safer sqlite

cozo-core/src/storage/sqlite.rs

@@ -2,8 +2,11 @@
  * Copyright 2022, The Cozo Project Authors. Licensed under MPL-2.0.
  */
 
+use std::sync::{Arc, RwLock, RwLockReadGuard, RwLockWriteGuard};
+
 use ::sqlite::Connection;
-use miette::{miette, IntoDiagnostic, Result, WrapErr};
+use either::{Either, Left, Right};
+use miette::{bail, miette, IntoDiagnostic, Result, WrapErr};
 use sqlite::{State, Statement};
 
 use crate::data::tuple::Tuple;
@@ -12,12 +15,13 @@ use crate::storage::{Storage, StoreTx};
 
 /// The Sqlite storage engine
 pub struct SqliteStorage {
-    path: String,
+    lock: Arc<RwLock<()>>,
+    name: String,
 }
 
 /// create a sqlite backed database. `:memory:` is not OK.
 pub fn new_cozo_sqlite(path: String) -> Result<crate::Db<SqliteStorage>> {
-    let connection = sqlite::open(&path).into_diagnostic()?;
+    let conn = sqlite::open(&path).into_diagnostic()?;
     let query = r#"
         create table if not exists cozo
         (
@@ -25,41 +29,55 @@ pub fn new_cozo_sqlite(path: String) -> Result<crate::Db<SqliteStorage>> {
             v BLOB
         );
     "#;
-    let mut statement = connection.prepare(query).unwrap();
+    let mut statement = conn.prepare(query).unwrap();
     while statement.next().into_diagnostic()? != State::Done {}
 
-    let ret = crate::Db::new(SqliteStorage { path })?;
+    let ret = crate::Db::new(SqliteStorage {
+        lock: Arc::new(Default::default()),
+        name: path,
+    })?;
 
     ret.initialize()?;
     Ok(ret)
 }
 
-impl Storage<'_> for SqliteStorage {
-    type Tx = SqliteTx;
-
-    fn transact(&'_ self, _write: bool) -> Result<Self::Tx> {
-        let conn = sqlite::open(&self.path).into_diagnostic()?;
-        {
-            let query = r#"begin;"#;
-            let mut statement = conn.prepare(query).unwrap();
-            while statement.next().unwrap() != State::Done {}
+impl<'s> Storage<'s> for SqliteStorage {
+    type Tx = SqliteTx<'s>;
+
+    fn transact(&'s self, write: bool) -> Result<Self::Tx> {
+        let conn = sqlite::open(&self.name).into_diagnostic()?;
+        let lock = if write {
+            Right(self.lock.write().unwrap())
+        } else {
+            Left(self.lock.read().unwrap())
+        };
+        if write {
+            let mut stmt = conn.prepare("begin;").into_diagnostic()?;
+            while stmt.next().into_diagnostic()? != State::Done {}
         }
-
-        Ok(SqliteTx { conn })
+        Ok(SqliteTx {
+            lock,
+            conn,
+            committed: false,
+        })
     }
 
     fn del_range(&'_ self, lower: &[u8], upper: &[u8]) -> Result<()> {
         let lower_b = lower.to_vec();
         let upper_b = upper.to_vec();
-        let path = self.path.clone();
-        let connection = sqlite::open(path).unwrap();
         let query = r#"
                 delete from cozo where k >= ? and k < ?;
             "#;
-        let mut statement = connection.prepare(query).unwrap();
-        statement.bind((1, &lower_b as &[u8])).unwrap();
-        statement.bind((2, &upper_b as &[u8])).unwrap();
-        while statement.next().unwrap() != State::Done {}
+        let lock = self.lock.clone();
+        let name = self.name.clone();
+        std::thread::spawn(move || {
+            let _locked = lock.write().unwrap();
+            let conn = sqlite::open(&name).unwrap();
+            let mut statement = conn.prepare(query).unwrap();
+            statement.bind((1, &lower_b as &[u8])).unwrap();
+            statement.bind((2, &upper_b as &[u8])).unwrap();
+            while statement.next().unwrap() != State::Done {}
+        });
         Ok(())
     }
 
@@ -68,15 +86,29 @@ impl Storage<'_> for SqliteStorage {
     }
 }
 
-pub struct SqliteTx {
+pub struct SqliteTx<'a> {
+    lock: Either<RwLockReadGuard<'a, ()>, RwLockWriteGuard<'a, ()>>,
     conn: Connection,
+    committed: bool,
 }
 
-impl<'s> StoreTx<'s> for SqliteTx {
+impl Drop for SqliteTx<'_> {
+    fn drop(&mut self) {
+        if let Right(RwLockWriteGuard { .. }) = self.lock {
+            if !self.committed {
+                let query = r#"rollback;"#;
+                let _ = self.conn.execute(query);
+            }
+        }
+    }
+}
+
+impl<'s> StoreTx<'s> for SqliteTx<'s> {
     fn get(&self, key: &[u8], _for_update: bool) -> Result<Option<Vec<u8>>> {
         let query = r#"
                 select v from cozo where k = ?;
             "#;
+
         let mut statement = self.conn.prepare(query).unwrap();
         statement.bind((1, key)).unwrap();
         Ok(match statement.next().into_diagnostic()? {
@@ -93,6 +125,7 @@ impl<'s> StoreTx<'s> for SqliteTx {
                 insert into cozo(k, v) values (?, ?)
                 on conflict(k) do update set v=excluded.v;
             "#;
+
         let mut statement = self.conn.prepare(query).unwrap();
         statement.bind((1, key)).unwrap();
         statement.bind((2, val)).unwrap();
@@ -112,6 +145,7 @@ impl<'s> StoreTx<'s> for SqliteTx {
         let mut statement = self.conn.prepare(query).unwrap();
         statement.bind((1, key)).unwrap();
         while statement.next().into_diagnostic()? != State::Done {}
+
         Ok(())
     }
 
@@ -128,9 +162,16 @@ impl<'s> StoreTx<'s> for SqliteTx {
     }
 
     fn commit(&mut self) -> Result<()> {
-        let query = r#"commit;"#;
-        let mut statement = self.conn.prepare(query).unwrap();
-        while statement.next().unwrap() != State::Done {}
+        if let Right(RwLockWriteGuard { .. }) = self.lock {
+            if !self.committed {
+                let query = r#"commit;"#;
+                let mut statement = self.conn.prepare(query).unwrap();
+                while statement.next().into_diagnostic()? != State::Done {}
+                self.committed = true;
+            } else {
+                bail!("multiple commits")
+            }
+        }
         Ok(())
     }