Unverified Commit 9c83e1de authored by bendk's avatar bendk Committed by GitHub
Browse files

Merge pull request #2418 from jhugman/jhugman/2417-remove-send-from-wasm32-future 

Relax `Send` bound for `Future` for wasm32 targets.
parents 80d5ce2b a80080cf

CHANGELOG.md

+3 −0
Original line number Diff line number Diff line
@@ -64,6 +64,9 @@ or use UDL with types from more than one crate. 


- Switching jinja template engine from askama to rinja.



- For `wasm32` build targets, `Future`s do not have to be `Send` ([#2418](https://github.com/mozilla/uniffi-rs/pull/2418)),

  making them compatible with `wasm-bindgen` `Future`s.



### ⚠️ Breaking Changes for external bindings authors ⚠️



- Added the `FfiType::MutReference` variant.

uniffi_core/src/ffi/rustfuture/future.rs

+8 −9
Original line number Diff line number Diff line
@@ -76,7 +76,6 @@ 
//! [`RawWaker`]: https://doc.rust-lang.org/std/task/struct.RawWaker.html



use std::{

    future::Future,

    marker::PhantomData,

    ops::Deref,

    panic,
@@ -85,14 +84,14 @@ use std::{ 
    task::{Context, Poll, Wake},

};



use super::{RustFutureContinuationCallback, RustFuturePoll, Scheduler};

use super::{RustFutureContinuationCallback, RustFuturePoll, Scheduler, UniffiCompatibleFuture};

use crate::{rust_call_with_out_status, FfiDefault, LiftArgsError, LowerReturn, RustCallStatus};



/// Wraps the actual future we're polling

struct WrappedFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -106,7 +105,7 @@ where 
impl<F, T, UT> WrappedFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -186,7 +185,7 @@ where 
unsafe impl<F, T, UT> Send for WrappedFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -196,7 +195,7 @@ where 
pub(super) struct RustFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -212,7 +211,7 @@ where 
impl<F, T, UT> RustFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -267,7 +266,7 @@ where 
impl<F, T, UT> Wake for RustFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{
@@ -302,7 +301,7 @@ pub trait RustFutureFfi<ReturnType>: Send + Sync { 
impl<F, T, UT> RustFutureFfi<T::ReturnType> for RustFuture<F, T, UT>

where

    // See rust_future_new for an explanation of these trait bounds

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    T: LowerReturn<UT> + Send + 'static,

    UT: Send + 'static,

{

uniffi_core/src/ffi/rustfuture/mod.rs

+57 −1
Original line number Diff line number Diff line
@@ -30,6 +30,62 @@ pub enum RustFuturePoll { 
/// to continue progress on the future.

pub type RustFutureContinuationCallback = extern "C" fn(callback_data: u64, RustFuturePoll);



/// This marker trait allows us to put different bounds on the `Future`s we

/// support, based on `#[cfg(..)]` configuration.

///

/// It should not be considered as a part of the public API, and as such as

/// an implementation detail and subject to change.

///

/// It is _not_ intended to be implemented by libray users or bindings

/// implementors.

#[doc(hidden)]

pub trait UniffiCompatibleFuture<T>: Future<Output = T> {}



/// The `Send` bound is required because the Foreign code may call the

/// `rust_future_*` methods from different threads.

#[cfg(not(target_arch = "wasm32"))]

impl<T, F> UniffiCompatibleFuture<T> for F where F: Future<Output = T> + Send {}



/// `Future`'s on WASM32 are not `Send` because it's a single threaded environment.

///

/// # Safety:

///

/// WASM32 is a single threaded environment. However, in a browser there do

/// exist [`WebWorker`][webworker]s which do not share memory or event-loop

/// with the main browser context.

///

/// Communication between contexts is only possible by message passing,

/// using a small number of ['transferable' object types][transferable].

///

/// The most common source of asynchrony in Rust compiled to WASM is

/// [wasm-bindgen's `JsFuture`][jsfuture]. It is not `Send` because:

///

/// 1. `T` and `E` are both `JsValue`

/// 2. `JsValue` may contain `JsFunction`s, either as a function themselves or

///    an object containing functions.

/// 3. Functions cannot be [serialized and sent][transferable] to `WebWorker`s.

///

/// Implementors of binding generators should be able to enumerate the

/// combinations of Rust or JS communicating across different contexts (here

/// using: <->), and in the same context (+) to account for why it is safe

/// for UniFFI to support `Future`s that are not `Send`:

///

/// 1. JS + Rust in the same contexts: polling and waking happens in the same

///    thread, no `Send` is needed.

/// 2. Rust <-> Rust in different contexts: Futures cannot be sent between JS

///    contexts within the same Rust crate (because they are not `Send`).

/// 3. JS <-> Rust in different contexts: the `Promise` are [not transferable

///    between contexts][transferable], so this is impossible.

/// 4. JS <-> JS + Rust, this is possible, but safe since the Future is being

///    driven by JS in the same thread. If a Promise metaphor is desired, then

///    this must be built with JS talking to JS, because 3.

///

/// [webworker]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers

/// [jsfuture]: https://github.com/rustwasm/wasm-bindgen/blob/main/crates/futures/src/lib.rs

/// [transferable]: (https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Transferable_objects

#[cfg(target_arch = "wasm32")]

impl<T, F> UniffiCompatibleFuture<T> for F where F: Future<Output = T> {}



// === Public FFI API ===



/// Create a new [Handle] for a Rust future
@@ -44,7 +100,7 @@ where 
    // since it will move between threads for an indeterminate amount of time as the foreign

    // executor calls polls it and the Rust executor wakes it.  It does not need to by `Sync`,

    // since we synchronize all access to the values.

    F: Future<Output = Result<T, LiftArgsError>> + Send + 'static,

    F: UniffiCompatibleFuture<Result<T, LiftArgsError>> + 'static,

    // T is the output of the Future.  It needs to implement [LowerReturn].  Also it must be Send +

    // 'static for the same reason as F.

    T: LowerReturn<UT> + Send + 'static,