Reuse allocation for pending_removal in poll(2) impl

src/sys/unix/selector/poll.rs

@@ -5,6 +5,7 @@
 
 use std::collections::HashMap;
 use std::fmt::{Debug, Formatter};
+use std::mem::swap;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::sync::{Arc, Condvar, Mutex};
@@ -26,7 +27,8 @@ pub struct Selector {
  #[cfg(debug_assertions)]
  has_waker: AtomicBool,
  /// Buffer used in [`SelectorState::select`].
- fd_bufs: Vec<RawFd>,
+ fd_bufs0: Vec<RawFd>,
+ fd_bufs1: Vec<RawFd>,
 }
 
 impl Selector {
@@ -35,7 +37,8 @@ impl Selector {
  state: Arc::new(SelectorState::new()?),
  #[cfg(debug_assertions)]
  has_waker: AtomicBool::new(false),
- fd_bufs: Vec::new(),
+ fd_bufs0: Vec::new(),
+ fd_bufs1: Vec::new(),
  })
  }
 
@@ -45,12 +48,14 @@ impl Selector {
  state: self.state.clone(),
  #[cfg(debug_assertions)]
  has_waker: AtomicBool::new(self.has_waker.load(Ordering::Acquire)),
- fd_bufs: Vec::new(),
+ fd_bufs0: Vec::new(),
+ fd_bufs1: Vec::new(),
  })
  }
 
  pub fn select(&mut self, events: &mut Events, timeout: Option<Duration>) -> io::Result<()> {
- self.state.select(events, timeout, &mut self.fd_bufs)
+ self.state
+ .select(events, timeout, &mut self.fd_bufs0, &mut self.fd_bufs1)
  }
 
  pub fn register(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
@@ -195,9 +200,11 @@ impl SelectorState {
  events: &mut Events,
  timeout: Option<Duration>,
  closed_raw_fds: &mut Vec<RawFd>,
+ pending_removal: &mut Vec<RawFd>,
  ) -> io::Result<()> {
  events.clear();
  closed_raw_fds.clear();
+ pending_removal.clear();
 
  let mut fds = self.fds.lock().unwrap();
 
@@ -236,7 +243,7 @@ impl SelectorState {
  // We now check whether this poll was performed with descriptors which were pending
  // for removal and filter out any matching.
  let mut pending_removal_guard = self.pending_removal.lock().unwrap();
- let mut pending_removal = std::mem::replace(pending_removal_guard.as_mut(), Vec::new());
+ swap(pending_removal_guard.as_mut(), pending_removal);
  drop(pending_removal_guard);
 
  // Store the events if there were any.