From f97168f80567f43e15cf236092703e6ae5d8dc2e Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Thu, 21 Sep 2023 15:32:25 +0200
Subject: garage_db: refactor transactions and add on_commit mechanism

---
 src/db/lib.rs | 75 +++++++++++++++++++++++++++++++----------------------------
 1 file changed, 40 insertions(+), 35 deletions(-)

(limited to 'src/db/lib.rs')

diff --git a/src/db/lib.rs b/src/db/lib.rs
index 22bd9364..fe44b01e 100644
--- a/src/db/lib.rs
+++ b/src/db/lib.rs
@@ -22,10 +22,15 @@ use std::sync::Arc;
 
 use err_derive::Error;
 
+pub(crate) type OnCommit = Vec<Box<dyn FnOnce()>>;
+
 #[derive(Clone)]
 pub struct Db(pub(crate) Arc<dyn IDb>);
 
-pub struct Transaction<'a>(&'a mut dyn ITx);
+pub struct Transaction<'a> {
+	tx: &'a mut dyn ITx,
+	on_commit: OnCommit,
+}
 
 #[derive(Clone)]
 pub struct Tree(Arc<dyn IDb>, usize);
@@ -85,7 +90,7 @@ impl Db {
 
 	pub fn transaction<R, E, F>(&self, fun: F) -> TxResult<R, E>
 	where
-		F: Fn(Transaction<'_>) -> TxResult<R, E>,
+		F: Fn(&mut Transaction<'_>) -> TxResult<R, E>,
 	{
 		let f = TxFn {
 			function: fun,
@@ -98,14 +103,17 @@ impl Db {
 			.expect("Transaction did not store result");
 
 		match tx_res {
-			Ok(()) => {
-				assert!(matches!(ret, Ok(_)));
-				ret
-			}
-			Err(TxError::Abort(())) => {
-				assert!(matches!(ret, Err(TxError::Abort(_))));
-				ret
-			}
+			Ok(on_commit) => match ret {
+				Ok(value) => {
+					on_commit.into_iter().for_each(|f| f());
+					Ok(value)
+				}
+				_ => unreachable!(),
+			},
+			Err(TxError::Abort(())) => match ret {
+				Err(TxError::Abort(e)) => Err(TxError::Abort(e)),
+				_ => unreachable!(),
+			},
 			Err(TxError::Db(e2)) => match ret {
 				// Ok was stored -> the error occured when finalizing
 				// transaction
@@ -139,7 +147,7 @@ impl Db {
 
 			let ex_tree = other.open_tree(&name)?;
 
-			let tx_res = self.transaction(|mut tx| {
+			let tx_res = self.transaction(|tx| {
 				let mut i = 0;
 				for item in ex_tree.iter().map_err(TxError::Abort)? {
 					let (k, v) = item.map_err(TxError::Abort)?;
@@ -149,7 +157,7 @@ impl Db {
 						println!("{}: imported {}", name, i);
 					}
 				}
-				tx.commit(i)
+				Ok(i)
 			});
 			let total = match tx_res {
 				Err(TxError::Db(e)) => return Err(e),
@@ -249,11 +257,11 @@ impl Tree {
 impl<'a> Transaction<'a> {
 	#[inline]
 	pub fn get<T: AsRef<[u8]>>(&self, tree: &Tree, key: T) -> TxOpResult<Option<Value>> {
-		self.0.get(tree.1, key.as_ref())
+		self.tx.get(tree.1, key.as_ref())
 	}
 	#[inline]
 	pub fn len(&self, tree: &Tree) -> TxOpResult<usize> {
-		self.0.len(tree.1)
+		self.tx.len(tree.1)
 	}
 
