i_slint_core/
sharedvector.rs

1// Copyright © SixtyFPS GmbH <info@slint.dev>
2// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
3
4//! module for the SharedVector and related things
5#![allow(unsafe_code)]
6#![warn(missing_docs)]
7use core::fmt::Debug;
8use core::mem::MaybeUninit;
9use core::ops::Deref;
10use core::ptr::NonNull;
11
12use portable_atomic as atomic;
13
14#[repr(C)]
15struct SharedVectorHeader {
16    refcount: atomic::AtomicIsize,
17    size: usize,
18    capacity: usize,
19}
20
21#[repr(C)]
22struct SharedVectorInner<T> {
23    header: SharedVectorHeader,
24    data: MaybeUninit<T>,
25}
26
27fn compute_inner_layout<T>(capacity: usize) -> core::alloc::Layout {
28    core::alloc::Layout::new::<SharedVectorHeader>()
29        .extend(core::alloc::Layout::array::<T>(capacity).unwrap())
30        .unwrap()
31        .0
32}
33
34unsafe fn drop_inner<T>(mut inner: NonNull<SharedVectorInner<T>>) {
35    debug_assert_eq!(inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed), 0);
36    let data_ptr = inner.as_mut().data.as_mut_ptr();
37    for x in 0..inner.as_ref().header.size {
38        core::ptr::drop_in_place(data_ptr.add(x));
39    }
40    alloc::alloc::dealloc(
41        inner.as_ptr() as *mut u8,
42        compute_inner_layout::<T>(inner.as_ref().header.capacity),
43    )
44}
45
46/// Allocate the memory for the SharedVector with the given capacity. Return the inner with size and refcount set to 1
47fn alloc_with_capacity<T>(capacity: usize) -> NonNull<SharedVectorInner<T>> {
48    let ptr = unsafe { ::alloc::alloc::alloc(compute_inner_layout::<T>(capacity)) };
49    assert!(!ptr.is_null(), "allocation of {capacity:?} bytes failed");
50    unsafe {
51        core::ptr::write(
52            ptr as *mut SharedVectorHeader,
53            SharedVectorHeader { refcount: 1.into(), size: 0, capacity },
54        );
55    }
56    NonNull::new(ptr).unwrap().cast()
57}
58
59/// Return a new capacity suitable for this vector
60/// Loosely based on alloc::raw_vec::RawVec::grow_amortized.
61fn capacity_for_grow(current_cap: usize, required_cap: usize, elem_size: usize) -> usize {
62    if current_cap >= required_cap {
63        return current_cap;
64    }
65    let cap = core::cmp::max(current_cap * 2, required_cap);
66    let min_non_zero_cap = if elem_size == 1 {
67        8
68    } else if elem_size <= 1024 {
69        4
70    } else {
71        1
72    };
73    core::cmp::max(min_non_zero_cap, cap)
74}
75
76#[repr(C)]
77/// SharedVector holds a reference-counted read-only copy of `[T]`.
