rust_widgets 2.1.0

// SPDX-FileCopyrightText: Copyright (c) 2026 Mike Li/Mikewolfli/Wei Li(mikewolfli@163.com)
// SPDX-License-Identifier: MIT

use crate::compat::Mutex;
use alloc::sync::Arc;
/// Types that can be recycled through an [`ObjectPool`].
///
/// The bound is `Default + Clone`, where `Default` supplies the state for a
/// freshly minted object and `Clone` lets a pool prototype be copied. `Clone` is
/// required even though pooling reuses values in place rather than cloning them.
/// Reuse is only observably safe because [`Poolable::reset`] is expected to wipe
/// any per-use state.
pub trait Poolable: Default + Clone {
    /// Restores `self` to the same logical state as `Self::default()`.
    ///
    /// Called by the pool both when an object is handed back and again when it is
    /// handed out, so implementations are expected to be idempotent and cheap.
    /// Capacity-like resources (allocated buffers, reserved slots) are usually
    /// *kept* rather than freed; only the logical contents must be discarded.
    fn reset(&mut self);
}
/// Tuning parameters for [`ObjectPool`].
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct PoolConfig {
    /// Number of reusable objects created eagerly by [`ObjectPool::new`]. Also the
    /// initial heap reservation for the backing `Vec`. Zero is allowed.
    pub initial_size: usize,
    /// Upper bound on how many objects [`ObjectPool::release`] keeps in the pool.
    /// Objects handed back once the pool is this full are dropped, so the count
    /// reported by [`ObjectPool::available`] never exceeds it.
    pub max_size: usize,
    /// Retained for compatibility and currently *unused*: `ObjectPool` grows
    /// lazily by allocating a `Default` value on demand, so no capacity is
    /// pre-computed from this factor.
    pub growth_factor: f32,
}
impl Default for PoolConfig {
    fn default() -> Self {
        Self { initial_size: 16, max_size: 1024, growth_factor: 1.5 }
    }
}
/// A recycling pool of mutable objects of a single type.
///
/// Unlike a general-purpose allocator ([`crate::memory::allocators`]), this is a
/// *fixed-shape* pool: every slot holds an already-constructed `T`, and reuse
/// means calling [`Poolable::reset`] rather than re-running a constructor.
///
/// The pool never blocks and never fails. When it runs dry, [`Self::acquire`]
/// silently manufactures a fresh `T::default()` instead of growing a pool of
/// entries, so over-drawing degrades to plain allocation rather than an error.
///
/// Not thread-safe on its own; wrap it in [`SharedPool`] or an external lock to
/// share it between threads.
pub struct ObjectPool<T: Poolable> {
    pool: Vec<T>,
    config: PoolConfig,
    allocated: usize,
}
impl<T: Poolable> ObjectPool<T> {
    /// Creates a pool pre-filled with `config.initial_size` objects, each produced
    /// by `T::default()`.
    ///
    /// This is a constructor, not an allocation-free one: `initial_size` objects
    /// exist (and are initialised) immediately, so large `T` values make this
    /// expensive.
    pub fn new(config: PoolConfig) -> Self {
        let mut pool = Vec::with_capacity(config.initial_size);
        for _ in 0..config.initial_size {
            pool.push(T::default());
        }
        Self { pool, config, allocated: 0 }
    }
    /// Takes an object out of the pool, resetting it before the caller sees it.
    ///
    /// If the pool is empty a brand new `T::default()` is returned instead of
    /// blocking — the call never fails. Reused objects have already had
    /// [`Poolable::reset`] applied, so callers never observe leftover data from
    /// the previous user; whether memory is *zeroed* depends entirely on that
    /// implementation.
    pub fn acquire(&mut self) -> T {
        if let Some(mut obj) = self.pool.pop() {
            obj.reset();
            self.allocated += 1;
            obj
        } else {
            self.allocated += 1;
            T::default()
        }
    }
    /// Returns an object to the pool for reuse.
