feat: add async-std as an optional runtime for AsyncDB

Cargo.toml

@@ -22,13 +22,16 @@ rand = "0.8.5"
 snap = "1.0"
 
 errno = { optional = true, version = "0.2" }
-fs2 = {optional = true, version = "0.4.3"}
+fs2 = { optional = true, version = "0.4.3" }
 
-tokio = { optional = true, features = ["rt", "sync"], version = ">= 1.21" }
+tokio = { optional = true, features = ["rt", "sync"], version = "1.39.3" }
+async-std = { optional = true, version = "1.12.0" }
 
 [features]
 default = ["fs"]
-async = ["tokio"]
+async = ["asyncdb-tokio"]
+asyncdb-tokio = ["tokio"]
+asyncdb-async-std = ["async-std"]
 fs = ["errno", "fs2"]
 
 [dev-dependencies]
@@ -46,7 +49,8 @@ members = [
     "examples/leveldb-tool",
     "examples/word-analyze",
     "examples/stresstest",
-    "examples/asyncdb",
+    "examples/asyncdb-tokio",
+    "examples/asyncdb-async-std",
     "examples/mcpe",
     "examples/kvserver",
 ]

examples/asyncdb-async-std/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "asyncdb-async-std"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+async-std = { version = "1.12.0", features = ["attributes"] }
+rusty-leveldb = { path = "../../", features = ["asyncdb-async-std"] }

examples/asyncdb-async-std/src/main.rs

@@ -0,0 +1,38 @@
+use rusty_leveldb::{AsyncDB, Options, Status, StatusCode};
+
+#[async_std::main]
+async fn main() {
+    let adb = AsyncDB::new("testdb", Options::default()).unwrap();
+
+    adb.put("Hello".as_bytes().to_owned(), "World".as_bytes().to_owned())
+        .await
+        .expect("put()");
+
+    let r = adb.get("Hello".as_bytes().to_owned()).await;
+    assert_eq!(r, Ok(Some("World".as_bytes().to_owned())));
+
+    let snapshot = adb.get_snapshot().await.expect("get_snapshot()");
+
+    adb.delete("Hello".as_bytes().to_owned())
+        .await
+        .expect("delete()");
+
+    // A snapshot allows us to travel back in time before the deletion.
+    let r2 = adb.get_at(snapshot, "Hello".as_bytes().to_owned()).await;
+    assert_eq!(r2, Ok(Some("World".as_bytes().to_owned())));
+
+    // Once dropped, a snapshot cannot be used anymore.
+    adb.drop_snapshot(snapshot).await.expect("drop_snapshot()");
+
+    let r3 = adb.get_at(snapshot, "Hello".as_bytes().to_owned()).await;
+    assert_eq!(
+        r3,
+        Err(Status {
+            code: StatusCode::AsyncError,
+            err: "Unknown snapshot reference: this is a bug".to_string()
+        })
+    );
+
+    adb.flush().await.expect("flush()");
+    adb.close().await.expect("close()");
+}

examples/asyncdb/Cargo.toml → examples/asyncdb-tokio/Cargo.toml

@@ -1,10 +1,10 @@
 [package]
-name = "asyncdb"
+name = "asyncdb-tokio"
 version = "0.1.0"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-tokio = { version = "1.21", features = ["rt", "macros" ] }
-rusty-leveldb = { path = "../../", features = ["async"] }
+tokio = { version = "1.21", features = ["rt", "macros"] }
+rusty-leveldb = { path = "../../", features = ["asyncdb-tokio"] }

src/asyncdb.rs

@@ -1,20 +1,17 @@
 use std::collections::hash_map::HashMap;
-use std::path::Path;
-use std::sync::Arc;
 
-use crate::{Options, Result, Status, StatusCode, WriteBatch, DB};
+use crate::{
+    send_response, send_response_result, AsyncDB, Message, Result, Status, StatusCode, WriteBatch,
+    DB,
+};
 
-use tokio::sync::mpsc;
-use tokio::sync::oneshot;
-use tokio::task::{spawn_blocking, JoinHandle};
-
-const CHANNEL_BUFFER_SIZE: usize = 32;
+pub(crate) const CHANNEL_BUFFER_SIZE: usize = 32;
 
 #[derive(Clone, Copy)]
 pub struct SnapshotRef(usize);
 
