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use parking_lot::Mutex;
use crate::history::History;
use crate::{Mvcc,Transaction,TxnId};
use guest_cell::{GuestCell,Guest,id::{Id,UniqueId}};
use std::sync::Arc;
use std::hash::Hash;
use std::borrow::Borrow;
use std::ops::{Index,IndexMut};
use std::marker::PhantomData;
pub struct MvccCell<T:?Sized>(pub(crate) Arc<MvccBox<T>>);
impl<T:?Sized> Clone for MvccCell<T> {
fn clone(&self)->Self { MvccCell(Arc::clone(&self.0)) }
}
impl<T:?Sized> MvccCell<T> {
pub fn new(mvcc: &Mvcc, init: Box<T>)->Self {
MvccCell(MvccBox::new(mvcc, init))
}
pub(crate) fn erase<'a>(&self)->ErasedCell<'a> where T:'a {
ErasedCell(Arc::clone(&self.0) as Arc<dyn 'a + Erased>)
}
}
pub(crate) struct MvccBox<T:?Sized> {
pub(crate) mvcc_id: Id,
pub(crate) history: Mutex<History<Box<T>>>,
pub(crate) pending: GuestCell<T>,
phantom: PhantomData<std::sync::RwLock<T>>,
}
impl<T:?Sized> MvccBox<T> {
pub fn new(mvcc: &Mvcc, init:Box<T>)->Arc<Self> {
Arc::new(MvccBox {
mvcc_id: mvcc.id(),
history: Mutex::new(History::new(init)),
pending: GuestCell::default(),
phantom: PhantomData,
})
}
fn pending_access(self: &Arc<Self>)->PendingAccessor<T> {
PendingAccessor(Arc::clone(self))
}
}
impl<'a, T:'a + ?Sized> Index<&'_ MvccCell<T>> for Transaction<'a> {
type Output = T;
fn index(&self, cell: &MvccCell<T>)->&T {
let txn = self;
txn.visible.lock().insert(cell.erase());
txn.pending
.get(cell.0.pending_access())
.unwrap_or_else(|| txn.get_committed_raw(cell))
}
}
impl<'a, T:'a + ?Sized> IndexMut<&'_ MvccCell<T>>
for Transaction<'a>
where Box<T>: Clone
{
fn index_mut(&mut self, cell:&MvccCell<T>)->&mut T {
let txn = self;
txn.visible.get_mut().insert(cell.erase());
txn.pending.get_or_init_mut(
cell.0.pending_access(),
|| cell.0.history.lock().lookup(*txn.seq).clone()
)
}
}
impl<'a> Transaction<'a> {
pub fn replace<T:'a+?Sized>(&mut self, cell:&MvccCell<T>, val: Box<T>)->Option<Box<T>> {
self.visible.get_mut().insert(cell.erase());
self.pending.set(cell.0.pending_access(), val)
}
pub fn revert<T:'a+?Sized>(&mut self, cell:&MvccCell<T>)->Option<Box<T>> {
self.visible.get_mut().insert(cell.erase());
self.pending.take(cell.0.pending_access())
}
pub fn get_committed<T:'a+?Sized>(&self, cell: &MvccCell<T>)->&T {
self.visible.lock().insert(cell.erase());
self.get_committed_raw(cell)
}
fn get_committed_raw<T:'a+?Sized>(&self, cell: &MvccCell<T>)->&T {
let guard = cell.0.history.lock();
let result: *const T = &***guard.lookup(*self.seq) as *const T;
unsafe { &* result }
}
}
pub(crate) trait Erased {
fn last_changed(&self)->TxnId;
fn commit<'a>(self: Arc<Self>, guard: &mut UniqueId, seq:TxnId, txn: &mut Guest<'a>) where Self:'a;
}
impl<T:?Sized> Erased for MvccBox<T> {
fn last_changed(&self)->TxnId {
self.history.lock().current()
}
fn commit<'a>(self: Arc<Self>, guard: &mut UniqueId, seq: TxnId, txn: &mut Guest<'a>) where Self:'a {
assert_eq!(**guard, self.mvcc_id);
let Some(val) = txn.take(self.pending_access()) else { return };
self.history.lock().push(seq, val);
}
}
struct PendingAccessor<T:?Sized>(Arc<MvccBox<T>>);
impl<T:?Sized> Borrow<GuestCell<T>> for PendingAccessor<T> {
fn borrow(&self)->&GuestCell<T> {
&self.0.pending
}
}
unsafe impl<T:?Sized> guest_cell::IndirectGuestCell for PendingAccessor<T> {
type Inner = T;
}
pub(crate) struct ErasedCell<'a>(pub Arc<dyn 'a + Erased>);
impl Eq for ErasedCell<'_> {}
impl PartialEq for ErasedCell<'_> {
fn eq(&self, rhs:&Self)->bool {
Arc::as_ptr(&self.0) == Arc::as_ptr(&rhs.0)
}
}
impl Hash for ErasedCell<'_> {
fn hash<H: std::hash::Hasher>(&self, hasher:&mut H) {
Arc::as_ptr(&self.0).hash(hasher)
}
}