    ///
    /// The object is reset first, then kept only while the pool holds fewer than
    /// `max_size` objects; otherwise it is dropped and the memory is freed. The
    /// `allocated` counter is decremented (saturating at zero) even when the
    /// object is discarded, so a release without a matching acquire does not make
    /// the counter wrap.
    pub fn release(&mut self, mut obj: T) {
        obj.reset();
        if self.pool.len() < self.config.max_size {
            self.pool.push(obj);
        }
        self.allocated = self.allocated.saturating_sub(1);
    }
    /// Number of objects currently sitting in the pool ready to be handed out.
    /// Bounded by [`PoolConfig::max_size`].
    pub fn available(&self) -> usize {
        self.pool.len()
    }
    /// Net number of acquisitions that have not yet been released.
    ///
    /// This is a running counter, not a measurement of live objects: an acquire
    /// that had to construct a fresh `T` still increments it, and releasing an
    /// object that came from outside the pool still decrements it. It can
    /// therefore disagree with the number of objects the caller can account for.
    pub fn allocated(&self) -> usize {
        self.allocated
    }
    /// Current heap capacity of the pool's backing storage, in objects.
    ///
    /// This is a `Vec` capacity, so it is at least [`Self::available`] and can be
    /// larger after objects were dropped on release.
    pub fn capacity(&self) -> usize {
        self.pool.capacity()
    }
    /// Drops every pooled object and resets the `allocated` counter to zero.
    ///
    /// Objects currently checked out by callers are unaffected; the pool simply
    /// forgets about them, so later [`Self::release`] calls will decrement the
    /// counter from its reset value.
    pub fn clear(&mut self) {
        self.pool.clear();
        self.allocated = 0;
    }
    /// Shrinks the pool's backing storage to fit its current contents.
    ///
    /// Frees heap memory but does not change how many objects are pooled; the pool
    /// will simply reallocate on the next [`Self::release`].
    pub fn shrink_to_fit(&mut self) {
        self.pool.shrink_to_fit();
    }
}
impl<T: Poolable> Default for ObjectPool<T> {
    fn default() -> Self {
        Self::new(PoolConfig::default())
    }
}
/// A reference-counted, thread-safe handle to an [`ObjectPool`].
///
/// Cloning a `SharedPool` is cheap and yields another handle onto the *same* pool,
/// so multiple threads or widgets can share one cache. All operations take an
/// internal mutex; on a poisoned lock the inner value is recovered instead of
/// panicking. Requires `T: Send` because pooled objects travel between threads.
pub struct SharedPool<T: Poolable + Send> {
    pool: Arc<Mutex<ObjectPool<T>>>,
}
impl<T: Poolable + Send> SharedPool<T> {
    /// Creates a new shared pool around a freshly built [`ObjectPool`].
    pub fn new(config: PoolConfig) -> Self {
        Self { pool: Arc::new(Mutex::new(ObjectPool::new(config))) }
    }
    /// Takes an object from the shared pool, blocking only for the duration of the
    /// internal mutex.
    ///
    /// Same semantics as [`ObjectPool::acquire`]: the pool never runs out, a fresh
    /// `T::default()` is substituted when empty, and the value is reset before it
    /// is returned.
    pub fn acquire(&self) -> T {
        self.pool.lock().unwrap_or_else(|e| e.into_inner()).acquire()
    }
    /// Returns an object to the shared pool; see [`ObjectPool::release`] for the
    /// reset and `max_size` behaviour.
    pub fn release(&self, obj: T) {
        self.pool.lock().unwrap_or_else(|e| e.into_inner()).release(obj);
    }
    /// Captures a consistent snapshot of the pool's counters under a single lock.
    ///
    /// Cheap enough to poll for diagnostics. Like any snapshot it can be stale as
    /// soon as it is returned if other threads are acquiring or releasing.
    pub fn stats(&self) -> PoolStats {
        let pool = self.pool.lock().unwrap_or_else(|e| e.into_inner());
        PoolStats {
            available: pool.available(),
            allocated: pool.allocated(),
            capacity: pool.capacity(),
        }
    }
}
impl<T: Poolable + Send> Clone for SharedPool<T> {
    fn clone(&self) -> Self {
        Self { pool: Arc::clone(&self.pool) }
    }
}
impl<T: Poolable + Send> Default for SharedPool<T> {
    fn default() -> Self {
        Self::new(PoolConfig::default())
    }
}
/// A snapshot of pool occupancy, as returned by [`SharedPool::stats`].
