core/scale: fix check for checking formats subsampling differences

[nihav.git] / nihav-core / src / refs.rs

diff --git a/nihav-core/src/refs.rs b/nihav-core/src/refs.rs
index f2b0577866174e1d5910f6062e1b4e9ef23aceaa..e4cde3a369f7c114c7d7d1daffb8de81f7bd8c7f 100644 (file)
--- a/nihav-core/src/refs.rs
+++ b/nihav-core/src/refs.rs
@@ -1,4 +1,26 @@
+//! Reference-counted buffer data type.
+//!
+//! NihAV requires some reference-counted type especially for frame buffer pools.
+//! `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.
+//!
+//! Currently it does not prevent code from reading the data that is being written to.
+//! Maybe in the future this will be replaced by something better and using more standard components.
+//!
+//! Also it contains `unsafe{}` so I should not write in Rust at all.
+//!
+//! # Examples
+//!
+//! ```
+//! use nihav_core::refs::NABufferRef;
+//!
+//! let vec = vec![42u8; 16];
+//! let vec_ref = NABufferRef::new(vec);
+//! let vec_ref2 = vec_ref.clone();
+//! let ref_count = vec_ref.get_num_refs(); // should be 2
+//! println!("vector element 4 is {}", vec_ref[4]); // should print the fourth vector element
+//! ```
 use std::ops::{Deref, DerefMut};
+use std::convert::AsRef;
 use std::sync::atomic::*;
 
 struct NABufferData<T> {
@@ -9,17 +31,15 @@ struct NABufferData<T> {
 impl<T> NABufferData<T> {
     fn new(data: T) -> Self {
         Self {
-            data:       data,
+            data,
             refs:       AtomicUsize::new(1),
         }
     }
     fn inc_refs(obj: &mut Self) {
         obj.refs.fetch_add(1, Ordering::SeqCst);
     }
-    fn dec_refs(obj: &mut Self) {
-        if obj.refs.fetch_sub(1, Ordering::SeqCst) == 0 {
-            std::mem::forget(obj);
-        }
+    fn dec_refs(obj: &mut Self) -> bool {
+        obj.refs.fetch_sub(1, Ordering::SeqCst) == 1
     }
     fn get_num_refs(obj: &Self) -> usize {
         obj.refs.load(Ordering::Relaxed)
@@ -32,29 +52,39 @@ impl<T> NABufferData<T> {
     }
 }
 
+/// Reference-counted buffer reference.
 pub struct NABufferRef<T> {
     ptr: *mut NABufferData<T>,
 }
 
+unsafe impl<T> Sync for NABufferRef<T> {}
+unsafe impl<T> Send for NABufferRef<T> {}
+
 impl<T> NABufferRef<T> {
+    /// Constructs a new instance of `NABufferRef`.
     pub fn new(val: T) -> Self {
         let bdata = NABufferData::new(val);
         let nbox: Box<_> = Box::new(bdata);
         Self { ptr: Box::into_raw(nbox) }
     }
+    /// Reports the number of references for the current instance.
     pub fn get_num_refs(&self) -> usize {
         unsafe {
             NABufferData::get_num_refs(self.ptr.as_mut().unwrap())
         }
     }
-    pub fn as_ref(&self) -> &T {
+    /// Returns a mutable pointer to the underlying data if possible.
+    pub fn as_mut(&mut self) -> Option<&mut T> {
         unsafe {
-            NABufferData::get_read_ptr(self.ptr.as_mut().unwrap())
+            NABufferData::get_write_ptr(self.ptr.as_mut().unwrap())
         }
     }
-    pub fn as_mut(&mut self) -> Option<&mut T> {
+}
+
+impl<T> AsRef<T> for NABufferRef<T> {
+    fn as_ref(&self) -> &T {
         unsafe {
-            NABufferData::get_write_ptr(self.ptr.as_mut().unwrap())
+            NABufferData::get_read_ptr(self.ptr.as_mut().unwrap())
         }
     }
 }
@@ -80,8 +110,16 @@ impl<T> Clone for NABufferRef<T> {
 impl<T> Drop for NABufferRef<T> {
     fn drop(&mut self) {
         unsafe {
-            NABufferData::dec_refs(self.ptr.as_mut().unwrap());
+            if NABufferData::dec_refs(self.ptr.as_mut().unwrap()) {
+                let data = Box::from_raw(self.ptr);
+                std::mem::drop(data);
+            }
         }
     }
 }
 
+impl<T:Default> Default for NABufferRef<T> {
+    fn default() -> Self {
+        Self::new(T::default())
+    }
+}