78pub struct SharedVector<T> {
79    inner: NonNull<SharedVectorInner<T>>,
80}
81
82// Safety: We use atomic reference counting, and if T is Send and Sync, we can send the vector to another thread
83unsafe impl<T: Send + Sync> Send for SharedVector<T> {}
84// Safety: We use atomic reference counting, and if T is Send and Sync, we can access the vector from multiple threads
85unsafe impl<T: Send + Sync> Sync for SharedVector<T> {}
86
87impl<T> Drop for SharedVector<T> {
88    fn drop(&mut self) {
89        unsafe {
90            if self
91                .inner
92                .cast::<SharedVectorHeader>()
93                .as_ref()
94                .refcount
95                .load(atomic::Ordering::Relaxed)
96                < 0
97            {
98                return;
99            }
100            if self.inner.as_ref().header.refcount.fetch_sub(1, atomic::Ordering::SeqCst) == 1 {
101                drop_inner(self.inner)
102            }
103        }
104    }
105}
106
107impl<T> Clone for SharedVector<T> {
108    fn clone(&self) -> Self {
109        unsafe {
110            if self
111                .inner
112                .cast::<SharedVectorHeader>()
113                .as_ref()
114                .refcount
115                .load(atomic::Ordering::Relaxed)
116                > 0
117            {
118                self.inner.as_ref().header.refcount.fetch_add(1, atomic::Ordering::SeqCst);
119            }
120            SharedVector { inner: self.inner }
121        }
122    }
123}
124
125impl<T> SharedVector<T> {
126    /// Create a new empty array with a pre-allocated capacity in number of items
127    pub fn with_capacity(capacity: usize) -> Self {
128        Self { inner: alloc_with_capacity(capacity) }
129    }
130
131    fn as_ptr(&self) -> *const T {
132        unsafe { self.inner.as_ref().data.as_ptr() }
133    }
134
135    /// Number of elements in the array
136    pub fn len(&self) -> usize {
137        unsafe { self.inner.cast::<SharedVectorHeader>().as_ref().size }
138    }
139
140    /// Return true if the SharedVector is empty
141    pub fn is_empty(&self) -> bool {
142        self.len() == 0
143    }
144
145    /// Return a slice to the array
146    pub fn as_slice(&self) -> &[T] {
147        if self.is_empty() {
148            &[]
149        } else {
150            // Safety: When len > 0, we know that the pointer holds an array of the size of len
151            unsafe { core::slice::from_raw_parts(self.as_ptr(), self.len()) }
152        }
153    }
154
155    /// Returns the number of elements the vector can hold without reallocating, when not shared
156    fn capacity(&self) -> usize {
157        unsafe { self.inner.cast::<SharedVectorHeader>().as_ref().capacity }
158    }
159}
160
161impl<T: Clone> SharedVector<T> {
162    /// Create a SharedVector from a slice
163    pub fn from_slice(slice: &[T]) -> SharedVector<T> {
164        Self::from(slice)
165    }
166
167    /// Ensure that the reference count is 1 so the array can be changed.
168    /// If that's not the case, the array will be cloned
169    fn detach(&mut self, new_capacity: usize) {
170        let is_shared =
171            unsafe { self.inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed) } != 1;
172        if !is_shared && new_capacity <= self.capacity() {
173            return;
174        }
175        let mut new_array = SharedVector::with_capacity(new_capacity);
176        core::mem::swap(&mut self.inner, &mut new_array.inner);
177        let mut size = 0;
178        for x in new_array.into_iter() {
179            assert_ne!(size, new_capacity);
180            unsafe {
181                core::ptr::write(self.inner.as_mut().data.as_mut_ptr().add(size), x);
182                size += 1;
183                self.inner.as_mut().header.size = size;
184            }
185            if size == new_capacity {
186                break;
187            }
188        }
189    }
190
191    /// Return a mutable slice to the array. If the array was shared, this will make a copy of the array.
192    pub fn make_mut_slice(&mut self) -> &mut [T] {
193        self.detach(self.len());
194        unsafe { core::slice::from_raw_parts_mut(self.as_ptr() as *mut T, self.len()) }
195    }
196
197    /// Add an element to the array. If the array was shared, this will make a copy of the array.
198    pub fn push(&mut self, value: T) {
199        self.detach(capacity_for_grow(self.capacity(), self.len() + 1, core::mem::size_of::<T>()));
200        unsafe {
201            core::ptr::write(
202                self.inner.as_mut().data.as_mut_ptr().add(self.inner.as_mut().header.size),
203                value,
204            );
205            self.inner.as_mut().header.size += 1;
206        }
207    }
208
209    /// Removes last element from the array and returns it.
210    /// If the array was shared, this will make a copy of the array.
211    pub fn pop(&mut self) -> Option<T> {
212        if self.is_empty() {
213            None
214        } else {
215            self.detach(self.len());
216            unsafe {
217                self.inner.as_mut().header.size -= 1;
218                Some(core::ptr::read(self.inner.as_mut().data.as_mut_ptr().add(self.len())))
219            }
220        }
221    }
222
223    /// Resize the array to the given size.
