feature: added blocking start for genservers

Cargo.toml

@@ -8,7 +8,7 @@ members = [
     "examples/ping_pong",
     "examples/ping_pong_threads",
     "examples/updater",
-    "examples/updater_threads",
+    "examples/updater_threads", "examples/blocking_genserver",
 ]
 
 [workspace.dependencies]

concurrency/src/tasks/gen_server.rs

@@ -38,6 +38,26 @@ impl<G: GenServer> GenServerHandle<G> {
         handle_clone
     }
 
+    pub(crate) fn new_blocking(mut initial_state: G::State) -> Self {
+        let (tx, mut rx) = mpsc::channel::<GenServerInMsg<G>>();
+        let handle = GenServerHandle { tx };
+        let mut gen_server: G = GenServer::new();
+        let handle_clone = handle.clone();
+        // Ignore the JoinHandle for now. Maybe we'll use it in the future
+        let _join_handle = rt::spawn_blocking(|| {
+            rt::block_on(async move {
+                if gen_server
+                    .run(&handle, &mut rx, &mut initial_state)
+                    .await
+                    .is_err()
+                {
+                    tracing::trace!("GenServer crashed")
+                };
+            })
+        });
+        handle_clone
+    }
+
     pub fn sender(&self) -> mpsc::Sender<GenServerInMsg<G>> {
         self.tx.clone()
     }
@@ -98,6 +118,15 @@ where
         GenServerHandle::new(initial_state)
     }
 
+    /// Tokio tasks depend on a coolaborative multitasking model. "work stealing" can't
+    /// happen if the task is blocking the thread. As such, for sync compute task
+    /// or other blocking tasks need to be in their own separate thread, and the OS
+    /// will manage them through hardware interrupts.
+    /// Start blocking provides such thread.
+    fn start_blocking(initial_state: Self::State) -> GenServerHandle<Self> {
+        GenServerHandle::new_blocking(initial_state)
+    }
+
     fn run(
         &mut self,
         handle: &GenServerHandle<Self>,
@@ -201,3 +230,136 @@ where
         state: &mut Self::State,
     ) -> impl std::future::Future<Output = CastResponse> + Send;
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tasks::send_after;
+    use std::{process::exit, thread, time::Duration};
+    struct BadlyBehavedTask;
+
+    #[derive(Clone)]
+    pub enum InMessage {
+        GetCount,
+        Stop,
+    }
+    #[derive(Clone)]
+    pub enum OutMsg {
+        Count(u64),
+    }
+
+    impl GenServer for BadlyBehavedTask {
+        type CallMsg = InMessage;
+        type CastMsg = ();
+        type OutMsg = ();
+        type State = ();
+        type Error = ();
+
+        fn new() -> Self {
+            Self {}
+        }
+
+        async fn handle_call(
+            &mut self,
+            _: Self::CallMsg,
+            _: &GenServerHandle<Self>,
+            _: &mut Self::State,
+        ) -> CallResponse<Self::OutMsg> {
+            CallResponse::Stop(())
+        }
+
+        async fn handle_cast(
+            &mut self,
+            _: Self::CastMsg,