#[derive(Debug, Clone, Copy)]
pub struct PoolStats {
    /// Objects idle in the pool, ready to be acquired (bounded by
    /// [`PoolConfig::max_size`]).
    pub available: usize,
    /// Net acquisitions not yet released; see [`ObjectPool::allocated`].
    pub allocated: usize,
    /// Heap capacity of the pool's backing storage, in objects.
    pub capacity: usize,
}
/// A heterogenous registry of [`SharedPool`]s keyed only by type.
///
/// Lets an application keep its pools in one place and drop them together. The
/// registry does not own the pools: it stores a `SharedPool` clone per entry, so
/// outstanding handles stay valid after the manager is dropped or cleared.
pub struct PoolManager {
    pools: Vec<Box<dyn std::any::Any + Send>>,
}
impl PoolManager {
    /// Creates an empty registry.
    pub fn new() -> Self {
        Self { pools: Vec::new() }
    }
    /// Creates a new pool for `T`, records it in the registry, and returns a
    /// handle to it.
    ///
    /// Types are not deduplicated by `T`: calling this twice for the same `T`
    /// registers and returns two independent pools, so callers that want a single
    /// cache per type must track that themselves.
    pub fn register<T: Poolable + Send + 'static>(&mut self, config: PoolConfig) -> SharedPool<T> {
        let pool = SharedPool::new(config);
        self.pools.push(Box::new(pool.clone()));
        pool
    }
    /// Forgets every registered pool.
    ///
    /// The pools themselves are only freed if no other `SharedPool` handle
    /// remains; live handles keep working and keep sharing the same state.
    pub fn clear_all(&mut self) {
        self.pools.clear();
    }
}
crate::impl_default_via_new!(PoolManager);
/// A pool of equally sized byte buffers.
///
/// Unlike [`ObjectPool`] this is a *fixed-size buffer pool*: only buffers whose
/// capacity exactly equals [`Self::buffer_size`] are retained, so the pool hands
/// out uniformly shaped allocations and never has to grow one. Not thread-safe;
/// use one pool per thread or guard it externally.
pub struct BufferPool {
    buffers: Vec<Vec<u8>>,
    buffer_size: usize,
    max_buffers: usize,
}
impl BufferPool {
    /// Creates a pool of `buffer_size`-byte buffers, pre-allocating `initial_count`
    /// of them.
    ///
    /// `buffer_size` is the exact capacity the pool recycles; `max_buffers` caps
    /// how many [`Self::release`] will keep. Both bounds are inclusive and may be
    /// zero. Every pre-allocated buffer is zero-filled.
    pub fn new(buffer_size: usize, initial_count: usize, max_buffers: usize) -> Self {
        let mut buffers = Vec::with_capacity(initial_count);
        for _ in 0..initial_count {
            buffers.push(vec![0u8; buffer_size]);
        }
        Self { buffers, buffer_size, max_buffers }
    }
    /// Hands out a buffer of exactly [`Self::buffer_size`] bytes.
    ///
    /// Never blocks and never fails: when the pool is empty a fresh zero-filled
    /// buffer is allocated. Recycling does *not* wipe the bytes — the returned
    /// buffer still holds whatever the previous user wrote, though its length is
    /// the full `buffer_size`. Callers must treat the contents as garbage, or use
    /// [`Self::acquire_sized`], which zeroes the range it returns.
    pub fn acquire(&mut self) -> Vec<u8> {
        self.buffers.pop().unwrap_or_else(|| vec![0u8; self.buffer_size])
    }
    /// Hands out a zero-filled buffer of exactly `size` bytes.
