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// Copyright 2024 the Parley Authors
// SPDX-License-Identifier: Apache-2.0 OR MIT
//! Cache for font data.
#[cfg(feature = "std")]
use super::source::SourceId;
use super::source::{SourceInfo, SourceKind};
#[cfg(feature = "std")]
use hashbrown::HashMap;
use linebender_resource_handle::Blob;
#[cfg(feature = "std")]
use linebender_resource_handle::WeakBlob;
#[cfg(feature = "std")]
use std::{
path::Path,
sync::{Arc, Mutex},
};
/// Options for a [source cache].
///
/// [source cache]: SourceCache
#[derive(Copy, Clone, Default, Debug)]
pub struct SourceCacheOptions {
#[cfg(feature = "std")]
/// If true, the source cache will use a secondary shared cache
/// guaranteeing that all clones will use the same backing store.
///
/// This is useful for ensuring that only one copy of font data is
/// loaded into memory in multi-threaded scenarios.
///
/// The default value is `false`.
pub shared: bool,
}
/// Cache for font data loaded from the file system.
#[derive(Clone, Default)]
pub struct SourceCache {
#[cfg(feature = "std")]
cache: HashMap<SourceId, Entry<Blob<u8>>>,
#[cfg(feature = "std")]
serial: u64,
#[cfg(feature = "std")]
shared: Option<Arc<Mutex<Shared>>>,
}
impl SourceCache {
/// Creates an empty cache with the given [options].
///
/// [options]: SourceCacheOptions
#[cfg_attr(not(feature = "std"), allow(unused))]
pub fn new(options: SourceCacheOptions) -> Self {
#[cfg(feature = "std")]
if options.shared {
return Self {
cache: HashMap::default(),
serial: 0,
shared: Some(Arc::new(Mutex::new(Shared::default()))),
};
}
Self::default()
}
/// Creates an empty cache that is suitable for multi-threaded use.
///
/// A cache created with this function maintains a synchronized internal
/// store that is shared among all clones.
///
/// This is the same as calling [`SourceCache::new`] with an options
/// struct where `shared = true`.
#[cfg(feature = "std")]
pub fn new_shared() -> Self {
Self {
cache: HashMap::default(),
serial: 0,
shared: Some(Arc::new(Mutex::new(Shared::default()))),
}
}
/// Turns an unshared cache into a shared cache that can used to ensure that fonts only get loaded once
/// even when they are loaded across multiple threads.
#[cfg(feature = "std")]
pub fn make_shared(&mut self) {
if self.shared.is_none() {
self.shared = Some(Arc::new(Mutex::new(Shared::from_local(&self.cache))));
}
}
/// Returns the [blob] for the given font data, attempting to load
/// it from the file system if not already present.
///
/// Returns `None` if loading failed.
///
/// [blob]: Blob
pub fn get(&mut self, source: &SourceInfo) -> Option<Blob<u8>> {
match &source.kind {
SourceKind::Memory(memory) => Some(memory.clone()),
#[cfg(feature = "std")]
SourceKind::Path(path) => {
use hashbrown::hash_map::Entry as HashEntry;
match self.cache.entry(source.id()) {
HashEntry::Vacant(vacant) => {
if let Some(mut shared) =
self.shared.as_ref().and_then(|shared| shared.lock().ok())
{
// If we have a backing cache, try to load it there first
// and then propagate the result here.
if let Some(blob) = shared.get(source.id(), path) {
vacant.insert(Entry::Loaded(EntryData {
font_data: blob.clone(),
serial: self.serial,
}));
Some(blob)
} else {
vacant.insert(Entry::Failed);
None
}
} else {
// Otherwise, load it ourselves.
if let Some(blob) = load_blob(path) {
vacant.insert(Entry::Loaded(EntryData {
font_data: blob.clone(),
serial: self.serial,
}));
Some(blob)
} else {
vacant.insert(Entry::Failed);
None
}
}
}
HashEntry::Occupied(mut occupied) => {
let entry = occupied.get_mut();
match entry {
Entry::Loaded(data) => {
data.serial = self.serial;
Some(data.font_data.clone())
}
Entry::Failed => None,
}
}
}
}
}
}
/// Removes all cached blobs that have not been accessed in the last
/// `max_age` times `prune` has been called.
#[cfg_attr(not(feature = "std"), allow(unused))]
pub fn prune(&mut self, max_age: u64, prune_failed: bool) {
#[cfg(feature = "std")]
{
self.cache.retain(|_, entry| match entry {
Entry::Failed => !prune_failed,
Entry::Loaded(data) => self.serial.saturating_sub(data.serial) < max_age,
});
self.serial = self.serial.saturating_add(1);
}
}
}
/// Shared backing store for a font data cache.
#[cfg(feature = "std")]
#[derive(Default)]
struct Shared {
cache: HashMap<SourceId, Entry<WeakBlob<u8>>>,
}
#[cfg(feature = "std")]
impl Shared {
/// Bootstrap a shared cache from a local one
fn from_local(unshared: &HashMap<SourceId, Entry<Blob<u8>>>) -> Self {
let shared_cache: HashMap<SourceId, Entry<WeakBlob<u8>>> = unshared
.iter()
.map(|(key, value)| (*key, value.into()))
.collect();
Self {
cache: shared_cache,
}
}
pub fn get(&mut self, id: SourceId, path: &Path) -> Option<Blob<u8>> {
use hashbrown::hash_map::Entry as HashEntry;
match self.cache.entry(id) {
HashEntry::Vacant(vacant) => {
if let Some(blob) = load_blob(path) {
vacant.insert(Entry::Loaded(EntryData {
font_data: blob.clone().downgrade(),
serial: 0,
}));
Some(blob)
} else {
vacant.insert(Entry::Failed);
None
}
}
HashEntry::Occupied(mut occupied) => {
let entry = occupied.get_mut();
match entry {
Entry::Loaded(data) => {
if let Some(blob) = data.font_data.upgrade() {
// The weak ref is still valid.
Some(blob)
} else if let Some(blob) = load_blob(path) {
// Otherwise, try to reload it.
data.font_data = blob.downgrade();
Some(blob)
} else {
// We failed for some reason.. don't try again.
*entry = Entry::Failed;
None
}
}
Entry::Failed => None,
}
}
}
}
}
#[cfg(feature = "std")]
#[derive(Clone, Default)]
enum Entry<T> {
Loaded(EntryData<T>),
#[default]
Failed,
}
#[cfg(feature = "std")]
#[derive(Clone)]
struct EntryData<T> {
font_data: T,
serial: u64,
}
#[cfg(feature = "std")]
impl<T> From<&Entry<Blob<T>>> for Entry<WeakBlob<T>> {
fn from(value: &Entry<Blob<T>>) -> Self {
match value {
Entry::Loaded(entry_data) => Self::Loaded(EntryData {
font_data: entry_data.font_data.downgrade(),
serial: entry_data.serial,
}),
Entry::Failed => Self::Failed,
}
}
}
#[cfg(feature = "std")]
pub(crate) fn load_blob(path: &Path) -> Option<Blob<u8>> {
let file = std::fs::File::open(path).ok()?;
let mapped = unsafe { memmap2::Mmap::map(&file).ok()? };
Some(Blob::new(Arc::new(mapped)))
}