feat(core): the restarting policy can be overridden via configuration…

… for each actor.

`RestartParams` have been added for `RestartPolicy::always(..)` and `RestartPolicy::on_failure(..)`. The linear backoff has been replaced with an exponential approach, with a configurable limit for restarts.

BREAKING CHANGE: The default RestartPolicy is set to `RestartPolicy::never()`.

elfo-configurer/src/lib.rs

@@ -22,7 +22,7 @@ use elfo_core::{
     },
     msg, scope,
     signal::{Signal, SignalKind},
-    ActorGroup, ActorStatus, Addr, Blueprint, Context, Topology,
+    ActorGroup, ActorStatus, Addr, Blueprint, Context, RestartParams, RestartPolicy, Topology,
 };
 
 pub use self::protocol::*;
@@ -48,6 +48,10 @@ fn blueprint(topology: &Topology, source: ConfigSource) -> Blueprint {
     let topology = topology.clone();
     ActorGroup::new()
         .stop_order(100)
+        .restart_policy(RestartPolicy::on_failure(RestartParams::new(
+            Duration::from_secs(5),
+            Duration::from_secs(30),
+        )))
         .exec(move |ctx| Configurer::new(ctx, topology.clone(), source.clone()).main())
 }
 

elfo-core/Cargo.toml

@@ -50,6 +50,7 @@ regex = "1.6.0"
 thread_local = { version = "1.1.3", optional = true }
 unicycle = "0.9.3"
 rmp-serde = { version = "1.1.0", optional = true }
+humantime-serde = "1"
 
 [dev-dependencies]
 elfo-utils = { version = "0.2.3", path = "../elfo-utils", features = ["test-util"] }

elfo-core/src/actor.rs

@@ -9,11 +9,12 @@ use tracing::{error, info, warn};
 use crate::{
     envelope::Envelope,
     errors::{SendError, TrySendError},
-    group::{RestartPolicy, TerminationPolicy},
+    group::TerminationPolicy,
     mailbox::{Mailbox, RecvResult},
     messages::{ActorStatusReport, Terminate},
     msg,
     request_table::RequestTable,
+    restarting::RestartPolicy,
     scope,
     subscription::SubscriptionManager,
     Addr,
@@ -117,6 +118,62 @@ impl ActorStatusKind {
     }
 }
 
+// === ActorStartInfo ===
+
+/// A struct holding information related to an actor start.
+#[derive(Debug, Clone)]
+#[non_exhaustive]
+pub struct ActorStartInfo {
+    /// The cause for the actor start, indicating why the actor is being
+    /// initialized.
+    pub cause: ActorStartCause,
+}
+
+/// An enum representing various causes for an actor to start.
+#[derive(Debug, Clone)]
+#[non_exhaustive]
+pub enum ActorStartCause {
+    /// The actor started because its group was mounted.
+    GroupMounted,
+    /// The actor started in response to a message.
+    OnMessage,
+    /// The actor started due to the restart policy.
+    Restarted,
+}
+
+impl ActorStartInfo {
+    pub(crate) fn on_group_mounted() -> Self {
+        Self {
+            cause: ActorStartCause::GroupMounted,
+        }
+    }
+
+    pub(crate) fn on_message() -> Self {
+        Self {
+            cause: ActorStartCause::OnMessage,
+        }
+    }
+
+    pub(crate) fn on_restart() -> Self {
+        Self {
+            cause: ActorStartCause::Restarted,
+        }
+    }
+}
+
+impl ActorStartCause {
+    pub fn is_group_mounted(&self) -> bool {
+        matches!(self, ActorStartCause::GroupMounted)
+    }
+    pub fn is_restarted(&self) -> bool {
+        matches!(self, ActorStartCause::Restarted)
+    }
+
+    pub fn is_on_message(&self) -> bool {
+        matches!(self, ActorStartCause::OnMessage)
+    }
+}
+
 // === Actor ===
 