+            _: &GenServerHandle<Self>,
+            _: &mut Self::State,
+        ) -> CastResponse {
+            rt::sleep(Duration::from_millis(20)).await;
+            thread::sleep(Duration::from_secs(2));
+            CastResponse::Stop
+        }
+    }
+
+    struct WellBehavedTask;
+
+    #[derive(Clone)]
+    struct CountState {
+        pub count: u64,
+    }
+
+    impl GenServer for WellBehavedTask {
+        type CallMsg = InMessage;
+        type CastMsg = ();
+        type OutMsg = OutMsg;
+        type State = CountState;
+        type Error = ();
+
+        fn new() -> Self {
+            Self {}
+        }
+
+        async fn handle_call(
+            &mut self,
+            message: Self::CallMsg,
+            _: &GenServerHandle<Self>,
+            state: &mut Self::State,
+        ) -> CallResponse<Self::OutMsg> {
+            match message {
+                InMessage::GetCount => CallResponse::Reply(OutMsg::Count(state.count)),
+                InMessage::Stop => CallResponse::Stop(OutMsg::Count(state.count)),
+            }
+        }
+
+        async fn handle_cast(
+            &mut self,
+            _: Self::CastMsg,
+            handle: &GenServerHandle<Self>,
+            state: &mut Self::State,
+        ) -> CastResponse {
+            state.count += 1;
+            println!("{:?}: good still alive", thread::current().id());
+            send_after(Duration::from_millis(100), handle.to_owned(), ());
+            CastResponse::NoReply
+        }
+    }
+
+    #[test]
+    pub fn badly_behaved_thread_non_blocking() {
+        let runtime = rt::Runtime::new().unwrap();
+        runtime.block_on(async move {
+            let mut badboy = BadlyBehavedTask::start(());
+            let _ = badboy.cast(()).await;
+            let mut goodboy = WellBehavedTask::start(CountState { count: 0 });
+            let _ = goodboy.cast(()).await;
+            rt::sleep(Duration::from_secs(1)).await;
+            let count = goodboy.call(InMessage::GetCount).await.unwrap();
+
+            match count {
+                OutMsg::Count(num) => {
+                    assert_ne!(num, 10);
+                }
+            }
+            goodboy.call(InMessage::Stop).await.unwrap();
+        });
+    }
+
+    #[test]
+    pub fn badly_behaved_thread() {
+        let runtime = rt::Runtime::new().unwrap();
+        runtime.block_on(async move {
+            let mut badboy = BadlyBehavedTask::start_blocking(());
+            let _ = badboy.cast(()).await;
+            let mut goodboy = WellBehavedTask::start(CountState { count: 0 });
+            let _ = goodboy.cast(()).await;
+            rt::sleep(Duration::from_secs(1)).await;
+            let count = goodboy.call(InMessage::GetCount).await.unwrap();
+
+            match count {
+                OutMsg::Count(num) => {
+                    assert_eq!(num, 10);
+                }
+            }
+            goodboy.call(InMessage::Stop).await.unwrap();
+        });
+    }
+}

