nihav-core/src/refs.rs

   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 }