 pub(crate) struct Actor {
@@ -127,6 +184,7 @@ pub(crate) struct Actor {
     control: RwLock<ControlBlock>,
     finished: ManualResetEvent, // TODO: remove in favor of `status_subscription`?
     status_subscription: Arc<SubscriptionManager>,
+    start_info: ActorStartInfo,
 }
 
 struct ControlBlock {
@@ -139,6 +197,7 @@ impl Actor {
     pub(crate) fn new(
         meta: Arc<ActorMeta>,
         addr: Addr,
+        start_info: ActorStartInfo,
         termination_policy: TerminationPolicy,
         status_subscription: Arc<SubscriptionManager>,
     ) -> Self {
@@ -153,6 +212,7 @@ impl Actor {
             }),
             finished: ManualResetEvent::new(false),
             status_subscription,
+            start_info,
         }
     }
 
@@ -209,6 +269,10 @@ impl Actor {
         &self.request_table
     }
 
+    pub(crate) fn start_info(&self) -> ActorStartInfo {
+        self.start_info.clone()
+    }
+
     pub(crate) fn restart_policy(&self) -> Option<RestartPolicy> {
         self.control.read().restart_policy.clone()
     }

elfo-core/src/config.rs

@@ -162,6 +162,7 @@ pub(crate) struct SystemConfig {
     pub(crate) logging: crate::logging::LoggingConfig,
     pub(crate) dumping: crate::dumping::DumpingConfig,
     pub(crate) telemetry: crate::telemetry::TelemetryConfig,
+    pub(crate) restarting: crate::restarting::RestartingConfig,
 }
 
 // === Secret ===

elfo-core/src/context.rs

@@ -7,20 +7,20 @@ use tracing::{info, trace};
 use elfo_utils::unlikely;
 
 use crate::{
-    actor::{Actor, ActorStatus},
+    actor::{Actor, ActorStartInfo, ActorStatus},
     addr::Addr,
     address_book::AddressBook,
     config::AnyConfig,
     demux::Demux,
     dumping::{Direction, Dump, Dumper, INTERNAL_CLASS},
     envelope::{AnyMessageBorrowed, AnyMessageOwned, Envelope, EnvelopeOwned, MessageKind},
     errors::{RequestError, SendError, TryRecvError, TrySendError},
-    group::RestartPolicy,
     mailbox::RecvResult,
     message::{Message, Request},
     messages, msg,
     object::ObjectArc,
     request_table::ResponseToken,
+    restarting::RestartPolicy,
     routers::Singleton,
     scope,
     source::{SourceHandle, Sources, UnattachedSource},
@@ -624,6 +624,41 @@ impl<C, K> Context<C, K> {
         }
     }
 
+    /// Retrieves information related to the start of the actor.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if the context is pruned, indicating that the
+    /// required information is no longer available.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use elfo_core as elfo;
+    /// # use elfo_core::{ActorStartCause, ActorStartInfo};
+    /// # async fn exec(mut ctx: elfo::Context) {
+    /// match ctx.start_info().cause {
+    ///     ActorStartCause::GroupMounted => {
+    ///         // The actor started because its group was mounted.
+    ///     }
+    ///     ActorStartCause::OnMessage => {
+    ///         // The actor started in response to a message.
+    ///     }
+    ///     ActorStartCause::Restarted => {
+    ///         // The actor started due to the restart policy.
+    ///     }
+    ///     _ => {}
+    /// }
+    /// # }
+    /// ```
+    pub fn start_info(&self) -> ActorStartInfo {
+        self.actor
+            .as_ref()
+            .and_then(|o| o.as_actor())
+            .map(|a| a.start_info())
+            .expect("pruned context is not supported")
+    }
+
     fn pre_recv(&mut self) {
         self.stats.on_recv();
 

elfo-core/src/group.rs

@@ -8,6 +8,7 @@ use crate::{
     envelope::Envelope,
     exec::{Exec, ExecResult},
     object::{GroupHandle, GroupVisitor, Object},
+    restarting::RestartPolicy,
     routers::Router,
     runtime::RuntimeManager,
     supervisor::Supervisor,
@@ -47,13 +48,15 @@ impl<R, C> ActorGroup<R, C> {
     }
 
