Add `TMCell`
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/*
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* Created on Sat Jan 21 2023
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*
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* This file is a part of Skytable
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* Skytable (formerly known as TerrabaseDB or Skybase) is a free and open-source
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* NoSQL database written by Sayan Nandan ("the Author") with the
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* vision to provide flexibility in data modelling without compromising
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* on performance, queryability or scalability.
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*
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* Copyright (c) 2023, Sayan Nandan <ohsayan@outlook.com>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*
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*/
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use super::atm::{pin_unprotected, Atomic, Guard, Owned, Shared, ORD_REL};
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use core::ops::Deref;
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use parking_lot::{Mutex, MutexGuard};
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use std::marker::PhantomData;
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/// A [`TMCell`] provides atomic reads and serialized writes; the `static` is a CB hack
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pub struct TMCell<T: 'static> {
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a: Atomic<T>,
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g: Mutex<()>,
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}
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impl<T: 'static> TMCell<T> {
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pub fn new(v: T) -> Self {
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Self {
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a: Atomic::new_alloc(v),
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g: Mutex::new(()),
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}
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}
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pub fn begin_write_txn<'a, 'g>(&'a self, g: &'g Guard) -> TMCellWriteTxn<'a, 'g, T> {
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let wg = self.g.lock();
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let snapshot = self.a.ld_acq(g);
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let data: &'g T = unsafe {
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// UNSAFE(@ohsayan): first, non-null (TMCell is never null). second, the guard
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snapshot.deref()
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};
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TMCellWriteTxn::new(data, &self.a, wg)
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}
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pub fn begin_read_txn<'a, 'g>(&'a self, g: &'g Guard) -> TMCellReadTxn<'a, 'g, T> {
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let snapshot = self.a.ld_acq(g);
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let data: &'g T = unsafe {
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// UNSAFE(@ohsayan): non-null and the guard
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snapshot.deref()
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};
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TMCellReadTxn::new(data)
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}
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}
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impl<T> Drop for TMCell<T> {
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fn drop(&mut self) {
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unsafe {
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// UNSAFE(@ohsayan): Sole owner with mutable access
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let g = pin_unprotected();
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let shptr = self.a.ld_rlx(&g);
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g.defer_destroy(shptr);
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}
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}
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}
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pub struct TMCellReadTxn<'a, 'g, T: 'static> {
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d: &'g T,
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_m: PhantomData<&'a TMCell<T>>,
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}
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impl<'a, 'g, T> TMCellReadTxn<'a, 'g, T> {
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#[inline(always)]
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pub fn new(d: &'g T) -> Self {
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Self { d, _m: PhantomData }
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}
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#[inline(always)]
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pub fn read(&self) -> &'g T {
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self.d
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}
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}
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impl<'a, 'g, T: Copy> TMCellReadTxn<'a, 'g, T> {
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fn read_copy(&self) -> T {
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*self.d
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}
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}
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impl<'a, 'g, T> Deref for TMCellReadTxn<'a, 'g, T> {
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type Target = T;
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fn deref(&self) -> &'g Self::Target {
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self.d
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}
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}
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pub struct TMCellWriteTxn<'a, 'g, T: 'static> {
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d: &'g T,
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a: &'a Atomic<T>,
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g: MutexGuard<'a, ()>,
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}
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impl<'a, 'g, T> TMCellWriteTxn<'a, 'g, T> {
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#[inline(always)]
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pub fn new(d: &'g T, a: &'a Atomic<T>, g: MutexGuard<'a, ()>) -> Self {
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Self { d, a, g }
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}
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pub fn publish_commit(self, new: T, g: &'g Guard) {
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self._commit(new, g, |p| {
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unsafe {
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// UNSAFE(@ohsayan): Unlinked
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g.defer_destroy(p);
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}
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})
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}
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fn _commit<F, R>(self, new: T, g: &'g Guard, f: F) -> R
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where
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F: FnOnce(Shared<T>) -> R,
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{
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let new = Owned::new(new);
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let r = self.a.swap(new, ORD_REL, g);
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f(r)
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}
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#[inline(always)]
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pub fn read(&self) -> &'g T {
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self.d
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}
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}
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impl<'a, 'g, T: Copy> TMCellWriteTxn<'a, 'g, T> {
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fn read_copy(&self) -> T {
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*self.d
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}
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}
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impl<'a, 'g, T> Deref for TMCellWriteTxn<'a, 'g, T> {
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type Target = T;
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fn deref(&self) -> &'g Self::Target {
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self.d
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}
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}
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