reactive_graph/effect/

render_effect.rs

use crate::{
    channel::channel,
    effect::inner::EffectInner,
    graph::{
        AnySubscriber, ReactiveNode, SourceSet, Subscriber, ToAnySubscriber,
        WithObserver,
    },
    owner::Owner,
};
use any_spawner::Executor;
use futures::StreamExt;
use or_poisoned::OrPoisoned;
use std::{
    fmt::Debug,
    mem,
    sync::{Arc, RwLock, Weak},
};

/// A render effect is similar to an [`Effect`](super::Effect), but with two key differences:
/// 1. Its first run takes place immediately and synchronously: for example, if it is being used to
///    drive a user interface, it will run during rendering, not on the next tick after rendering.
///    (Hence “render effect.”)
/// 2. It is canceled when the `RenderEffect` itself is dropped, rather than being stored in the
///    reactive system and canceled when the `Owner` cleans up.
///
/// Unless you are implementing a rendering framework, or require one of these two characteristics,
/// it is unlikely you will use render effects directly.
///
/// Like an [`Effect`](super::Effect), a render effect runs only with the `effects` feature
/// enabled.
#[must_use = "A RenderEffect will be canceled when it is dropped. Creating a \
              RenderEffect that is not stored in some other data structure or \
              leaked will drop it immediately, and it will not react to \
              changes in signals it reads."]
pub struct RenderEffect<T>
where
    T: 'static,
{
    value: Arc<RwLock<Option<T>>>,
    inner: Arc<RwLock<EffectInner>>,
}

impl<T> Debug for RenderEffect<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("RenderEffect")
            .field("inner", &Arc::as_ptr(&self.inner))
            .finish()
    }
}

impl<T> RenderEffect<T>
where
    T: 'static,
{
    /// Creates a new render effect, which immediately runs `fun`.
    pub fn new(fun: impl FnMut(Option<T>) -> T + 'static) -> Self {
        Self::new_with_value(fun, None)
    }

    /// Creates a new render effect with an initial value.
    pub fn new_with_value(
        fun: impl FnMut(Option<T>) -> T + 'static,
        initial_value: Option<T>,
    ) -> Self {
        fn erased<T>(
            mut fun: Box<dyn FnMut(Option<T>) -> T + 'static>,
            initial_value: Option<T>,
        ) -> RenderEffect<T> {
            let (observer, mut rx) = channel();
            let value = Arc::new(RwLock::new(None::<T>));
            let owner = Owner::new();
            let inner = Arc::new(RwLock::new(EffectInner {
                dirty: false,
                observer,
                sources: SourceSet::new(),
            }));

            let initial_value = cfg!(feature = "effects").then(|| {
                owner.with(|| {
                    inner
                        .to_any_subscriber()
                        .with_observer(|| fun(initial_value))
                })
            });
            *value.write().or_poisoned() = initial_value;

            if cfg!(feature = "effects") {
                Executor::spawn_local({
                    let value = Arc::clone(&value);
                    let subscriber = inner.to_any_subscriber();

                    async move {
                        while rx.next().await.is_some() {
                            if !owner.paused()
                                && subscriber.with_observer(|| {
                                    subscriber.update_if_necessary()
                                })
                            {
                                subscriber.clear_sources(&subscriber);

                                let old_value = mem::take(
                                    &mut *value.write().or_poisoned(),
                                );
                                let new_value = owner.with_cleanup(|| {
                                    subscriber.with_observer(|| fun(old_value))
                                });
                                *value.write().or_poisoned() = Some(new_value);
                            }
                        }
                    }
                });
            }

            RenderEffect { value, inner }
        }

        erased(Box::new(fun), initial_value)
    }

    /// Mutably accesses the current value.
    pub fn with_value_mut<U>(
        &self,
        fun: impl FnOnce(&mut T) -> U,
    ) -> Option<U> {
        self.value.write().or_poisoned().as_mut().map(fun)
    }

    /// Takes the current value, replacing it with `None`.
    pub fn take_value(&self) -> Option<T> {
        self.value.write().or_poisoned().take()
    }
}

impl<T> RenderEffect<T>
where
    T: Send + Sync + 'static,
{
    /// Creates a render effect that will run whether the `effects` feature is enabled or not.
    pub fn new_isomorphic(
        fun: impl FnMut(Option<T>) -> T + Send + Sync + 'static,
    ) -> Self {
        fn erased<T: Send + Sync + 'static>(
            mut fun: Box<dyn FnMut(Option<T>) -> T + Send + Sync + 'static>,
        ) -> RenderEffect<T> {
            let (observer, mut rx) = channel();
            let value = Arc::new(RwLock::new(None::<T>));
            let owner = Owner::new();
            let inner = Arc::new(RwLock::new(EffectInner {
                dirty: false,
                observer,
                sources: SourceSet::new(),
            }));

            let initial_value = owner
                .with(|| inner.to_any_subscriber().with_observer(|| fun(None)));
            *value.write().or_poisoned() = Some(initial_value);

            crate::spawn({
                let value = Arc::clone(&value);
                let subscriber = inner.to_any_subscriber();

                async move {
                    while rx.next().await.is_some() {
                        if !owner.paused()
                            && subscriber.with_observer(|| {
                                subscriber.update_if_necessary()
                            })
                        {
                            subscriber.clear_sources(&subscriber);

                            let old_value =
                                mem::take(&mut *value.write().or_poisoned());
                            let new_value = owner.with_cleanup(|| {
                                subscriber.with_observer(|| fun(old_value))
                            });
                            *value.write().or_poisoned() = Some(new_value);
                        }
                    }
                }
            });

            RenderEffect { value, inner }
        }

        erased(Box::new(fun))
    }
}

impl<T> ToAnySubscriber for RenderEffect<T> {
    fn to_any_subscriber(&self) -> AnySubscriber {
        AnySubscriber(
            Arc::as_ptr(&self.inner) as usize,
            Arc::downgrade(&self.inner) as Weak<dyn Subscriber + Send + Sync>,
        )
    }
}