224    /// If the array was smaller new elements will be initialized with the value.
225    /// If the array was bigger, extra elements will be discarded
226    ///
227    /// ```
228    /// use i_slint_core::SharedVector;
229    /// let mut shared_vector = SharedVector::<u32>::from_slice(&[1, 2, 3]);
230    /// shared_vector.resize(5, 8);
231    /// assert_eq!(shared_vector.as_slice(), &[1, 2, 3, 8, 8]);
232    /// shared_vector.resize(2, 0);
233    /// assert_eq!(shared_vector.as_slice(), &[1, 2]);
234    /// ```
235    pub fn resize(&mut self, new_len: usize, value: T) {
236        if self.len() == new_len {
237            return;
238        }
239        self.detach(new_len);
240        // Safety: detach ensured that the array is not shared.
241        let inner = unsafe { self.inner.as_mut() };
242
243        if inner.header.size >= new_len {
244            self.shrink(new_len);
245        } else {
246            while inner.header.size < new_len {
247                // Safety: The array must have a capacity of at least new_len because of the detach call earlier
248                unsafe {
249                    core::ptr::write(inner.data.as_mut_ptr().add(inner.header.size), value.clone());
250                }
251                inner.header.size += 1;
252            }
253        }
254    }
255
256    fn shrink(&mut self, new_len: usize) {
257        if self.len() == new_len {
258            return;
259        }
260
261        assert!(
262            unsafe { self.inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed) } == 1
263        );
264        // Safety: caller (and above debug_assert) must ensure that the array is not shared.
265        let inner = unsafe { self.inner.as_mut() };
266
267        while inner.header.size > new_len {
268            inner.header.size -= 1;
269            // Safety: The array was of size inner.header.size, so there should be an element there
270            unsafe {
271                core::ptr::drop_in_place(inner.data.as_mut_ptr().add(inner.header.size));
272            }
273        }
274    }
275
276    /// Clears the vector and removes all elements.
277    pub fn clear(&mut self) {
278        let is_shared =
279            unsafe { self.inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed) } != 1;
280        if is_shared {
281            *self = SharedVector::default();
282        } else {
283            self.shrink(0)
284        }
285    }
286}
287
288impl<T> Deref for SharedVector<T> {
289    type Target = [T];
290    fn deref(&self) -> &Self::Target {
291        self.as_slice()
292    }
293}
294
295/* FIXME: is this a good idea to implement DerefMut knowing what it might detach?
296impl<T> DerefMut for SharedVector<T> {
297    fn deref_mut(&mut self) -> &mut Self::Target {
298        self.as_mut_slice()
299    }
300}*/
301
302impl<T: Clone> From<&[T]> for SharedVector<T> {
303    fn from(slice: &[T]) -> Self {
304        let capacity = slice.len();
305        let mut result = Self::with_capacity(capacity);
306        for x in slice {
307            unsafe {
308                core::ptr::write(
309                    result.inner.as_mut().data.as_mut_ptr().add(result.inner.as_mut().header.size),
310                    x.clone(),
311                );
312                result.inner.as_mut().header.size += 1;
313            }
314        }
315        result
316    }
317}
318
319impl<T, const N: usize> From<[T; N]> for SharedVector<T> {
320    fn from(array: [T; N]) -> Self {
321        array.into_iter().collect()
322    }
323}
324
325impl<T> FromIterator<T> for SharedVector<T> {
326    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
327        let mut iter = iter.into_iter();
328        let mut capacity = iter.size_hint().0;
329        let mut result = Self::with_capacity(capacity);
330        let mut size = 0;
331        while let Some(x) = iter.next() {
332            if size >= capacity {
333                capacity = capacity_for_grow(
334                    capacity,
335                    size + 1 + iter.size_hint().0,
336                    core::mem::size_of::<T>(),
337                );
