Latest DeliveryPolicy

Cargo.toml

@@ -27,7 +27,7 @@ oneshot = { version = "0.1.6", default-features = false, features = ["std"] }
 parking_lot = "0.12.1"
 pin-project = "1.1.5"
 rmodbus = { version = "0.9.3" }
-roboplc-derive = { version = "0.1.3" }
+roboplc-derive = { version = "0.1.4" }
 serde = { version = "1.0.197", features = ["derive", "rc"] }
 serial = "0.4.0"
 sysinfo = "0.30.6"

README.md

@@ -61,6 +61,8 @@ channels.
 Data policies supported:
 
 * **Always** a frame is always delivered
+* **Latest** a frame is always delivered, previous are dropped if no room
+  (acts like a ring-buffer)
 * **Optional** a frame can be skipped if no room
 * **Single** a frame must be delivered only once (the latest one)
 * **SingleOptional** a frame must be delivered only once (the latest one) and

src/lib.rs

@@ -116,6 +116,9 @@ impl Error {
     pub fn invalid_data<S: fmt::Display>(msg: S) -> Self {
         Error::InvalidData(msg.to_string())
     }
+    pub fn io<S: fmt::Display>(msg: S) -> Self {
+        Error::IO(msg.to_string())
+    }
 }
 
 /// Data delivery policies, used by [`hub::Hub`], [`pchannel::Receiver`] and [`pdeque::Deque`]
@@ -124,6 +127,8 @@ pub enum DeliveryPolicy {
     #[default]
     /// always deliver, fail if no room (default)
     Always,
+    /// always deliver, drop the previous if no room (act as a ring-buffer)
+    Latest,
     /// skip delivery if no room
     Optional,
     /// always deliver the frame but always in a single copy (latest)
@@ -153,6 +158,7 @@ impl fmt::Display for DeliveryPolicy {
             "{}",
             match self {
                 DeliveryPolicy::Always => "always",
+                DeliveryPolicy::Latest => "latest",
                 DeliveryPolicy::Optional => "optional",
                 DeliveryPolicy::Single => "single",
                 DeliveryPolicy::SingleOptional => "single-optional",

src/pdeque.rs

@@ -68,6 +68,18 @@ where
         if value.is_delivery_policy_single() {
             self.data.retain(|d| !d.eq_kind(&value) && !d.is_expired());
         }
+        macro_rules! push_final {
+            () => {
+                if self.data.len() < self.capacity {
+                    push!()
+                } else {
+                    TryPushOutput {
+                        pushed: false,
+                        value: Some(value),
+                    }
+                }
+            };
+        }
         if self.data.len() < self.capacity {
             push!()
         } else {
@@ -84,14 +96,24 @@ where
                             true
                         }
                     });
-                    if self.data.len() < self.capacity {
-                        push!()
-                    } else {
-                        TryPushOutput {
-                            pushed: false,
-                            value: Some(value),
+                    push_final!()
+                }
+                DeliveryPolicy::Latest => {
+                    let mut entry_removed = false;
+                    self.data.retain(|d| {
+                        if entry_removed {
+                            true
+                        } else if d.is_expired()
+                            || d.is_delivery_policy_optional()
+                            || d.eq_kind(&value)
+                        {
+                            entry_removed = true;
+                            false
+                        } else {
+                            true
                         }
-                    }
+                    });
+                    push_final!()
                 }
                 DeliveryPolicy::Optional | DeliveryPolicy::SingleOptional => TryPushOutput {
                     pushed: false,