Example with periodic task (#28)

Author: slinkydeveloper

examples/cron.rs

@@ -0,0 +1,90 @@
+use restate_sdk::prelude::*;
+use std::time::Duration;
+
+/// This example shows how to implement a periodic task, by invoking itself in a loop.
+///
+/// The `start()` handler schedules the first call to `run()`, and then each `run()` will re-schedule itself.
+///
+/// To "break" the loop, we use a flag we persist in state, which is removed when `stop()` is invoked.
+/// Its presence determines whether the task is active or not.
+///
+/// To start it:
+///
+/// ```shell
+/// $ curl -v http://localhost:8080/PeriodicTask/my-periodic-task/start
+/// ```
+#[restate_sdk::object]
+trait PeriodicTask {
+    /// Schedules the periodic task to start
+    async fn start() -> Result<(), TerminalError>;
+    /// Stops the periodic task
+    async fn stop() -> Result<(), TerminalError>;
+    /// Business logic of the periodic task
+    async fn run() -> Result<(), TerminalError>;
+}
+
+struct PeriodicTaskImpl;
+
+const ACTIVE: &str = "active";
+
+impl PeriodicTask for PeriodicTaskImpl {
+    async fn start(&self, context: ObjectContext<'_>) -> Result<(), TerminalError> {
+        if context
+            .get::<bool>(ACTIVE)
+            .await?
+            .is_some_and(|enabled| enabled)
+        {
+            // If it's already activated, just do nothing
+            return Ok(());
+        }
+
+        // Schedule the periodic task
+        PeriodicTaskImpl::schedule_next(&context);
+
+        // Mark the periodic task as active
+        context.set(ACTIVE, true);
+
+        Ok(())
+    }
+
+    async fn stop(&self, context: ObjectContext<'_>) -> Result<(), TerminalError> {
+        // Remove the active flag
+        context.clear(ACTIVE);
+
+        Ok(())
+    }
+
+    async fn run(&self, context: ObjectContext<'_>) -> Result<(), TerminalError> {
+        if context.get::<bool>(ACTIVE).await?.is_none() {
+            // Task is inactive, do nothing
+            return Ok(());
+        }
+
+        // --- Periodic task business logic!
+        println!("Triggered the periodic task!");
+
+        // Schedule the periodic task
+        PeriodicTaskImpl::schedule_next(&context);
+
+        Ok(())
+    }
+}
+
+impl PeriodicTaskImpl {
+    fn schedule_next(context: &ObjectContext<'_>) {
+        // To schedule, create a client to the callee handler (in this case, we're calling ourselves)
+        context
+            .object_client::<PeriodicTaskClient>(context.key())
+            .run()
+            // And send with a delay
+            .send_with_delay(Duration::from_secs(10));
+    }
+}
+
+#[tokio::main]
+async fn main() {
+    tracing_subscriber::fmt::init();
+    HttpServer::new(Endpoint::builder().bind(PeriodicTaskImpl.serve()).build())
+        .listen_and_serve("0.0.0.0:9080".parse().unwrap())
+        .await;
+}