338                unsafe {
339                    result.inner.as_ref().header.refcount.store(0, atomic::Ordering::Relaxed)
340                };
341                let mut iter = IntoIter(IntoIterInner::UnShared(result.inner, 0));
342                result.inner = alloc_with_capacity::<T>(capacity);
343                match &mut iter.0 {
344                    IntoIterInner::UnShared(old_inner, begin) => {
345                        while *begin < size {
346                            unsafe {
347                                core::ptr::write(
348                                    result.inner.as_mut().data.as_mut_ptr().add(*begin),
349                                    core::ptr::read(old_inner.as_ref().data.as_ptr().add(*begin)),
350                                );
351                                *begin += 1;
352                                result.inner.as_mut().header.size = *begin;
353                            }
354                        }
355                    }
356                    _ => unreachable!(),
357                }
358            }
359            debug_assert_eq!(result.len(), size);
360            debug_assert!(result.capacity() > size);
361            unsafe {
362                core::ptr::write(result.inner.as_mut().data.as_mut_ptr().add(size), x);
363                size += 1;
364                result.inner.as_mut().header.size = size;
365            }
366        }
367        result
368    }
369}
370
371impl<T: Clone> Extend<T> for SharedVector<T> {
372    fn extend<X: IntoIterator<Item = T>>(&mut self, iter: X) {
373        let iter = iter.into_iter();
374        let hint = iter.size_hint().0;
375        if hint > 0 {
376            self.detach(capacity_for_grow(
377                self.capacity(),
378                self.len() + hint,
379                core::mem::size_of::<T>(),
380            ));
381        }
382        for item in iter {
383            self.push(item);
384        }
385    }
386}
387
388static SHARED_NULL: SharedVectorHeader =
389    SharedVectorHeader { refcount: atomic::AtomicIsize::new(-1), size: 0, capacity: 0 };
390
391impl<T> Default for SharedVector<T> {
392    fn default() -> Self {
393        SharedVector { inner: NonNull::from(&SHARED_NULL).cast() }
394    }
395}
396
397impl<T: Debug> Debug for SharedVector<T> {
398    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
399        self.as_slice().fmt(f)
400    }
401}
402
403impl<T> AsRef<[T]> for SharedVector<T> {
404    #[inline]
405    fn as_ref(&self) -> &[T] {
406        self.as_slice()
407    }
408}
409
410impl<T, U> PartialEq<U> for SharedVector<T>
411where
412    U: ?Sized + AsRef<[T]>,
413    T: PartialEq,
414{
415    fn eq(&self, other: &U) -> bool {
416        self.as_slice() == other.as_ref()
417    }
418}
419
420impl<T: Eq> Eq for SharedVector<T> {}
421
422impl<T: Clone> IntoIterator for SharedVector<T> {
423    type Item = T;
424    type IntoIter = IntoIter<T>;
425    fn into_iter(self) -> Self::IntoIter {
426        IntoIter(unsafe {
427            if self.inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed) == 1 {
428                let inner = self.inner;
429                core::mem::forget(self);
430                inner.as_ref().header.refcount.store(0, atomic::Ordering::Relaxed);
431                IntoIterInner::UnShared(inner, 0)
432            } else {
433                IntoIterInner::Shared(self, 0)
434            }
435        })
436    }
437}
438
439#[cfg(feature = "serde")]
440use serde::ser::SerializeSeq;
441#[cfg(feature = "serde")]
442impl<T> serde::Serialize for SharedVector<T>
443where
444    T: serde::Serialize,
445{
446    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
447    where
448        S: serde::Serializer,
449    {
450        let mut seq = serializer.serialize_seq(Some(self.len()))?;
451        for item in self.iter() {
452            seq.serialize_element(item)?;
453        }
454        seq.end()
455    }
456}
457
458#[cfg(feature = "serde")]
459impl<'de, T> serde::Deserialize<'de> for SharedVector<T>
460where
461    T: Clone + serde::Deserialize<'de>,
462{
463    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
