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use crate::timer::timer::Entry;
use crate::timer::wheel;
use std::ptr;
use std::sync::Arc;
/// A doubly linked stack
#[derive(Debug)]
pub(crate) struct Stack {
head: Option<Arc<Entry>>,
}
impl Default for Stack {
fn default() -> Stack {
Stack { head: None }
}
}
impl wheel::Stack for Stack {
type Owned = Arc<Entry>;
type Borrowed = Entry;
type Store = ();
fn is_empty(&self) -> bool {
self.head.is_none()
}
fn push(&mut self, entry: Self::Owned, _: &mut Self::Store) {
// Get a pointer to the entry to for the prev link
let ptr: *const Entry = &*entry as *const _;
// Remove the old head entry
let old = self.head.take();
unsafe {
// Ensure the entry is not already in a stack.
debug_assert!((*entry.next_stack.get()).is_none());
debug_assert!((*entry.prev_stack.get()).is_null());
if let Some(ref entry) = old.as_ref() {
debug_assert!({
// The head is not already set to the entry
ptr != &***entry as *const _
});
// Set the previous link on the old head
*entry.prev_stack.get() = ptr;
}
// Set this entry's next pointer
*entry.next_stack.get() = old;
}
// Update the head pointer
self.head = Some(entry);
}
/// Pop an item from the stack
fn pop(&mut self, _: &mut ()) -> Option<Arc<Entry>> {
let entry = self.head.take();
unsafe {
if let Some(entry) = entry.as_ref() {
self.head = (*entry.next_stack.get()).take();
if let Some(entry) = self.head.as_ref() {
*entry.prev_stack.get() = ptr::null();
}
*entry.prev_stack.get() = ptr::null();
}
}
entry
}
fn remove(&mut self, entry: &Entry, _: &mut ()) {
unsafe {
// Ensure that the entry is in fact contained by the stack
debug_assert!({
// This walks the full linked list even if an entry is found.
let mut next = self.head.as_ref();
let mut contains = false;
while let Some(n) = next {
if entry as *const _ == &**n as *const _ {
debug_assert!(!contains);
contains = true;
}
next = (*n.next_stack.get()).as_ref();
}
contains
});
// Unlink `entry` from the next node
let next = (*entry.next_stack.get()).take();
if let Some(next) = next.as_ref() {
(*next.prev_stack.get()) = *entry.prev_stack.get();
}
// Unlink `entry` from the prev node
if let Some(prev) = (*entry.prev_stack.get()).as_ref() {
*prev.next_stack.get() = next;
} else {
// It is the head
self.head = next;
}
// Unset the prev pointer
*entry.prev_stack.get() = ptr::null();
}
}
fn when(item: &Entry, _: &()) -> u64 {
item.when_internal().expect("invalid internal state")
}
}
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