 	/// Returns the old value if there was one
@@ -264,21 +272,21 @@ impl<'a> Transaction<'a> {
 		key: T,
 		value: U,
 	) -> TxOpResult<Option<Value>> {
-		self.0.insert(tree.1, key.as_ref(), value.as_ref())
+		self.tx.insert(tree.1, key.as_ref(), value.as_ref())
 	}
 	/// Returns the old value if there was one
 	#[inline]
 	pub fn remove<T: AsRef<[u8]>>(&mut self, tree: &Tree, key: T) -> TxOpResult<Option<Value>> {
-		self.0.remove(tree.1, key.as_ref())
+		self.tx.remove(tree.1, key.as_ref())
 	}
 
 	#[inline]
 	pub fn iter(&self, tree: &Tree) -> TxOpResult<TxValueIter<'_>> {
-		self.0.iter(tree.1)
+		self.tx.iter(tree.1)
 	}
 	#[inline]
 	pub fn iter_rev(&self, tree: &Tree) -> TxOpResult<TxValueIter<'_>> {
-		self.0.iter_rev(tree.1)
+		self.tx.iter_rev(tree.1)
 	}
 
 	#[inline]
@@ -289,7 +297,7 @@ impl<'a> Transaction<'a> {
 	{
 		let sb = range.start_bound();
 		let eb = range.end_bound();
-		self.0.range(tree.1, get_bound(sb), get_bound(eb))
+		self.tx.range(tree.1, get_bound(sb), get_bound(eb))
 	}
 	#[inline]
 	pub fn range_rev<K, R>(&self, tree: &Tree, range: R) -> TxOpResult<TxValueIter<'_>>
@@ -299,19 +307,12 @@ impl<'a> Transaction<'a> {
 	{
 		let sb = range.start_bound();
 		let eb = range.end_bound();
-		self.0.range_rev(tree.1, get_bound(sb), get_bound(eb))
+		self.tx.range_rev(tree.1, get_bound(sb), get_bound(eb))
 	}
 
-	// ----
-
 	#[inline]
-	pub fn abort<R, E>(self, e: E) -> TxResult<R, E> {
-		Err(TxError::Abort(e))
-	}
-
-	#[inline]
-	pub fn commit<R, E>(self, r: R) -> TxResult<R, E> {
-		Ok(r)
+	pub fn on_commit<F: FnOnce() + 'static>(&mut self, f: F) {
+		self.on_commit.push(Box::new(f));
 	}
 }
 
@@ -348,7 +349,7 @@ pub(crate) trait IDb: Send + Sync {
 		high: Bound<&'r [u8]>,
 	) -> Result<ValueIter<'_>>;
 
-	fn transaction(&self, f: &dyn ITxFn) -> TxResult<(), ()>;
+	fn transaction(&self, f: &dyn ITxFn) -> TxResult<OnCommit, ()>;
 }
 
 pub(crate) trait ITx {
@@ -380,14 +381,14 @@ pub(crate) trait ITxFn {
 }
 
 pub(crate) enum TxFnResult {
-	Ok,
+	Ok(OnCommit),
 	Abort,
 	DbErr,
 }
 
 struct TxFn<F, R, E>
 where
-	F: Fn(Transaction<'_>) -> TxResult<R, E>,
+	F: Fn(&mut Transaction<'_>) -> TxResult<R, E>,
 {
 	function: F,
 	result: Cell<Option<TxResult<R, E>>>,
@@ -395,12 +396,16 @@ where
 
 impl<F, R, E> ITxFn for TxFn<F, R, E>
 where
-	F: Fn(Transaction<'_>) -> TxResult<R, E>,
+	F: Fn(&mut Transaction<'_>) -> TxResult<R, E>,
 {
 	fn try_on(&self, tx: &mut dyn ITx) -> TxFnResult {
-		let res = (self.function)(Transaction(tx));
+		let mut tx = Transaction {
+			tx,
+			on_commit: vec![],
+		};
+		let res = (self.function)(&mut tx);
 		let res2 = match &res {
-			Ok(_) => TxFnResult::Ok,
+			Ok(_) => TxFnResult::Ok(tx.on_commit),
 			Err(TxError::Abort(_)) => TxFnResult::Abort,
 			Err(TxError::Db(_)) => TxFnResult::DbErr,
 		};
-- 
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