     /// The behaviour on actor termination.
-    /// `RestartPolicy::on_failures` is used by default.
+    ///
+    /// `RestartPolicy::never` is used by default.
     pub fn restart_policy(mut self, policy: RestartPolicy) -> Self {
         self.restart_policy = policy;
         self
     }
 
     /// The behaviour on the `Terminate` message.
+    ///
     /// `TerminationPolicy::closing` is used by default.
     pub fn termination_policy(mut self, policy: TerminationPolicy) -> Self {
         self.termination_policy = policy;
@@ -183,42 +186,3 @@ impl TerminationPolicy {
 
     // TODO: add `stop_spawning`?
 }
-
-/// The behaviour on actor termination.
-#[derive(Debug, Clone)]
-pub struct RestartPolicy {
-    pub(crate) mode: RestartMode,
-}
-
-impl Default for RestartPolicy {
-    fn default() -> Self {
-        Self::on_failures()
-    }
-}
-
-#[derive(Debug, Clone)]
-pub(crate) enum RestartMode {
-    Always,
-    OnFailures,
-    Never,
-}
-
-impl RestartPolicy {
-    pub fn always() -> Self {
-        Self {
-            mode: RestartMode::Always,
-        }
-    }
-
-    pub fn on_failures() -> Self {
-        Self {
-            mode: RestartMode::OnFailures,
-        }
-    }
-
-    pub fn never() -> Self {
-        Self {
-            mode: RestartMode::Never,
-        }
-    }
-}

elfo-core/src/init.rs

@@ -13,7 +13,7 @@ use elfo_utils::time::Instant;
 use crate::{memory_tracker::MemoryTracker, time::Interval};
 
 use crate::{
-    actor::{Actor, ActorMeta, ActorStatus},
+    actor::{Actor, ActorMeta, ActorStartInfo, ActorStatus},
     addr::{Addr, GroupNo},
     config::SystemConfig,
     context::Context,
@@ -173,6 +173,7 @@ pub async fn do_start<F: Future>(
     let actor = Actor::new(
         meta.clone(),
         addr,
+        ActorStartInfo::on_group_mounted(),
         Default::default(),
         Arc::new(SubscriptionManager::new(ctx.clone())),
     );

elfo-core/src/lib.rs

@@ -11,15 +11,16 @@ extern crate self as elfo_core;
 
 // TODO: revise this list
 pub use crate::{
-    actor::{ActorMeta, ActorStatus, ActorStatusKind},
+    actor::{ActorMeta, ActorStartCause, ActorStartInfo, ActorStatus, ActorStatusKind},
     addr::Addr,
     config::Config,
     context::{Context, RequestBuilder},
     envelope::Envelope,
-    group::{ActorGroup, Blueprint, RestartPolicy, TerminationPolicy},
+    group::{ActorGroup, Blueprint, TerminationPolicy},
     local::{Local, MoveOwnership},
     message::{Message, Request},
     request_table::ResponseToken,
+    restarting::{RestartParams, RestartPolicy},
     source::{SourceHandle, UnattachedSource},
     topology::Topology,
 };
@@ -65,6 +66,7 @@ pub mod remote;
 #[cfg(all(feature = "network", not(feature = "unstable")))]
 mod remote;
 mod request_table;
+mod restarting;
 mod runtime;
 mod source;
 mod subscription;

elfo-core/src/node.rs

@@ -19,6 +19,7 @@ impl From<u16> for NodeNo {
 
 static NODE_NO: AtomicU16 = AtomicU16::new(0);
 
+#[stability::unstable]
 /// Returns the current `node_no`.
 pub fn node_no() -> Option<crate::addr::NodeNo> {
     crate::addr::NodeNo::from_bits(NODE_NO.load(Ordering::Relaxed))