    ///
    /// Sizes at or below [`Self::buffer_size`] reuse a pooled buffer, so the whole
    /// `size` range is zeroed before returning and the capacity may still exceed
    /// `size`. Larger sizes are allocated fresh, unpooled, and are discarded on
    /// release because their capacity no longer matches the pool — repeatedly
    /// asking for oversized buffers gets no reuse at all.
    pub fn acquire_sized(&mut self, size: usize) -> Vec<u8> {
        if size <= self.buffer_size {
            let mut buf = self.acquire();
            buf.clear();
            buf.resize(size, 0);
            buf
        } else {
            vec![0u8; size]
        }
    }
    /// Returns a buffer for reuse.
    //
    // The buffer is kept only when its capacity is exactly `buffer_size` and the
    // pool is below `max_buffers`; otherwise it is dropped and freed.
    //
    /// Returning a buffer whose length is non-zero is fine: it is cleared first,
    /// so recycled buffers always leave the pool empty-but-capacity-sized. Because
    /// the check is on `capacity`, a buffer obtained from [`Self::acquire_sized`]
    /// with `size < buffer_size` is still accepted, but an oversized one is not.
    pub fn release(&mut self, mut buffer: Vec<u8>) {
        if buffer.capacity() == self.buffer_size && self.buffers.len() < self.max_buffers {
            buffer.clear();
            self.buffers.push(buffer);
        }
    }
    /// Number of pooled buffers ready to be handed out; bounded by `max_buffers`.
    pub fn available(&self) -> usize {
        self.buffers.len()
    }
    /// Exact buffer capacity the pool pools and hands out, in bytes.
    pub fn buffer_size(&self) -> usize {
        self.buffer_size
    }
    /// Drops every pooled buffer, freeing their memory.
    ///
    /// Buffers already checked out by callers are unaffected and can still be
    /// released back into the now-empty pool.
    pub fn clear(&mut self) {
        self.buffers.clear();
    }
}
impl Default for BufferPool {
    fn default() -> Self {
        Self::new(4096, 4, 64)
    }
}
/// A pool of reusable, empty `String`s with pre-reserved capacity.
///
/// A fixed-size style pool: only strings whose capacity is at least
/// the pool's default capacity are retained, which keeps reallocation out of the
/// steady state. Acquired strings are always empty. Not thread-safe.
pub struct StringPool {
    strings: Vec<String>,
    default_capacity: usize,
    max_strings: usize,
}
impl StringPool {
    /// Creates a pool reserving `default_capacity` bytes per string, with
    /// `initial_count` strings pre-created.
    ///
    /// `max_strings` caps how many [`Self::release`] will keep. Note that a
    /// `default_capacity` of zero makes the capacity check in `release` always
    /// succeed, so effectively every returned string is kept up to `max_strings`.
    pub fn new(default_capacity: usize, initial_count: usize, max_strings: usize) -> Self {
        let mut strings = Vec::with_capacity(initial_count);
        for _ in 0..initial_count {
            strings.push(String::with_capacity(default_capacity));
        }
        Self { strings, default_capacity, max_strings }
    }
    /// Hands out an empty `String`, reusing a pooled one when possible.
    ///
    /// Never blocks and never fails; allocates a fresh `String` when the pool is
    /// empty. The returned string always has zero length, and its capacity is at
    /// least `default_capacity` — but callers must not assume a particular
    /// capacity, since pooled strings may be larger.
    pub fn acquire(&mut self) -> String {
        self.strings.pop().unwrap_or_else(|| String::with_capacity(self.default_capacity))
    }
    /// Returns a string for reuse.
    ///
    /// The string is cleared (contents discarded, capacity kept) and pooled only
    /// if its capacity is at least `default_capacity` and the pool is below
    /// `max_strings`; otherwise it is dropped. Contents are never preserved, so
    /// callers cannot hand off data through the pool.
    pub fn release(&mut self, mut s: String) {
        s.clear();
        if s.capacity() >= self.default_capacity && self.strings.len() < self.max_strings {
            self.strings.push(s);
        }
    }
    /// Number of strings currently pooled; bounded by `max_strings`.
    pub fn available(&self) -> usize {
        self.strings.len()
    }
    /// Drops every pooled string, freeing their memory. Strings already handed out
    /// remain valid and may still be released back.
    pub fn clear(&mut self) {
        self.strings.clear();
    }
}
impl Default for StringPool {
    fn default() -> Self {
        Self::new(64, 8, 128)
    }
}
/// A pool of reusable, empty `Vec<T>`s with pre-reserved capacity.
