Remove PopError

This changes `pop` methods to return `Option`.
justanotherdot · Aug 30, 2020 · 69766ea · 69766ea
1 parent 35515d9
commit 69766ea
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Showing 7 changed files with 39 additions and 60 deletions.
diff --git a/crossbeam-channel/benchmarks/segqueue.rs b/crossbeam-channel/benchmarks/segqueue.rs
@@ -30,7 +30,7 @@ fn spsc() {
 
         for _ in 0..MESSAGES {
             loop {
-                if q.pop().is_err() {
+                if q.pop().is_none() {
                     thread::yield_now();
                 } else {
                     break;
@@ -55,7 +55,7 @@ fn mpsc() {
 
         for _ in 0..MESSAGES {
             loop {
-                if q.pop().is_err() {
+                if q.pop().is_none() {
                     thread::yield_now();
                 } else {
                     break;
@@ -82,7 +82,7 @@ fn mpmc() {
             scope.spawn(|_| {
                 for _ in 0..MESSAGES / THREADS {
                     loop {
-                        if q.pop().is_err() {
+                        if q.pop().is_none() {
                             thread::yield_now();
                         } else {
                             break;

diff --git a/crossbeam-queue/src/array_queue.rs b/crossbeam-queue/src/array_queue.rs
@@ -17,7 +17,7 @@ use core::sync::atomic::{self, AtomicUsize, Ordering};
 
 use crossbeam_utils::{Backoff, CachePadded};
 
-use crate::err::{PopError, PushError};
+use crate::err::PushError;
 
 /// A slot in a queue.
 struct Slot<T> {
@@ -50,7 +50,7 @@ struct Slot<T> {
 /// assert_eq!(q.push('a'), Ok(()));
 /// assert_eq!(q.push('b'), Ok(()));
 /// assert_eq!(q.push('c'), Err(PushError('c')));
-/// assert_eq!(q.pop(), Ok('a'));
+/// assert_eq!(q.pop(), Some('a'));
 /// ```
 pub struct ArrayQueue<T> {
     /// The head of the queue.
@@ -218,20 +218,20 @@ impl<T> ArrayQueue<T> {
 
     /// Attempts to pop an element from the queue.
     ///
-    /// If the queue is empty, an error is returned.
+    /// If the queue is empty, `None` is returned.
     ///
     /// # Examples
     ///
     /// ```
-    /// use crossbeam_queue::{ArrayQueue, PopError};
+    /// use crossbeam_queue::ArrayQueue;
     ///
     /// let q = ArrayQueue::new(1);
     /// assert_eq!(q.push(10), Ok(()));
     ///
-    /// assert_eq!(q.pop(), Ok(10));
-    /// assert_eq!(q.pop(), Err(PopError));
+    /// assert_eq!(q.pop(), Some(10));
+    /// assert!(q.pop().is_none());
     /// ```
-    pub fn pop(&self) -> Result<T, PopError> {
+    pub fn pop(&self) -> Option<T> {
         let backoff = Backoff::new();
         let mut head = self.head.load(Ordering::Relaxed);
 
@@ -268,7 +268,7 @@ impl<T> ArrayQueue<T> {
                         let msg = unsafe { slot.value.get().read().assume_init() };
                         slot.stamp
                             .store(head.wrapping_add(self.one_lap), Ordering::Release);
-                        return Ok(msg);
+                        return Some(msg);
                     }
                     Err(h) => {
                         head = h;
@@ -281,7 +281,7 @@ impl<T> ArrayQueue<T> {
 
                 // If the tail equals the head, that means the channel is empty.
                 if tail == head {
-                    return Err(PopError);
+                    return None;
                 }
 
                 backoff.spin();

diff --git a/crossbeam-queue/src/err.rs b/crossbeam-queue/src/err.rs
@@ -1,24 +1,5 @@
 use core::fmt;
 
-/// Error which occurs when popping from an empty queue.
-#[derive(Clone, Copy, Eq, PartialEq)]
-pub struct PopError;
-
-impl fmt::Debug for PopError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        "PopError".fmt(f)
-    }
-}
-
-impl fmt::Display for PopError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        "popping from an empty queue".fmt(f)
-    }
-}
-
-#[cfg(feature = "std")]
-impl ::std::error::Error for PopError {}
-
 /// Error which occurs when pushing into a full queue.
 #[derive(Clone, Copy, Eq, PartialEq)]
 pub struct PushError<T>(pub T);

diff --git a/crossbeam-queue/src/lib.rs b/crossbeam-queue/src/lib.rs
@@ -29,7 +29,7 @@ cfg_if::cfg_if! {
         mod seg_queue;
 
         pub use self::array_queue::ArrayQueue;
-        pub use self::err::{PopError, PushError};
+        pub use self::err::PushError;
         pub use self::seg_queue::SegQueue;
     }
 }
diff --git a/crossbeam-queue/src/seg_queue.rs b/crossbeam-queue/src/seg_queue.rs
@@ -8,8 +8,6 @@ use core::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
 
 use crossbeam_utils::{Backoff, CachePadded};
 