464    where
465        D: serde::Deserializer<'de>,
466    {
467        let mut elements: alloc::vec::Vec<T> = serde::Deserialize::deserialize(deserializer)?;
468        let mut shared_vec = SharedVector::with_capacity(elements.len());
469        for elem in elements.drain(..) {
470            shared_vec.push(elem);
471        }
472        Ok(shared_vec)
473    }
474}
475
476enum IntoIterInner<T> {
477    Shared(SharedVector<T>, usize),
478    // Elements up to the usize member are already moved out
479    UnShared(NonNull<SharedVectorInner<T>>, usize),
480}
481
482impl<T> Drop for IntoIterInner<T> {
483    fn drop(&mut self) {
484        match self {
485            IntoIterInner::Shared(..) => { /* drop of SharedVector takes care of it */ }
486            IntoIterInner::UnShared(mut inner, begin) => unsafe {
487                debug_assert_eq!(inner.as_ref().header.refcount.load(atomic::Ordering::Relaxed), 0);
488                let data_ptr = inner.as_mut().data.as_mut_ptr();
489                for x in (*begin)..inner.as_ref().header.size {
490                    core::ptr::drop_in_place(data_ptr.add(x));
491                }
492                ::alloc::alloc::dealloc(
493                    inner.as_ptr() as *mut u8,
494                    compute_inner_layout::<T>(inner.as_ref().header.capacity),
495                )
496            },
497        }
498    }
499}
500
501/// An iterator that moves out of a SharedVector.
502///
503/// This `struct` is created by the `into_iter` method on [`SharedVector`] (provided
504/// by the [`IntoIterator`] trait).
505pub struct IntoIter<T>(IntoIterInner<T>);
506
507impl<T: Clone> Iterator for IntoIter<T> {
508    type Item = T;
509
510    fn next(&mut self) -> Option<Self::Item> {
511        match &mut self.0 {
512            IntoIterInner::Shared(array, moved) => {
513                let result = array.as_slice().get(*moved).cloned();
514                *moved += 1;
515                result
516            }
517            IntoIterInner::UnShared(inner, begin) => unsafe {
518                if *begin < inner.as_ref().header.size {
519                    let r = core::ptr::read(inner.as_ref().data.as_ptr().add(*begin));
520                    *begin += 1;
521                    Some(r)
522                } else {
523                    None
524                }
525            },
526        }
527    }
528}
529
530#[test]
531fn simple_test() {
532    let x: SharedVector<i32> = SharedVector::from([1, 2, 3]);
533    let y: SharedVector<i32> = SharedVector::from([3, 2, 1]);
534    assert_eq!(x, x.clone());
535    assert_ne!(x, y);
536    let z: [i32; 3] = [1, 2, 3];
537    assert_eq!(z, x.as_slice());
538    let vec: std::vec::Vec<i32> = std::vec![1, 2, 3];
539    assert_eq!(x, vec);
540    let def: SharedVector<i32> = Default::default();
541    assert_eq!(def, SharedVector::<i32>::default());
542    assert_ne!(def, x);
543}
544
545#[test]
546fn push_test() {
547    let mut x: SharedVector<i32> = SharedVector::from([1, 2, 3]);
548    let y = x.clone();
549    x.push(4);
550    x.push(5);
551    x.push(6);
552    assert_eq!(x.as_slice(), &[1, 2, 3, 4, 5, 6]);
553    assert_eq!(y.as_slice(), &[1, 2, 3]);
554}
555
556#[test]
557#[should_panic]
558fn invalid_capacity_test() {
559    let _: SharedVector<u8> = SharedVector::with_capacity(usize::MAX / 2 - 1000);
560}
561
562#[test]
563fn collect_from_iter_with_no_size_hint() {
564    use std::string::{String, ToString};
565    struct NoSizeHintIter<'a> {
566        data: &'a [&'a str],
567        i: usize,
568    }
569
570    impl Iterator for NoSizeHintIter<'_> {
571        type Item = String;
572
573        fn next(&mut self) -> Option<Self::Item> {
574            if self.i >= self.data.len() {
575                return None;
576            }
577            let item = self.data[self.i];
578            self.i += 1;
579            Some(item.to_string())
580        }
581
582        fn size_hint(&self) -> (usize, Option<usize>) {
583            (0, None)
584        }
585    }
586
587    // 5 elements to be above the initial "grow"-capacity of 4 and thus require one realloc.
