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//! Simple MPMC Queue for VelocityX
//!
//! A basic multi-producer, multi-consumer queue implementation.
use crate::metrics::{AtomicMetrics, MetricsCollector};
use crate::util::CachePadded;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use std::vec::Vec;
#[cfg(feature = "std")]
use std::time::Duration;
/// A simple bounded MPMC queue
#[derive(Debug)]
pub struct MpmcQueue<T> {
buffer: Arc<Mutex<Vec<Option<T>>>>,
capacity: usize,
head: CachePadded<AtomicUsize>,
tail: CachePadded<AtomicUsize>,
push_lock: Mutex<()>,
pop_lock: Mutex<()>,
metrics: AtomicMetrics,
metrics_enabled: AtomicUsize,
}
impl<T> MpmcQueue<T> {
/// Create a new MPMC queue with the specified capacity
pub fn new(capacity: usize) -> Self {
assert!(capacity > 0, "Capacity must be greater than 0");
Self {
buffer: Arc::new(Mutex::new((0..capacity).map(|_| None).collect())),
capacity,
head: CachePadded::new(AtomicUsize::new(0)),
tail: CachePadded::new(AtomicUsize::new(0)),
push_lock: Mutex::new(()),
pop_lock: Mutex::new(()),
metrics: AtomicMetrics::default(),
metrics_enabled: AtomicUsize::new(1), // Enabled by default
}
}
/// Push a value into the queue
pub fn push(&self, value: T) -> Result<(), crate::Error> {
#[cfg(feature = "std")]
let start = std::time::Instant::now();
let _guard = self.push_lock.lock().unwrap();
let tail = self.tail.get().load(Ordering::Relaxed);
let head = self.head.get().load(Ordering::Relaxed);
if tail - head >= self.capacity {
#[cfg(feature = "std")]
self.metrics.record_failure();
return Err(crate::Error::WouldBlock);
}
let index = tail % self.capacity;
{
let mut buffer = self.buffer.lock().unwrap();
buffer[index] = Some(value);
}
self.tail.get().store(tail + 1, Ordering::Release);
#[cfg(feature = "std")]
self.metrics.record_success(start.elapsed());
Ok(())
}
/// Pop a value from the queue
pub fn pop(&self) -> Option<T> {
#[cfg(feature = "std")]
let start = std::time::Instant::now();
let _guard = self.pop_lock.lock().unwrap();
let head = self.head.get().load(Ordering::Relaxed);
let tail = self.tail.get().load(Ordering::Relaxed);
if head == tail {
#[cfg(feature = "std")]
self.metrics.record_failure();
return None;
}
let index = head % self.capacity;
let value = {
let mut buffer = self.buffer.lock().unwrap();
buffer[index].take()
};
self.head.get().store(head + 1, Ordering::Release);
#[cfg(feature = "std")]
self.metrics.record_success(start.elapsed());
value
}
/// Try to push without blocking
pub fn try_push(&self, value: T) -> Result<(), crate::Error> {
self.push(value)
}
/// Try to pop without blocking
pub fn try_pop(&self) -> Option<T> {
self.pop()
}
/// Get the current number of elements in the queue
pub fn len(&self) -> usize {
let head = self.head.get().load(Ordering::Relaxed);
let tail = self.tail.get().load(Ordering::Relaxed);
tail - head
}
/// Check if the queue is empty
pub fn is_empty(&self) -> bool {
let head = self.head.get().load(Ordering::Relaxed);
let tail = self.tail.get().load(Ordering::Relaxed);
head == tail
}
/// Get the capacity of the queue
pub fn capacity(&self) -> usize {
self.capacity
}
/// Push multiple elements to the queue in a single operation
///
/// This is more efficient than individual pushes as it reduces lock contention.
/// Returns the number of elements successfully pushed.
