Merge pull request #54 from Kerollmops/arccell-instead-of-rwlock

Prefer using ArcCell instead of RWLock for database updates

Cargo.toml

@@ -7,6 +7,7 @@ authors = ["Kerollmops <renault.cle@gmail.com>"]
 [dependencies]
 bincode = "1.0"
 byteorder = "1.2"
+crossbeam = "0.6"
 fst = "0.3"
 hashbrown = "0.1"
 lazy_static = "1.1"

src/database/database.rs

@@ -1,10 +1,11 @@
-use std::sync::{Arc, Mutex, RwLock, RwLockReadGuard};
+use std::sync::{Arc, Mutex};
 use std::error::Error;
 use std::path::Path;
 
 use rocksdb::rocksdb_options::{DBOptions, IngestExternalFileOptions, ColumnFamilyOptions};
 use rocksdb::rocksdb::{Writable, Snapshot};
 use rocksdb::{DB, DBVector, MergeOperands};
+use crossbeam::atomic::ArcCell;
 
 use crate::database::{DatabaseView, Update, Schema};
 use crate::database::{DATA_INDEX, DATA_SCHEMA};
@@ -17,7 +18,7 @@ pub struct Database {
     db: Mutex<Arc<DB>>,
 
     // This view is updated each time the DB ingests an update
-    view: RwLock<DatabaseView<Arc<DB>>>,
+    view: ArcCell<DatabaseView<Arc<DB>>>,
 }
 
 impl Database {
@@ -44,7 +45,7 @@ impl Database {
 
         let db = Arc::new(db);
         let snapshot = Snapshot::new(db.clone());
-        let view = RwLock::new(DatabaseView::new(snapshot)?);
+        let view = ArcCell::new(Arc::new(DatabaseView::new(snapshot)?));
 
         Ok(Database { db: Mutex::new(db), view })
     }
@@ -68,12 +69,12 @@ impl Database {
 
         let db = Arc::new(db);
         let snapshot = Snapshot::new(db.clone());
-        let view = RwLock::new(DatabaseView::new(snapshot)?);
+        let view = ArcCell::new(Arc::new(DatabaseView::new(snapshot)?));
 
         Ok(Database { db: Mutex::new(db), view })
     }
 
-    pub fn ingest_update_file(&self, update: Update) -> Result<(), Box<Error>> {
+    pub fn ingest_update_file(&self, update: Update) -> Result<Arc<DatabaseView<Arc<DB>>>, Box<Error>> {
         let snapshot = {
             // We must have a mutex here to ensure that update ingestions and compactions
             // are done atomatically and in the right order.
@@ -101,15 +102,10 @@ impl Database {
             Snapshot::new(db.clone())
         };
 
-        // Here we will block the view creation for the minimum amount of time:
-        // updating the DatabaseView itself with the new database snapshot
-        let view = DatabaseView::new(snapshot)?;
-        match self.view.write() {
-            Ok(mut lock) => *lock = view,
-            Err(e) => return Err(e.to_string().into()),
-        }
+        let view = Arc::new(DatabaseView::new(snapshot)?);
+        self.view.set(view.clone());
 
-        Ok(())
+        Ok(view)
     }
 
     pub fn get(&self, key: &[u8]) -> Result<Option<DBVector>, Box<Error>> {
@@ -123,8 +119,8 @@ impl Database {
         }
     }
 
-    pub fn view(&self) -> RwLockReadGuard<DatabaseView<Arc<DB>>> {
-        self.view.read().unwrap()
+    pub fn view(&self) -> Arc<DatabaseView<Arc<DB>>> {
+        self.view.get()
     }
 }