588    let input = NoSizeHintIter { data: &["Hello", "sweet", "world", "of", "iterators"], i: 0 };
589
590    let shared_vec: SharedVector<String> = input.collect();
591    assert_eq!(shared_vec.as_slice(), &["Hello", "sweet", "world", "of", "iterators"]);
592}
593
594#[test]
595fn test_capacity_grows_only_when_needed() {
596    let mut vec: SharedVector<u8> = SharedVector::with_capacity(2);
597    vec.push(0);
598    assert_eq!(vec.capacity(), 2);
599    vec.push(0);
600    assert_eq!(vec.capacity(), 2);
601    vec.push(0);
602    assert_eq!(vec.len(), 3);
603    assert!(vec.capacity() > 2);
604}
605
606#[test]
607fn test_vector_clear() {
608    let mut vec: SharedVector<std::string::String> = Default::default();
609    vec.clear();
610    vec.push("Hello".into());
611    vec.push("World".into());
612    vec.push("of".into());
613    vec.push("Vectors".into());
614
615    let mut copy = vec.clone();
616
617    assert_eq!(vec.len(), 4);
618    let orig_cap = vec.capacity();
619    assert!(orig_cap >= vec.len());
620    vec.clear();
621    assert_eq!(vec.len(), 0);
622    assert_eq!(vec.capacity(), 0); // vec was shared, so start with new empty vector.
623    vec.push("Welcome back".into());
624    assert_eq!(vec.len(), 1);
625    assert!(vec.capacity() >= vec.len());
626
627    assert_eq!(copy.len(), 4);
628    assert_eq!(copy.capacity(), orig_cap);
629    copy.clear(); // copy is not shared (anymore), retain capacity.
630    assert_eq!(copy.capacity(), orig_cap);
631}
632
633#[test]
634fn pop_test() {
635    let mut x: SharedVector<i32> = SharedVector::from([1, 2, 3]);
636    let y = x.clone();
637    assert_eq!(x.pop(), Some(3));
638    assert_eq!(x.pop(), Some(2));
639    assert_eq!(x.pop(), Some(1));
640    assert_eq!(x.pop(), None);
641    assert!(x.is_empty());
642    assert_eq!(y.as_slice(), &[1, 2, 3]);
643}
644
645#[cfg(feature = "ffi")]
646pub(crate) mod ffi {
647    use super::*;
648
649    #[unsafe(no_mangle)]
650    /// This function is used for the low-level C++ interface to allocate the backing vector of a SharedVector.
651    pub unsafe extern "C" fn slint_shared_vector_allocate(size: usize, align: usize) -> *mut u8 {
652        alloc::alloc::alloc(alloc::alloc::Layout::from_size_align(size, align).unwrap())
653    }
654
655    #[unsafe(no_mangle)]
656    /// This function is used for the low-level C++ interface to deallocate the backing vector of a SharedVector
657    pub unsafe extern "C" fn slint_shared_vector_free(ptr: *mut u8, size: usize, align: usize) {
658        alloc::alloc::dealloc(ptr, alloc::alloc::Layout::from_size_align(size, align).unwrap())
659    }
660
661    #[unsafe(no_mangle)]
662    /// This function is used for the low-level C++ interface to initialize the empty SharedVector.
663    pub unsafe extern "C" fn slint_shared_vector_empty() -> *const u8 {
664        &SHARED_NULL as *const _ as *const u8
665    }
666}
667
668#[cfg(feature = "serde")]
669#[test]
670fn test_serialize_deserialize_sharedvector() {
671    let v = SharedVector::from([1, 2, 3]);
672    let serialized = serde_json::to_string(&v).unwrap();
673    let deserialized: SharedVector<i32> = serde_json::from_str(&serialized).unwrap();
674    assert_eq!(v, deserialized);
675}
i_slint_core/sharedvector.rs

i_slint_core/
sharedvector.rs
