Improved readability and reduced loops in pop

The `pop` was a bit more complicated than it needs to be.

src/lib.rs

@@ -17,19 +17,25 @@ use alloc::sync::Arc;
 #[cfg(not(loom))]
 use core::sync::atomic::{AtomicUsize, Ordering};
 
-const DATA_EMPTY: usize = 0;
-const DATA_AVAILABLE: usize = 1;
-const DATA_WRITING: usize = 2;
+const STATE_EMPTY: usize = 0;
+const STATE_AVAILABLE: usize = 1;
+const STATE_WRITING: usize = 2;
 // reading can be done by multiple readers
 // so we use value that is power of 2
 // we add this value to the state, which means there is a reader
-const DATA_READING: usize = 4;
-const READING_MASK: usize = usize::MAX & !(DATA_READING - 1);
+const STATE_READING: usize = 4;
+const READING_MASK: usize = usize::MAX & !(STATE_READING - 1);
 
-fn is_read_state(state: usize) -> bool {
+#[inline]
+fn is_reading(state: usize) -> bool {
     state & READING_MASK != 0
 }
 
+#[inline]
+fn is_readable(state: usize) -> bool {
+    state == STATE_AVAILABLE || is_reading(state)
+}
+
 struct Node<T> {
     data: UnsafeCell<MaybeUninit<T>>,
     state: AtomicUsize,
@@ -46,7 +52,7 @@ impl<T> Default for Node<T> {
     fn default() -> Self {
         Self {
             data: UnsafeCell::new(MaybeUninit::uninit()),
-            state: AtomicUsize::new(DATA_EMPTY),
+            state: AtomicUsize::new(STATE_EMPTY),
         }
     }
 }
@@ -113,29 +119,29 @@ impl<T: Clone, const N: usize> InnerChannel<T, N> {
         loop {
             let mut state = node.state.load(Ordering::Acquire);
 
-            while is_read_state(state) {
+            while is_reading(state) {
                 core::hint::spin_loop();
                 // wait until the reader is done
                 state = node.state.load(Ordering::Acquire);
             }
 
             match state {
-                DATA_EMPTY | DATA_AVAILABLE => {
+                STATE_EMPTY | STATE_AVAILABLE => {
                     if node
                         .state
                         .compare_exchange_weak(
                             state,
-                            DATA_WRITING,
+                            STATE_WRITING,
                             Ordering::Release,
                             Ordering::Relaxed,
                         )
                         .is_ok()
                     {
-                        should_drop = state == DATA_AVAILABLE;
+                        should_drop = state == STATE_AVAILABLE;
                         break;
                     }
                 }
-                DATA_WRITING => unreachable!("There should be no writer writing"),
+                STATE_WRITING => unreachable!("There should be no writer writing"),
                 s => unreachable!("Invalid state: {}", s),
             }
         }
@@ -153,7 +159,7 @@ impl<T: Clone, const N: usize> InnerChannel<T, N> {
         }
 
         // publish the value
-        node.state.store(DATA_AVAILABLE, Ordering::Release);
+        node.state.store(STATE_AVAILABLE, Ordering::Release);
     }
 
     fn pop(&self, reader: &mut ReaderData) -> Option<T> {
@@ -195,41 +201,23 @@ impl<T: Clone, const N: usize> InnerChannel<T, N> {
         loop {
             let state = node.state.load(Ordering::Acquire);
 
-            if is_read_state(state) {
-                let old = node.state.fetch_add(DATA_READING, Ordering::AcqRel);
+            if is_readable(state) {
+                let old = node.state.fetch_add(STATE_READING, Ordering::Release);
 
-                if old == state {
+                if is_readable(old) {
                     break;
-                } else {
-                    match old {
-                        DATA_AVAILABLE => {
-                            break;
-                        }
-                        _ => {
-                            // something happened, rollback
-                            // subtract one reader
-                            node.state.fetch_sub(DATA_READING, Ordering::AcqRel);
-                        }
-                    }
                 }
+                // something happened, rollback
+                node.state.fetch_sub(STATE_READING, Ordering::Release);
+                continue;
             }
 
             match state {
-                DATA_AVAILABLE => {
-                    let old = node.state.fetch_add(DATA_READING, Ordering::AcqRel);
-
-                    if old == state || is_read_state(old) {
-                        break;
-                    } else {
-                        // subtract one reader
-                        node.state.fetch_sub(DATA_READING, Ordering::AcqRel);
-                    }
-                }
-                DATA_WRITING => {
+                STATE_WRITING => {
                     reader_index += 1;
                     node = &self.buffer[reader_index % self.buffer.len()];
                 }
-                DATA_EMPTY => unreachable!("There should be some data at least"),
+                STATE_EMPTY => unreachable!("There should be some data at least"),
                 s => unreachable!("Invalid state: {}", s),
             }
         }
@@ -241,7 +229,7 @@ impl<T: Clone, const N: usize> InnerChannel<T, N> {
             reader.lap += 1;
         }
 
-        node.state.fetch_sub(DATA_READING, Ordering::Release);
+        node.state.fetch_sub(STATE_READING, Ordering::Release);
 
         Some(data)
     }