darkfi/bin/app/src/prop/guard.rs

/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2026 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::sync::{
    atomic::{AtomicU32, Ordering},
    Arc,
};

use super::{ModifyAction, PropertyPtr, Role};

static BATCH_ID: AtomicU32 = AtomicU32::new(0);

/// This schedules all property updates to happen at the end of the scope.
/// We can therefore have fine-grained control about when property updates are
/// propagated to the rest of the scenegraph.
///
/// This way we avoid triggering draw updates mid draw, and changes are atomic.
/// For example resizing the content view, will trigger the editbox background to
/// redraw while a current window wide draw is in progress. Since the window draw
/// triggered the change when we submit the draw update, it will be discarded by
/// the editbox bg triggered update. However this update won't have the current
/// rect and will be stale.
///
/// 1. Content draw starts
/// 2. Dependent property triggers and submits editbox bg redraw.
/// 3. Content draw continues and now draws editbox bg with updated rect.
/// 4. Finished content draw's editbox bg update is discarded in favour of #2.
///    However #2 used the pre-updated rect and is now stale.
///
/// We solve the above issue by batching all updates until after the draw call is finished.
/// This also has the unintended side-effect of making draws much faster since they aren't
/// interrupted halfway through by extra compute.
pub struct PropertyAtomicGuard {
    pub batch_id: BatchGuardId,
    updates: Vec<(PropertyPtr, Role, ModifyAction)>,
    end_batch: Option<BatchGuardCb>,
    parent: Option<BatchGuardPtr>,
}

impl PropertyAtomicGuard {
    pub fn new(start_batch: BatchGuardCb, end_batch: BatchGuardCb) -> Self {
        let batch_id = BATCH_ID.fetch_add(1, Ordering::Relaxed);
        start_batch(batch_id);
        Self { batch_id, updates: vec![], end_batch: Some(end_batch), parent: None }
    }

    /// Should only be used when there's an explicit end_batch() called manually at the end
    /// of the context.
    /// You probably mostly want to either `batch.spawn()` from an existing batch
    /// or use `render_api.make_guard()`.
    pub fn none() -> Self {
        Self::new(Box::new(|_| {}), Box::new(|_| {}))
    }

    pub(super) fn add(&mut self, prop: PropertyPtr, role: Role, action: ModifyAction) {
        self.updates.push((prop, role, action));
    }
}

impl Drop for PropertyAtomicGuard {
    fn drop(&mut self) {
        let guard = Arc::new(BatchGuard {
            id: self.batch_id,
            end_batch: self.end_batch.take(),
            _parent: self.parent.take(),
        });
        for (prop, role, action) in std::mem::take(&mut self.updates) {
            prop.on_modify.notify((role, action, guard.clone()));
        }
    }
}

impl std::fmt::Debug for PropertyAtomicGuard {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "@{:?}", self.batch_id)
    }
}

pub type BatchGuardId = u32;
type BatchGuardCb = Box<dyn FnOnce(BatchGuardId) + Send + Sync>;
pub type BatchGuardPtr = Arc<BatchGuard>;

pub struct BatchGuard {
    pub id: BatchGuardId,
    end_batch: Option<BatchGuardCb>,
    _parent: Option<BatchGuardPtr>,
}

impl BatchGuard {
    pub fn spawn(self: &Arc<Self>) -> PropertyAtomicGuard {
        PropertyAtomicGuard {
            batch_id: self.id,
            updates: vec![],
            end_batch: Some(Box::new(|_| {})),
            parent: Some(self.clone()),
        }
    }
}

impl Drop for BatchGuard {
    fn drop(&mut self) {
        let end_batch = self.end_batch.take().unwrap();
        end_batch(self.id);
    }
}

impl std::fmt::Debug for BatchGuard {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        f.debug_struct("BatchGuard").field("id", &self.id).finish()
    }
}