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Merged
ElFantasma merged 3 commits into from
Aug 18, 2025
Merged

Remove GenServer clone on message reception #42

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0c8e7fb
Borrowing self instead of moving
ElFantasma Aug 15, 2025
b634cbf
Removing invalid example
ElFantasma Aug 15, 2025
af1cbd3
Style fix
ElFantasma Aug 15, 2025
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9 changes: 0 additions & 9 deletions Cargo.lock
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1 change: 0 additions & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@ members = [
"examples/bank",
"examples/bank_threads",
"examples/name_server",
"examples/name_server_with_error",
"examples/ping_pong",
"examples/ping_pong_threads",
"examples/updater",
Expand Down
97 changes: 40 additions & 57 deletions concurrency/src/tasks/gen_server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -112,13 +112,13 @@ pub enum GenServerInMsg<G: GenServer> {
}

pub enum CallResponse<G: GenServer> {
Reply(G, G::OutMsg),
Reply(G::OutMsg),
Unused,
Stop(G::OutMsg),
}

pub enum CastResponse<G: GenServer> {
NoReply(G),
pub enum CastResponse {
NoReply,
Unused,
Stop,
}
Expand All @@ -128,7 +128,7 @@ pub enum InitResult<G: GenServer> {
NoSuccess(G),
}

pub trait GenServer: Send + Sized + Clone {
pub trait GenServer: Send + Sized {
type CallMsg: Clone + Send + Sized + Sync;
type CastMsg: Clone + Send + Sized + Sync;
type OutMsg: Send + Sized;
Expand All @@ -154,7 +154,7 @@ pub trait GenServer: Send + Sized + Clone {
) -> impl Future<Output = Result<(), GenServerError>> + Send {
async {
let res = match self.init(handle).await {
Ok(Success(new_state)) => new_state.main_loop(handle, rx).await,
Ok(Success(new_state)) => Ok(new_state.main_loop(handle, rx).await),
Ok(NoSuccess(intermediate_state)) => {
// new_state is NoSuccess, this means the initialization failed, but the error was handled
// in callback. No need to report the error.
Expand Down Expand Up @@ -191,53 +191,44 @@ pub trait GenServer: Send + Sized + Clone {
mut self,
handle: &GenServerHandle<Self>,
rx: &mut mpsc::Receiver<GenServerInMsg<Self>>,
) -> impl Future<Output = Result<Self, GenServerError>> + Send {
) -> impl Future<Output = Self> + Send {
async {
loop {
let (new_state, cont) = self.receive(handle, rx).await?;
self = new_state;
if !cont {
if !self.receive(handle, rx).await {
break;
}
}
tracing::trace!("Stopping GenServer");
Ok(self)
self
}
}

fn receive(
self,
&mut self,
handle: &GenServerHandle<Self>,
rx: &mut mpsc::Receiver<GenServerInMsg<Self>>,
) -> impl Future<Output = Result<(Self, bool), GenServerError>> + Send {
) -> impl Future<Output = bool> + Send {
async move {
let message = rx.recv().await;

// Save current state in case of a rollback
let state_clone = self.clone();

let (keep_running, new_state) = match message {
let keep_running = match message {
Some(GenServerInMsg::Call { sender, message }) => {
let (keep_running, new_state, response) =
let (keep_running, response) =
match AssertUnwindSafe(self.handle_call(message, handle))
.catch_unwind()
.await
{
Ok(response) => match response {
CallResponse::Reply(new_state, response) => {
(true, new_state, Ok(response))
}
CallResponse::Stop(response) => (false, state_clone, Ok(response)),
CallResponse::Reply(response) => (true, Ok(response)),
CallResponse::Stop(response) => (false, Ok(response)),
CallResponse::Unused => {
tracing::error!("GenServer received unexpected CallMessage");
(false, state_clone, Err(GenServerError::CallMsgUnused))
(false, Err(GenServerError::CallMsgUnused))
}
},
Err(error) => {
tracing::error!(
"Error in callback, reverting state - Error: '{error:?}'"
);
(true, state_clone, Err(GenServerError::Callback))
tracing::error!("Error in callback: '{error:?}'");
(false, Err(GenServerError::Callback))
}
};
// Send response back
Expand All @@ -246,51 +237,49 @@ pub trait GenServer: Send + Sized + Clone {
"GenServer failed to send response back, client must have died"
)
};
(keep_running, new_state)
keep_running
}
Some(GenServerInMsg::Cast { message }) => {
match AssertUnwindSafe(self.handle_cast(message, handle))
.catch_unwind()
.await
{
Ok(response) => match response {
CastResponse::NoReply(new_state) => (true, new_state),
CastResponse::Stop => (false, state_clone),
CastResponse::NoReply => true,
CastResponse::Stop => false,
CastResponse::Unused => {
tracing::error!("GenServer received unexpected CastMessage");
(false, state_clone)
false
}
},
Err(error) => {
tracing::trace!(
"Error in callback, reverting state - Error: '{error:?}'"
);
(true, state_clone)
tracing::trace!("Error in callback: '{error:?}'");
false
}
}
}
None => {
// Channel has been closed; won't receive further messages. Stop the server.
(false, self)
false
}
};
Ok((new_state, keep_running))
keep_running
}
}