 /// A request sent to the database thread.
-enum Request {
+pub(crate) enum Request {
     Close,
     Put { key: Vec<u8>, val: Vec<u8> },
     Delete { key: Vec<u8> },
@@ -28,42 +25,14 @@ enum Request {
 }
 
 /// A response received from the database thread.
-enum Response {
+pub(crate) enum Response {
     OK,
     Error(Status),
     Value(Option<Vec<u8>>),
     Snapshot(SnapshotRef),
 }
 
-/// Contains both a request and a back-channel for the reply.
-struct Message {
-    req: Request,
-    resp_channel: oneshot::Sender<Response>,
-}
-
-/// `AsyncDB` makes it easy to use LevelDB in a tokio runtime.
-/// The methods follow very closely the main API (see `DB` type). Iteration is not yet implemented.
-///
-/// TODO: Make it work in other runtimes as well. This is a matter of adapting the blocking thread
-/// mechanism as well as the channel types.
-#[derive(Clone)]
-pub struct AsyncDB {
-    jh: Arc<JoinHandle<()>>,
-    send: mpsc::Sender<Message>,
-}
-
 impl AsyncDB {
-    /// Create a new or open an existing database.
-    pub fn new<P: AsRef<Path>>(name: P, opts: Options) -> Result<AsyncDB> {
-        let db = DB::open(name, opts)?;
-        let (send, recv) = mpsc::channel(CHANNEL_BUFFER_SIZE);
-        let jh = spawn_blocking(move || AsyncDB::run_server(db, recv));
-        Ok(AsyncDB {
-            jh: Arc::new(jh),
-            send,
-        })
-    }
-
     pub async fn close(&self) -> Result<()> {
         let r = self.process_request(Request::Close).await?;
         match r {
@@ -182,104 +151,79 @@ impl AsyncDB {
         }
     }
 
-    async fn process_request(&self, req: Request) -> Result<Response> {
-        let (tx, rx) = oneshot::channel();
-        let m = Message {
-            req,
-            resp_channel: tx,
-        };
-        if let Err(e) = self.send.send(m).await {
-            return Err(Status {
-                code: StatusCode::AsyncError,
-                err: e.to_string(),
-            });
-        }
-        let resp = rx.await;
-        match resp {
-            Err(e) => Err(Status {
-                code: StatusCode::AsyncError,
-                err: e.to_string(),
-            }),
-            Ok(r) => Ok(r),
-        }
-    }
-
-    fn run_server(mut db: DB, mut recv: mpsc::Receiver<Message>) {
+    pub(crate) fn run_server(mut db: DB, mut recv: impl ReceiverExt<Message>) {
         let mut snapshots = HashMap::new();
         let mut snapshot_counter: usize = 0;
 
         while let Some(message) = recv.blocking_recv() {
             match message.req {
                 Request::Close => {
-                    message.resp_channel.send(Response::OK).ok();
+                    send_response(message.resp_channel, Response::OK);
                     recv.close();
                     return;
                 }
                 Request::Put { key, val } => {
                     let ok = db.put(&key, &val);
-                    send_response(message.resp_channel, ok);
+                    send_response_result(message.resp_channel, ok);
                 }
                 Request::Delete { key } => {
                     let ok = db.delete(&key);
-                    send_response(message.resp_channel, ok);
+                    send_response_result(message.resp_channel, ok);
                 }
                 Request::Write { batch, sync } => {
                     let ok = db.write(batch, sync);
-                    send_response(message.resp_channel, ok);
+                    send_response_result(message.resp_channel, ok);
                 }
                 Request::Flush => {
                     let ok = db.flush();
-                    send_response(message.resp_channel, ok);
+                    send_response_result(message.resp_channel, ok);
                 }
                 Request::GetAt { snapshot, key } => {
                     let snapshot_id = snapshot.0;
                     if let Some(snapshot) = snapshots.get(&snapshot_id) {
                         let ok = db.get_at(snapshot, &key);
                         match ok {
                             Err(e) => {
-                                message.resp_channel.send(Response::Error(e)).ok();
+                                send_response(message.resp_channel, Response::Error(e));
                             }
                             Ok(v) => {
-                                message.resp_channel.send(Response::Value(v)).ok();
+                                send_response(message.resp_channel, Response::Value(v));
                             }
                         };
                     } else {
-                        message
-                            .resp_channel
-                            .send(Response::Error(Status {
+                        send_response(
+                            message.resp_channel,
+                            Response::Error(Status {
                                 code: StatusCode::AsyncError,
                                 err: "Unknown snapshot reference: this is a bug".to_string(),
-                            }))
-                            .ok();
+                            }),
+                        );
                     }
                 }
                 Request::Get { key } => {
                     let r = db.get(&key);
-                    message.resp_channel.send(Response::Value(r)).ok();
+                    send_response(message.resp_channel, Response::Value(r));
                 }
                 Request::GetSnapshot => {
                     snapshots.insert(snapshot_counter, db.get_snapshot());
                     let sref = SnapshotRef(snapshot_counter);
                     snapshot_counter += 1;
-                    message.resp_channel.send(Response::Snapshot(sref)).ok();
+                    send_response(message.resp_channel, Response::Snapshot(sref));
                 }
                 Request::DropSnapshot { snapshot } => {
                     snapshots.remove(&snapshot.0);
-                    send_response(message.resp_channel, Ok(()));
+                    send_response_result(message.resp_channel, Ok(()));
                 }
                 Request::CompactRange { from, to } => {
                     let ok = db.compact_range(&from, &to);
-                    send_response(message.resp_channel, ok);
+                    send_response_result(message.resp_channel, ok);
                 }
             }
         }
     }
 }
 