///
/// # Arguments
///
/// * `values` - Iterator of values to push
///
/// # Returns
///
/// Number of elements successfully pushed
///
/// # Examples
///
/// ```rust
/// use velocityx::queue::MpmcQueue;
///
/// let queue: MpmcQueue<i32> = MpmcQueue::new(10);
/// let values = vec![1, 2, 3, 4, 5];
/// let pushed = queue.push_batch(values);
/// assert_eq!(pushed, 5);
/// ```
pub fn push_batch<I>(&self, values: I) -> usize
where
I: IntoIterator<Item = T>,
{
let _guard = self.push_lock.lock().unwrap();
let mut pushed = 0;
let tail = self.tail.get().load(Ordering::Relaxed);
let head = self.head.get().load(Ordering::Relaxed);
let available_space = self.capacity - (tail - head);
for value in values.into_iter().take(available_space) {
let index = (tail + pushed) % self.capacity;
{
let mut buffer = self.buffer.lock().unwrap();
buffer[index] = Some(value);
}
pushed += 1;
}
self.tail.get().store(tail + pushed, Ordering::Release);
pushed
}
/// Pop multiple elements from the queue in a single operation
///
/// This is more efficient than individual pops as it reduces lock contention.
///
/// # Arguments
///
/// * `max_values` - Maximum number of values to pop
///
/// # Returns
///
/// Vector of popped values (may be empty if queue is empty)
///
/// # Examples
///
/// ```rust
/// use velocityx::queue::MpmcQueue;
///
/// let queue: MpmcQueue<i32> = MpmcQueue::new(10);
/// queue.push(1).unwrap();
/// queue.push(2).unwrap();
/// queue.push(3).unwrap();
///
/// let values = queue.pop_batch(2);
/// assert_eq!(values.len(), 2);
/// ```
pub fn pop_batch(&self, max_values: usize) -> Vec<T> {
let _guard = self.pop_lock.lock().unwrap();
let head = self.head.get().load(Ordering::Relaxed);
let tail = self.tail.get().load(Ordering::Relaxed);
let available_items = tail - head;
let items_to_pop = std::cmp::min(max_values, available_items);
let mut values = Vec::with_capacity(items_to_pop);
for i in 0..items_to_pop {
let index = (head + i) % self.capacity;
{
let mut buffer = self.buffer.lock().unwrap();
if let Some(value) = buffer[index].take() {
values.push(value);
}
}
}
self.head
.get()
.store(head + items_to_pop, Ordering::Release);
values
}
/// Try to push an element with a timeout
///
/// This operation will retry for the specified duration before giving up.
/// Uses adaptive backoff to reduce contention.
///
/// # Arguments
///
/// * `timeout` - Duration to wait before giving up
/// * `value_factory` - Closure that produces the value to push (called only when needed)
///
/// # Returns
///
/// * `Ok(())` if the element was successfully pushed
/// * `Err(crate::Error::Timeout)` if the timeout expired
///
/// # Examples
///
/// ```rust
/// use velocityx::queue::MpmcQueue;
/// use std::time::Duration;
///
/// let queue: MpmcQueue<i32> = MpmcQueue::new(1);
/// queue.push(42).unwrap();
///
/// let result = queue.push_with_timeout(Duration::from_millis(100), || 43);
/// assert!(result.is_err()); // Queue full, timeout
/// ```
#[cfg(feature = "std")]
pub fn push_with_timeout<F>(
&self,
timeout: Duration,
mut value_factory: F,
) -> Result<(), crate::Error>
where
F: FnMut() -> T,
{
let start = std::time::Instant::now();
let mut backoff = Duration::from_nanos(100);
while start.elapsed() < timeout {
match self.push(value_factory()) {
Ok(()) => return Ok(()),
Err(crate::Error::WouldBlock) => {
// Adaptive backoff with exponential growth
let elapsed = start.elapsed();
let remaining = timeout - elapsed;
if backoff > remaining {
break;
}
std::thread::sleep(backoff);
backoff = std::cmp::min(backoff * 2, Duration::from_millis(1));
}
Err(e) => return Err(e),
}
}
Err(crate::Error::Timeout)
}
/// Try to pop an element with a timeout
///
/// This operation will retry for the specified duration before giving up.
