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Explain EventWriter limits concurrency #11063

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merged 3 commits into from
Dec 24, 2023
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Explain EventWriter limits concurrency #11063

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5e6800d
Explain EventWriter limits concurrency
stepancheg Dec 22, 2023
5675dba
Update crates/bevy_ecs/src/event.rs
stepancheg Dec 22, 2023
217d638
Avoid using generics in doc comments.
james7132 Dec 23, 2023
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12 changes: 11 additions & 1 deletion crates/bevy_ecs/src/event.rs
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Expand Up @@ -407,6 +407,11 @@ impl<E: Event> DerefMut for EventSequence<E> {
}

/// Reads events of type `T` in order and tracks which events have already been read.
///
/// # Concurrency
///
/// Unlike [`EventWriter<T>`], systems with `EventReader<T>` param can be executed concurrently
/// (but not concurrently with `EventWriter<T>` systems for the same event type).
#[derive(SystemParam, Debug)]
pub struct EventReader<'w, 's, E: Event> {
reader: Local<'s, ManualEventReader<E>>,
Expand Down Expand Up @@ -484,7 +489,12 @@ impl<'w, 's, E: Event> EventReader<'w, 's, E> {
/// # bevy_ecs::system::assert_is_system(my_system);
/// ```
///
/// # Limitations
/// # Concurrency
///
/// `EventWriter` param has [`ResMut<Events<T>>`](Events) inside. So two systems declaring `EventWriter<T>` params
/// for the same event type won't be executed concurrently.
///
/// # Untyped events
///
/// `EventWriter` can only send events of one specific type, which must be known at compile-time.
/// This is not a problem most of the time, but you may find a situation where you cannot know
Expand Down