-fn send_response(ch: oneshot::Sender<Response>, result: Result<()>) {
-    if let Err(e) = result {
-        ch.send(Response::Error(e)).ok();
-    } else {
-        ch.send(Response::OK).ok();
-    }
+pub(crate) trait ReceiverExt<T> {
+    fn blocking_recv(&mut self) -> Option<T>;
+    fn close(&mut self);
 }

src/asyncdb_async_std.rs

@@ -0,0 +1,79 @@
+use std::path::Path;
+use std::sync::Arc;
+
+use async_std::channel;
+use async_std::task::{spawn_blocking, JoinHandle};
+
+use crate::asyncdb::{ReceiverExt, Request, Response, CHANNEL_BUFFER_SIZE};
+use crate::{Options, Result, Status, StatusCode, DB};
+
+pub(crate) struct Message {
+    pub(crate) req: Request,
+    pub(crate) resp_channel: channel::Sender<Response>,
+}
+/// `AsyncDB` makes it easy to use LevelDB in a async-std runtime.
+/// The methods follow very closely the main API (see `DB` type). Iteration is not yet implemented.
+#[derive(Clone)]
+pub struct AsyncDB {
+    jh: Arc<JoinHandle<()>>,
+    send: channel::Sender<Message>,
+}
+
+impl AsyncDB {
+    /// Create a new or open an existing database.
+    pub fn new<P: AsRef<Path>>(name: P, opts: Options) -> Result<AsyncDB> {
+        let db = DB::open(name, opts)?;
+
+        let (send, recv) = channel::bounded(CHANNEL_BUFFER_SIZE);
+        let jh = spawn_blocking(move || AsyncDB::run_server(db, recv));
+        Ok(AsyncDB {
+            jh: Arc::new(jh),
+            send,
+        })
+    }
+
+    pub(crate) async fn process_request(&self, req: Request) -> Result<Response> {
+        let (tx, rx) = channel::bounded(1);
+
+        let m = Message {
+            req,
+            resp_channel: tx,
+        };
+        if let Err(e) = self.send.send(m).await {
+            return Err(Status {
+                code: StatusCode::AsyncError,
+                err: e.to_string(),
+            });
+        }
+        let resp = rx.recv().await;
+        match resp {
+            Err(e) => Err(Status {
+                code: StatusCode::AsyncError,
+                err: e.to_string(),
+            }),
+            Ok(r) => Ok(r),
+        }
+    }
+}
+
+pub(crate) fn send_response_result(ch: channel::Sender<Response>, result: Result<()>) {
+    if let Err(e) = result {
+        ch.try_send(Response::Error(e)).ok();
+    } else {
+        ch.try_send(Response::OK).ok();
+    }
+}
+
+pub(crate) fn send_response(ch: channel::Sender<Response>, res: Response) {
+    ch.send_blocking(res).ok();
+}
+
+impl<T> ReceiverExt<T> for channel::Receiver<T> {
+    fn blocking_recv(&mut self) -> Option<T> {
+        self.recv_blocking().ok()
+    }
+
+    fn close(&mut self) {
+        channel::Receiver::close(self);
+    }
+}