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1 | //! Reference-counted buffer data type. | |
2 | //! | |
3 | //! NihAV requires some reference-counted type especially for frame buffer pools. | |
4 | //! `Arc` does not allow mutability with several references present, `RwLock` does not work reliably in a single thread mode (at least for me) so I ended up NIHing something. | |
5 | //! | |
6 | //! Currently it does not prevent code from reading the data that is being written to. | |
7 | //! Maybe in the future this will be replaced by something better and using more standard components. | |
8 | //! | |
9 | //! Also it contains `unsafe{}` so I should not write in Rust at all. | |
10 | //! | |
11 | //! # Examples | |
12 | //! | |
13 | //! ``` | |
14 | //! use nihav_core::refs::NABufferRef; | |
15 | //! | |
16 | //! let vec = vec![42u8; 16]; | |
17 | //! let vec_ref = NABufferRef::new(vec); | |
18 | //! let vec_ref2 = vec_ref.clone(); | |
19 | //! let ref_count = vec_ref.get_num_refs(); // should be 2 | |
20 | //! println!("vector element 4 is {}", vec_ref[4]); // should print the fourth vector element | |
21 | //! ``` | |
22 | use std::ops::{Deref, DerefMut}; | |
23 | use std::convert::AsRef; | |
24 | use std::sync::atomic::*; | |
25 | ||
26 | struct NABufferData<T> { | |
27 | data: T, | |
28 | refs: AtomicUsize, | |
29 | } | |
30 | ||
31 | impl<T> NABufferData<T> { | |
32 | fn new(data: T) -> Self { | |
33 | Self { | |
34 | data, | |
35 | refs: AtomicUsize::new(1), | |
36 | } | |
37 | } | |
38 | fn inc_refs(obj: &mut Self) { | |
39 | obj.refs.fetch_add(1, Ordering::SeqCst); | |
40 | } | |
41 | fn dec_refs(obj: &mut Self) -> bool { | |
42 | obj.refs.fetch_sub(1, Ordering::SeqCst) == 1 | |
43 | } | |
44 | fn get_num_refs(obj: &Self) -> usize { | |
45 | obj.refs.load(Ordering::Relaxed) | |
46 | } | |
47 | fn get_read_ptr(obj: &Self) -> &T { | |
48 | &obj.data | |
49 | } | |
50 | fn get_write_ptr(obj: &mut Self) -> Option<&mut T> { | |
51 | Some(&mut obj.data) | |
52 | } | |
53 | } | |
54 | ||
55 | /// Reference-counted buffer reference. | |
56 | pub struct NABufferRef<T> { | |
57 | ptr: *mut NABufferData<T>, | |
58 | } | |
59 | ||
60 | unsafe impl<T> Sync for NABufferRef<T> {} | |
61 | unsafe impl<T> Send for NABufferRef<T> {} | |
62 | ||
63 | impl<T> NABufferRef<T> { | |
64 | /// Constructs a new instance of `NABufferRef`. | |
65 | pub fn new(val: T) -> Self { | |
66 | let bdata = NABufferData::new(val); | |
67 | let nbox: Box<_> = Box::new(bdata); | |
68 | Self { ptr: Box::into_raw(nbox) } | |
69 | } | |
70 | /// Reports the number of references for the current instance. | |
71 | pub fn get_num_refs(&self) -> usize { | |
72 | unsafe { | |
73 | NABufferData::get_num_refs(self.ptr.as_mut().unwrap()) | |
74 | } | |
75 | } | |
76 | /// Returns a mutable pointer to the underlying data if possible. | |
77 | pub fn as_mut(&mut self) -> Option<&mut T> { | |
78 | unsafe { | |
79 | NABufferData::get_write_ptr(self.ptr.as_mut().unwrap()) | |
80 | } | |
81 | } | |
82 | } | |
83 | ||
84 | impl<T> AsRef<T> for NABufferRef<T> { | |
85 | fn as_ref(&self) -> &T { | |
86 | unsafe { | |
87 | NABufferData::get_read_ptr(self.ptr.as_mut().unwrap()) | |
88 | } | |
89 | } | |
90 | } | |
91 | ||
92 | impl<T> Deref for NABufferRef<T> { | |
93 | type Target = T; | |
94 | fn deref(&self) -> &T { self.as_ref() } | |
95 | } | |
96 | ||
97 | impl<T> DerefMut for NABufferRef<T> { | |
98 | fn deref_mut(&mut self) -> &mut T { self.as_mut().unwrap() } | |
99 | } | |
100 | ||
101 | impl<T> Clone for NABufferRef<T> { | |
102 | fn clone(&self) -> Self { | |
103 | unsafe { | |
104 | NABufferData::inc_refs(self.ptr.as_mut().unwrap()); | |
105 | } | |
106 | Self { ptr: self.ptr } | |
107 | } | |
108 | } | |
109 | ||
110 | impl<T> Drop for NABufferRef<T> { | |
111 | fn drop(&mut self) { | |
112 | unsafe { | |
113 | if NABufferData::dec_refs(self.ptr.as_mut().unwrap()) { | |
114 | let data = Box::from_raw(self.ptr); | |
115 | std::mem::drop(data); | |
116 | } | |
117 | } | |
118 | } | |
119 | } | |
120 | ||
121 | impl<T:Default> Default for NABufferRef<T> { | |
122 | fn default() -> Self { | |
123 | Self::new(T::default()) | |
124 | } | |
125 | } |