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[rm-sled] Make proper use of pinning in LMDB adapter + comment unsafe

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This commit is contained in:
Alex Auvolat 2024-03-08 17:39:17 +01:00
parent b942949940
commit 32aa246300
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GPG key ID: 0E496D15096376BE
2 changed files with 47 additions and 25 deletions
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28
src/db/lmdb_adapter.rs
View file

@ -3,6 +3,7 @@ use core::ptr::NonNull;
use std::collections::HashMap;
use std::convert::TryInto;
use std::pin::Pin;
use std::sync::{Arc, RwLock};
use heed::types::ByteSlice;
@ -319,12 +320,20 @@ where
where
F: FnOnce(&'a RoTxn<'a>) -> Result<I>,
{
let mut res = TxAndIterator { tx, iter: None };
let res = TxAndIterator { tx, iter: None };
let mut boxed = Box::pin(res);
let tx = unsafe { NonNull::from(&res.tx).as_ref() };
res.iter = Some(iterfun(tx)?);
// This unsafe allows us to bypass lifetime checks
let tx = unsafe { NonNull::from(&boxed.tx).as_ref() };
let iter = iterfun(tx)?;
Ok(Box::new(res))
let mut_ref = Pin::as_mut(&mut boxed);
// This unsafe allows us to write in a field of the pinned struct
unsafe {
Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
}
Ok(Box::new(TxAndIteratorPin(boxed)))
}
}
@ -338,14 +347,21 @@ where
}
}
impl<'a, I> Iterator for TxAndIterator<'a, I>
struct TxAndIteratorPin<'a, I>(Pin<Box<TxAndIterator<'a, I>>>)
where
I: Iterator<Item = IteratorItem<'a>> + 'a;
impl<'a, I> Iterator for TxAndIteratorPin<'a, I>
where
I: Iterator<Item = IteratorItem<'a>> + 'a,
{
type Item = Result<(Value, Value)>;
fn next(&mut self) -> Option<Self::Item> {
match self.iter.as_mut().unwrap().next() {
let mut_ref = Pin::as_mut(&mut self.0);
// This unsafe allows us to mutably access the iterator field
let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
match next {
None => None,
Some(Err(e)) => Some(Err(e.into())),
Some(Ok((k, v))) => Some(Ok((k.to_vec(), v.to_vec()))),

44
src/db/sqlite_adapter.rs
View file

@ -444,17 +444,23 @@ impl<'a> DbValueIterator<'a> {
let mut boxed = Box::pin(res);
trace!("make iterator with sql: {}", sql);
// This unsafe allows us to bypass lifetime checks
let db = unsafe { NonNull::from(&boxed.db).as_ref() };
let stmt = db.db.prepare(sql)?;
let mut_ref = Pin::as_mut(&mut boxed);
// This unsafe allows us to write in a field of the pinned struct
unsafe {
let db = NonNull::from(&boxed.db);
let stmt = db.as_ref().db.prepare(sql)?;
let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut boxed);
Pin::get_unchecked_mut(mut_ref).stmt = Some(stmt);
}
let mut stmt = NonNull::from(&boxed.stmt);
let iter = stmt.as_mut().as_mut().unwrap().query(args)?;
// This unsafe allows us to bypass lifetime checks
let stmt = unsafe { NonNull::from(&boxed.stmt).as_mut() };
let iter = stmt.as_mut().unwrap().query(args)?;
let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut boxed);
let mut_ref = Pin::as_mut(&mut boxed);
// This unsafe allows us to write in a field of the pinned struct
unsafe {
Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
}
@ -476,10 +482,9 @@ impl<'a> Iterator for DbValueIteratorPin<'a> {
type Item = Result<(Value, Value)>;
fn next(&mut self) -> Option<Self::Item> {
let next = unsafe {
let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut self.0);
Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next()
};
let mut_ref = Pin::as_mut(&mut self.0);
// This unsafe allows us to mutably access the iterator field
let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
let row = match next {
Err(e) => return Some(Err(e.into())),
Ok(None) => return None,
@ -522,11 +527,13 @@ impl<'a> TxValueIterator<'a> {
let mut boxed = Box::pin(res);
trace!("make iterator with sql: {}", sql);
unsafe {
let mut stmt = NonNull::from(&boxed.stmt);
let iter = stmt.as_mut().query(args)?;
// This unsafe allows us to bypass lifetime checks
let stmt = unsafe { NonNull::from(&boxed.stmt).as_mut() };
let iter = stmt.query(args)?;
let mut_ref: Pin<&mut TxValueIterator<'a>> = Pin::as_mut(&mut boxed);
let mut_ref = Pin::as_mut(&mut boxed);
// This unsafe allows us to write in a field of the pinned struct
unsafe {
Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
}
@ -547,10 +554,9 @@ impl<'a> Iterator for TxValueIteratorPin<'a> {
type Item = TxOpResult<(Value, Value)>;
fn next(&mut self) -> Option<Self::Item> {
let next = unsafe {
let mut_ref: Pin<&mut TxValueIterator<'a>> = Pin::as_mut(&mut self.0);
Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next()
};
let mut_ref = Pin::as_mut(&mut self.0);
// This unsafe allows us to mutably access the iterator field
let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
let row = match next {
Err(e) => return Some(Err(e.into())),
Ok(None) => return None,