@ where
   RT.0.spawn(fut);
 }
 
+// This function's signature must be kept in sync with the one in lib.rs, otherwise napi
+// will fail to compile with the `tokio_rt` feature.
+
+/// If the feature `tokio_rt` has been enabled this will enter the runtime context and
+/// then call the provided closure. Otherwise it will just call the provided closure.
+pub fn within_runtime_if_available<F: FnOnce() -> T, T>(f: F) -> T {
+  let _rt_guard = RT.0.enter();
+  f()
+}
+
 #[allow(clippy::not_unsafe_ptr_arg_deref)]
 pub fn execute_tokio_future<
   Data: 'static + Send,

examples/napi/Cargo.toml

@@ -25,6 +25,7 @@ napi-derive = { path = "../../crates/macro", features = ["type-def"] }
 serde = "1"
 serde_derive = "1"
 serde_json = "1"
+tokio = { version = "1.20.0", features = ["full"] }
 
 [build-dependencies]
 napi-build = { path = "../../crates/build" }

examples/napi/__test__/typegen.spec.ts.md

@@ -179,6 +179,7 @@ Generated by [AVA](https://avajs.dev).
     export function threadsafeFunctionThrowError(cb: (...args: any[]) => any): void␊
     export function threadsafeFunctionFatalMode(cb: (...args: any[]) => any): void␊
     export function threadsafeFunctionFatalModeError(cb: (...args: any[]) => any): void␊
+    export function useTokioWithoutAsync(): void␊
     export function getBuffer(): Buffer␊
     export function appendBuffer(buf: Buffer): Buffer␊
     export function getEmptyBuffer(): Buffer␊

examples/napi/__test__/values.spec.ts

@@ -103,6 +103,7 @@ import {
   receiveObjectWithClassField,
   AnotherClassForEither,
   receiveDifferentClass,
+  useTokioWithoutAsync,
 } from '../'
 
 test('export const', (t) => {
@@ -691,6 +692,12 @@ Napi4Test('await Promise in rust', async (t) => {
   t.is(result, fx + 100)
 })
 
+Napi4Test('Run function which uses tokio internally but is not async', (t) => {
+  useTokioWithoutAsync()
+  // The prior didn't throw an exception, so it worked.
+  t.assert(true)
+})
+
 Napi4Test('Promise should reject raw error in rust', async (t) => {
   const fxError = new Error('What is Happy Planet')
   const err = await t.throwsAsync(() => asyncPlus100(Promise.reject(fxError)))

examples/napi/index.d.ts

@@ -169,6 +169,7 @@ export function callThreadsafeFunction(callback: (...args: any[]) => any): void
 export function threadsafeFunctionThrowError(cb: (...args: any[]) => any): void
 export function threadsafeFunctionFatalMode(cb: (...args: any[]) => any): void
 export function threadsafeFunctionFatalModeError(cb: (...args: any[]) => any): void
+export function useTokioWithoutAsync(): void
 export function getBuffer(): Buffer
 export function appendBuffer(buf: Buffer): Buffer
 export function getEmptyBuffer(): Buffer

examples/napi/src/lib.rs

@@ -39,4 +39,5 @@ mod string;
 mod symbol;
 mod task;
 mod threadsafe_function;
+mod tokio_outside_async;
 mod typed_array;

examples/napi/src/tokio_outside_async.rs

@@ -0,0 +1,18 @@
+use std::time::Duration;
+use tokio::{sync::oneshot, time::Instant};
+
+#[napi]
+pub fn use_tokio_without_async() {
+  let (sender, receiver) = oneshot::channel();
+  let handle = tokio::task::spawn(async {
+    // If this panics, the test failed.
+    sender.send(true).unwrap();
+  });
+  let start = Instant::now();
+  while !handle.is_finished() {
+    if start.elapsed() > Duration::from_secs(5) {
+      panic!("The future never resolved.");
+    }
+  }
+  assert_eq!(receiver.blocking_recv(), Ok(true));
+}