fn handle_call(
self,
&mut self,
_message: Self::CallMsg,
_handle: &GenServerHandle<Self>,
) -> impl Future<Output = CallResponse<Self>> + Send {
async { CallResponse::Unused }
}

fn handle_cast(
self,
&mut self,
_message: Self::CastMsg,
_handle: &GenServerHandle<Self>,
) -> impl Future<Output = CastResponse<Self>> + Send {
) -> impl Future<Output = CastResponse> + Send {
async { CastResponse::Unused }
}

Expand All @@ -316,7 +305,6 @@ mod tests {
time::Duration,
};

#[derive(Clone)]
struct BadlyBehavedTask;

#[derive(Clone)]
Expand All @@ -336,25 +324,24 @@ mod tests {
type Error = Unused;

async fn handle_call(
self,
&mut self,
_: Self::CallMsg,
_: &GenServerHandle<Self>,
) -> CallResponse<Self> {
CallResponse::Stop(Unused)
}

async fn handle_cast(
self,
&mut self,
_: Self::CastMsg,
_: &GenServerHandle<Self>,
) -> CastResponse<Self> {
) -> CastResponse {
rt::sleep(Duration::from_millis(20)).await;
thread::sleep(Duration::from_secs(2));
CastResponse::Stop
}
}

#[derive(Clone)]
struct WellBehavedTask {
pub count: u64,
}
Expand All @@ -366,28 +353,25 @@ mod tests {
type Error = Unused;

async fn handle_call(
self,
&mut self,
message: Self::CallMsg,
_: &GenServerHandle<Self>,
) -> CallResponse<Self> {
match message {
InMessage::GetCount => {
let count = self.count;
CallResponse::Reply(self, OutMsg::Count(count))
}
InMessage::GetCount => CallResponse::Reply(OutMsg::Count(self.count)),
InMessage::Stop => CallResponse::Stop(OutMsg::Count(self.count)),
}
}

async fn handle_cast(
mut self,
&mut self,
_: Self::CastMsg,
handle: &GenServerHandle<Self>,
) -> CastResponse<Self> {
) -> CastResponse {
self.count += 1;
println!("{:?}: good still alive", thread::current().id());
send_after(Duration::from_millis(100), handle.to_owned(), Unused);
CastResponse::NoReply(self)
CastResponse::NoReply
}
}

Expand Down Expand Up @@ -433,7 +417,7 @@ mod tests {

const TIMEOUT_DURATION: Duration = Duration::from_millis(100);

#[derive(Debug, Default, Clone)]
#[derive(Debug, Default)]
struct SomeTask;

#[derive(Clone)]
Expand All @@ -449,20 +433,20 @@ mod tests {
type Error = Unused;

async fn handle_call(
self,
&mut self,
message: Self::CallMsg,
_handle: &GenServerHandle<Self>,
) -> CallResponse<Self> {
match message {
SomeTaskCallMsg::SlowOperation => {
// Simulate a slow operation that will not resolve in time
rt::sleep(TIMEOUT_DURATION * 2).await;
CallResponse::Reply(self, Unused)
CallResponse::Reply(Unused)
}
SomeTaskCallMsg::FastOperation => {
// Simulate a fast operation that resolves in time
rt::sleep(TIMEOUT_DURATION / 2).await;
CallResponse::Reply(self, Unused)
CallResponse::Reply(Unused)
}
}
}
Expand All @@ -486,7 +470,6 @@ mod tests {
});
}

#[derive(Clone)]
struct SomeTaskThatFailsOnInit {
sender_channel: Arc<Mutex<mpsc::Receiver<u8>>>,
}
Expand Down
11 changes: 5 additions & 6 deletions concurrency/src/tasks/stream_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,6 @@ use crate::tasks::{

type SummatoryHandle = GenServerHandle<Summatory>;

#[derive(Clone)]
struct Summatory {
count: u16,
}
Expand Down Expand Up @@ -40,26 +39,26 @@ impl GenServer for Summatory {
type Error = ();

async fn handle_cast(
mut self,
&mut self,
message: Self::CastMsg,
_handle: &GenServerHandle<Self>,
) -> CastResponse<Self> {
) -> CastResponse {
match message {
SummatoryCastMessage::Add(val) => {
self.count += val;
CastResponse::NoReply(self)
CastResponse::NoReply
}
SummatoryCastMessage::Stop => CastResponse::Stop,
}
}

async fn handle_call(
self,
&mut self,
_message: Self::CallMsg,
_handle: &SummatoryHandle,
) -> CallResponse<Self> {
let current_value = self.count;
CallResponse::Reply(self, current_value)
CallResponse::Reply(current_value)
}
}

Expand Down
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