-use crate::err::PopError;
-
 // Bits indicating the state of a slot:
 // * If a value has been written into the slot, `WRITE` is set.
 // * If a value has been read from the slot, `READ` is set.
@@ -123,16 +121,16 @@ struct Position<T> {
 /// # Examples
 ///
 /// ```
-/// use crossbeam_queue::{PopError, SegQueue};
+/// use crossbeam_queue::SegQueue;
 ///
 /// let q = SegQueue::new();
 ///
 /// q.push('a');
 /// q.push('b');
 ///
-/// assert_eq!(q.pop(), Ok('a'));
-/// assert_eq!(q.pop(), Ok('b'));
-/// assert_eq!(q.pop(), Err(PopError));
+/// assert_eq!(q.pop(), Some('a'));
+/// assert_eq!(q.pop(), Some('b'));
+/// assert!(q.pop().is_none());
 /// ```
 pub struct SegQueue<T> {
     /// The head of the queue.
@@ -266,20 +264,20 @@ impl<T> SegQueue<T> {
 
     /// Pops an element from the queue.
     ///
-    /// If the queue is empty, an error is returned.
+    /// If the queue is empty, `None` is returned.
     ///
     /// # Examples
     ///
     /// ```
-    /// use crossbeam_queue::{PopError, SegQueue};
+    /// use crossbeam_queue::SegQueue;
     ///
     /// let q = SegQueue::new();
     ///
     /// q.push(10);
-    /// assert_eq!(q.pop(), Ok(10));
-    /// assert_eq!(q.pop(), Err(PopError));
+    /// assert_eq!(q.pop(), Some(10));
+    /// assert!(q.pop().is_none());
     /// ```
-    pub fn pop(&self) -> Result<T, PopError> {
+    pub fn pop(&self) -> Option<T> {
         let backoff = Backoff::new();
         let mut head = self.head.index.load(Ordering::Acquire);
         let mut block = self.head.block.load(Ordering::Acquire);
@@ -304,7 +302,7 @@ impl<T> SegQueue<T> {
 
                 // If the tail equals the head, that means the queue is empty.
                 if head >> SHIFT == tail >> SHIFT {
-                    return Err(PopError);
+                    return None;
                 }
 
                 // If head and tail are not in the same block, set `HAS_NEXT` in head.
@@ -355,7 +353,7 @@ impl<T> SegQueue<T> {
                         Block::destroy(block, offset + 1);
                     }
 
-                    return Ok(value);
+                    return Some(value);
                 },
                 Err(h) => {
                     head = h;

diff --git a/crossbeam-queue/tests/array_queue.rs b/crossbeam-queue/tests/array_queue.rs
@@ -9,11 +9,11 @@ fn smoke() {
     let q = ArrayQueue::new(1);
 
     q.push(7).unwrap();
-    assert_eq!(q.pop(), Ok(7));
+    assert_eq!(q.pop(), Some(7));
 
     q.push(8).unwrap();
-    assert_eq!(q.pop(), Ok(8));
-    assert!(q.pop().is_err());
+    assert_eq!(q.pop(), Some(8));
+    assert!(q.pop().is_none());
 }
 
 #[test]
@@ -92,7 +92,7 @@ fn len() {
         scope.spawn(|_| {
             for i in 0..COUNT {
                 loop {
-                    if let Ok(x) = q.pop() {
+                    if let Some(x) = q.pop() {
                         assert_eq!(x, i);
                         break;
                     }
@@ -124,13 +124,13 @@ fn spsc() {
         scope.spawn(|_| {
             for i in 0..COUNT {
                 loop {
-                    if let Ok(x) = q.pop() {
+                    if let Some(x) = q.pop() {
                         assert_eq!(x, i);
                         break;
                     }
                 }
             }
-            assert!(q.pop().is_err());
+            assert!(q.pop().is_none());
         });
 
         scope.spawn(|_| {
@@ -155,7 +155,7 @@ fn mpmc() {
             scope.spawn(|_| {
                 for _ in 0..COUNT {
                     let n = loop {
-                        if let Ok(x) = q.pop() {
+                        if let Some(x) = q.pop() {
                             break x;
                         }
                     };
@@ -205,7 +205,7 @@ fn drops() {
         scope(|scope| {
             scope.spawn(|_| {
                 for _ in 0..steps {
-                    while q.pop().is_err() {}
+                    while q.pop().is_none() {}
                 }
             });
 

diff --git a/crossbeam-queue/tests/seg_queue.rs b/crossbeam-queue/tests/seg_queue.rs
@@ -8,11 +8,11 @@ use rand::{thread_rng, Rng};
 fn smoke() {
     let q = SegQueue::new();
     q.push(7);
-    assert_eq!(q.pop(), Ok(7));
+    assert_eq!(q.pop(), Some(7));
 
     q.push(8);
-    assert_eq!(q.pop(), Ok(8));
-    assert!(q.pop().is_err());
+    assert_eq!(q.pop(), Some(8));
+    assert!(q.pop().is_none());
 }
 
 #[test]
@@ -62,13 +62,13 @@ fn spsc() {
         scope.spawn(|_| {
             for i in 0..COUNT {
                 loop {
-                    if let Ok(x) = q.pop() {
+                    if let Some(x) = q.pop() {
                         assert_eq!(x, i);
                         break;
                     }
                 }
             }
-            assert!(q.pop().is_err());
+            assert!(q.pop().is_none());
         });
         scope.spawn(|_| {
             for i in 0..COUNT {
@@ -92,7 +92,7 @@ fn mpmc() {
             scope.spawn(|_| {
                 for _ in 0..COUNT {
                     let n = loop {
-                        if let Ok(x) = q.pop() {
+                        if let Some(x) = q.pop() {
                             break x;
                         }
                     };
@@ -140,7 +140,7 @@ fn drops() {
         scope(|scope| {
             scope.spawn(|_| {
                 for _ in 0..steps {
-                    while q.pop().is_err() {}
+                    while q.pop().is_none() {}
                 }
             });