/// Uses adaptive backoff to reduce contention.
///
/// # Arguments
///
/// * `timeout` - Duration to wait before giving up
///
/// # Returns
///
/// * `Some(value)` if an element was successfully popped
/// * `None` if the timeout expired
///
/// # Examples
///
/// ```rust
/// use velocityx::queue::MpmcQueue;
/// use std::time::Duration;
///
/// let queue: MpmcQueue<i32> = MpmcQueue::new(10);
///
/// let result = queue.pop_with_timeout(Duration::from_millis(100));
/// assert!(result.is_none()); // Queue empty, timeout
/// ```
#[cfg(feature = "std")]
pub fn pop_with_timeout(&self, timeout: Duration) -> Option<T> {
let start = std::time::Instant::now();
let mut backoff = Duration::from_nanos(50);
while start.elapsed() < timeout {
if let Some(value) = self.pop() {
return Some(value);
}
// Adaptive backoff with exponential growth
let elapsed = start.elapsed();
let remaining = timeout - elapsed;
if backoff > remaining {
break;
}
std::thread::sleep(backoff);
backoff = std::cmp::min(backoff * 2, Duration::from_millis(1));
}
None
}
}
/// Performance metrics for MPMC queue
#[derive(Debug, Clone)]
pub struct QueueMetrics {
/// Maximum capacity of the queue
pub capacity: usize,
/// Current number of elements
pub current_len: usize,
/// Whether the queue is empty
pub is_empty: bool,
/// Utilization ratio (0.0 to 1.0)
pub utilization_ratio: f64,
}
impl<T> Clone for MpmcQueue<T> {
fn clone(&self) -> Self {
Self {
buffer: Arc::clone(&self.buffer),
capacity: self.capacity,
head: CachePadded::new(AtomicUsize::new(self.head.get().load(Ordering::Relaxed))),
tail: CachePadded::new(AtomicUsize::new(self.tail.get().load(Ordering::Relaxed))),
push_lock: Mutex::new(()),
pop_lock: Mutex::new(()),
metrics: AtomicMetrics::default(),
metrics_enabled: AtomicUsize::new(self.metrics_enabled.load(Ordering::Relaxed)),
}
}
}
impl<T> Drop for MpmcQueue<T> {
fn drop(&mut self) {
// Clear all remaining elements
if let Ok(mut buffer) = self.buffer.lock() {
for item in buffer.iter_mut() {
*item = None;
}
}
}
}
#[cfg(feature = "std")]
impl<T> MetricsCollector for MpmcQueue<T> {
fn metrics(&self) -> crate::metrics::PerformanceMetrics {
self.metrics.snapshot()
}
fn reset_metrics(&self) {
self.metrics.reset();
}
fn set_metrics_enabled(&self, enabled: bool) {
self.metrics_enabled
.store(enabled as usize, std::sync::atomic::Ordering::Relaxed);
}
fn is_metrics_enabled(&self) -> bool {
self.metrics_enabled
.load(std::sync::atomic::Ordering::Relaxed)
!= 0
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_basic_operations() {
let queue: MpmcQueue<i32> = MpmcQueue::new(3);
assert!(queue.is_empty());
assert_eq!(queue.len(), 0);
assert_eq!(queue.pop(), None);
queue.push(1).unwrap();
queue.push(2).unwrap();
queue.push(3).unwrap();
assert_eq!(queue.len(), 3);
assert!(!queue.is_empty());
assert_eq!(queue.push(4), Err(crate::Error::WouldBlock));
assert_eq!(queue.pop(), Some(1));
assert_eq!(queue.pop(), Some(2));
assert_eq!(queue.pop(), Some(3));
assert_eq!(queue.pop(), None);
assert!(queue.is_empty());
assert_eq!(queue.len(), 0);
}
}