///
/// The generic analogue of [`BufferPool`] and [`StringPool`]: it recycles
/// containers rather than their element types, keeping each vector's heap
/// allocation alive across acquires. Only vectors whose capacity is at least
/// `default_capacity` are retained. Not thread-safe.
pub struct VecPool<T> {
    vecs: Vec<Vec<T>>,
    default_capacity: usize,
    max_vecs: usize,
}
impl<T> VecPool<T> {
    /// Creates a pool of vectors with `default_capacity` reserved elements each,
    /// pre-creating `initial_count` of them.
    ///
    /// Nothing is written into the vectors, so `T` needs no `Default` bound; the
    /// capacity is merely reserved. `max_vecs` caps how many [`Self::release`]
    /// will keep.
    pub fn new(default_capacity: usize, initial_count: usize, max_vecs: usize) -> Self {
        let mut vecs = Vec::with_capacity(initial_count);
        for _ in 0..initial_count {
            vecs.push(Vec::with_capacity(default_capacity));
        }
        Self { vecs, default_capacity, max_vecs }
    }
    /// Hands out an empty `Vec<T>`, reusing a pooled one when possible.
    ///
    /// Never blocks and never fails; allocates a fresh vector when the pool is
    /// empty. The result is guaranteed empty, and its capacity is at least
    /// `default_capacity` when it came from the pool's initial fill. No element is
    /// ever constructed and no memory is cleared, so `T` need not be zeroable.
    pub fn acquire(&mut self) -> Vec<T> {
        self.vecs.pop().unwrap_or_else(|| Vec::with_capacity(self.default_capacity))
    }
    /// Returns a vector for reuse.
    ///
    /// The vector is cleared first, dropping any contained `T` values, then pooled
    /// only if its capacity is at least `default_capacity` and the pool is below
    /// `max_vecs`; otherwise it is dropped and freed. Clearing keeps the heap
    /// allocation but always discards the elements, so the pool must not be used to
    /// pass data between owners.
    pub fn release(&mut self, mut v: Vec<T>) {
        v.clear();
        if v.capacity() >= self.default_capacity && self.vecs.len() < self.max_vecs {
            self.vecs.push(v);
        }
    }
    /// Number of vectors currently pooled; bounded by `max_vecs`.
    pub fn available(&self) -> usize {
        self.vecs.len()
    }
    /// Drops every pooled vector, freeing their element storage. Vectors already
    /// handed out remain valid and may still be released back.
    pub fn clear(&mut self) {
        self.vecs.clear();
    }
}
impl<T> Default for VecPool<T> {
    fn default() -> Self {
        Self::new(16, 4, 64)
    }
}
#[cfg(test)]
mod tests {
    use super::*;
    #[derive(Default, Clone)]
    struct TestObject {
        value: i32,
        data: Vec<u8>,
    }
    impl Poolable for TestObject {
        fn reset(&mut self) {
            self.value = 0;
            self.data.clear();
        }
    }
    #[test]
    fn test_object_pool() {
        let mut pool: ObjectPool<TestObject> =
            ObjectPool::new(PoolConfig { initial_size: 4, max_size: 8, growth_factor: 1.5 });
        assert_eq!(pool.available(), 4);
        let obj1 = pool.acquire();
        assert_eq!(pool.allocated(), 1);
        pool.release(obj1);
        assert_eq!(pool.available(), 4);
    }
    #[test]
    fn test_buffer_pool() {
        let mut pool = BufferPool::new(1024, 2, 4);
        let buf1 = pool.acquire();
        assert_eq!(buf1.len(), 1024);
        pool.release(buf1);
        assert_eq!(pool.available(), 2);
    }
}