concurrency/src/threads/gen_server.rs

@@ -98,6 +98,12 @@ where
         GenServerHandle::new(initial_state)
     }
 
+    /// We copy the same interface as tasks, but all threads can work
+    /// while blocking by default
+    fn start_blocking(initial_state: Self::State) -> GenServerHandle<Self> {
+        GenServerHandle::new(initial_state)
+    }
+
     fn run(
         &mut self,
         handle: &GenServerHandle<Self>,

examples/blocking_genserver/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "blocking_genserver"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+spawned-rt = { workspace = true }
+spawned-concurrency = { workspace = true }
+tracing = { workspace = true }
+
+[[bin]]
+name = "blocking_genserver"
+path = "main.rs"

examples/blocking_genserver/main.rs

@@ -0,0 +1,121 @@
+use spawned_rt::tasks as rt;
+use std::time::Duration;
+use std::{process::exit, thread};
+
+use spawned_concurrency::tasks::{
+    CallResponse, CastResponse, GenServer, GenServerHandle, send_after,
+};
+
+// We test a scenario with a badly behaved task
+struct BadlyBehavedTask;
+
+#[derive(Clone)]
+pub enum InMessage {
+    GetCount,
+    Stop,
+}
+#[derive(Clone)]
+pub enum OutMsg {
+    Count(u64),
+}
+
+impl GenServer for BadlyBehavedTask {
+    type CallMsg = InMessage;
+    type CastMsg = ();
+    type OutMsg = ();
+    type State = ();
+    type Error = ();
+
+    fn new() -> Self {
+        Self {}
+    }
+
+    async fn handle_call(
+        &mut self,
+        _: Self::CallMsg,
+        _: &GenServerHandle<Self>,
+        _: &mut Self::State,
+    ) -> CallResponse<Self::OutMsg> {
+        CallResponse::Stop(())
+    }
+
+    async fn handle_cast(
+        &mut self,
+        _: Self::CastMsg,
+        _: &GenServerHandle<Self>,
+        _: &mut Self::State,
+    ) -> CastResponse {
+        rt::sleep(Duration::from_millis(20)).await;
+        loop {
+            println!("{:?}: bad still alive", thread::current().id());
+            thread::sleep(Duration::from_millis(50));
+        }
+    }
+}
+
+struct WellBehavedTask;
+
+#[derive(Clone)]
+struct CountState {
+    pub count: u64,
+}
+
+impl GenServer for WellBehavedTask {
+    type CallMsg = InMessage;
+    type CastMsg = ();
+    type OutMsg = OutMsg;
+    type State = CountState;
+    type Error = ();
+
+    fn new() -> Self {
+        Self {}
+    }
+
+    async fn handle_call(
+        &mut self,
+        message: Self::CallMsg,
+        _: &GenServerHandle<Self>,
+        state: &mut Self::State,
+    ) -> CallResponse<Self::OutMsg> {
+        match message {
+            InMessage::GetCount => CallResponse::Reply(OutMsg::Count(state.count)),
+            InMessage::Stop => CallResponse::Stop(OutMsg::Count(state.count)),
+        }
+    }
+
+    async fn handle_cast(
+        &mut self,
+        _: Self::CastMsg,
+        handle: &GenServerHandle<Self>,
+        state: &mut Self::State,
+    ) -> CastResponse {
+        state.count += 1;
+        println!("{:?}: good still alive", thread::current().id());
+        send_after(Duration::from_millis(100), handle.to_owned(), ());
+        CastResponse::NoReply
+    }
+}
+
+/// Example of start_blocking to fix issues #8 https://github.com/lambdaclass/spawned/issues/8
+/// Tasks that block can block the entire tokio runtime (and other cooperative multitasking models)
+/// To fix this we implement start_blocking, which under the hood launches a new thread to deal with the issue
+pub fn main() {
+    rt::run(async move {
+        // If we change BadlyBehavedTask to start instead, it can stop the entire program
+        let mut badboy = BadlyBehavedTask::start_blocking(());
+        let _ = badboy.cast(()).await;
+        let mut goodboy = WellBehavedTask::start(CountState { count: 0 });
+        let _ = goodboy.cast(()).await;
+        rt::sleep(Duration::from_secs(1)).await;
+        let count = goodboy.call(InMessage::GetCount).await.unwrap();
+
+        match count {
+            OutMsg::Count(num) => {
+                assert!(num == 10);
+            }
+        }
+
+        goodboy.call(InMessage::Stop).await.unwrap();
+        exit(0);
+    })
+}

rt/src/tasks/mod.rs

@@ -9,12 +9,14 @@
 
 mod tokio;
 
+use ::tokio::runtime::Handle;
+
 use crate::tracing::init_tracing;
 
 pub use crate::tasks::tokio::mpsc;
 pub use crate::tasks::tokio::oneshot;
 pub use crate::tasks::tokio::sleep;
-pub use crate::tasks::tokio::{spawn, JoinHandle, Runtime};
+pub use crate::tasks::tokio::{spawn, spawn_blocking, JoinHandle, Runtime};
 use std::future::Future;
 
 pub fn run<F: Future>(future: F) -> F::Output {
@@ -23,3 +25,7 @@ pub fn run<F: Future>(future: F) -> F::Output {
     let rt = Runtime::new().unwrap();
     rt.block_on(future)
 }
+
+pub fn block_on<F: Future>(future: F) -> F::Output {
+    Handle::current().block_on(future)
+}

rt/src/tasks/tokio/mod.rs

@@ -4,6 +4,7 @@ pub mod oneshot;
 
 pub use tokio::{
     runtime::Runtime,
-    task::{spawn, JoinHandle},
+    task::{spawn, spawn_blocking, JoinHandle},
     time::sleep,
+    test,
 };

rt/src/threads/mod.rs

@@ -20,3 +20,12 @@ pub fn block_on<F: Future>(future: F) -> F::Output {
     let rt = Runtime::new().unwrap();
     rt.block_on(future)
 }
+
+/// Spawn blocking is the same as spawn for pure threaded usage.
+pub fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    spawn(f)
+}