fix(sim): Make simulation process actually continuous

crates/sim/src/task.rs

@@ -1,13 +1,17 @@
 use crate::{env::SimEnv, BuiltBlock, SharedSimEnv, SimCache, SimDb};
 use signet_types::constants::SignetSystemConstants;
-use tokio::select;
+use std::time::Duration;
+use tokio::{select, time::Instant};
 use tracing::{debug, info_span, trace, Instrument};
 use trevm::{
     helpers::Ctx,
     revm::{inspector::NoOpInspector, DatabaseRef, Inspector},
     Block, Cfg,
 };
 
+/// The amount of time to sleep between simulation rounds when there are no items to simulate.
+pub(crate) const SIM_SLEEP_MS: u64 = 50;
+
 /// Builds a single block by repeatedly invoking [`SimEnv`].
 #[derive(Debug)]
 pub struct BlockBuild<Db, Insp = NoOpInspector> {
@@ -76,9 +80,29 @@ where
         loop {
             let span = info_span!("build", round = i);
             let finish_by = self.finish_by.into();
+
+            let next_round_time = Instant::now() + Duration::from_millis(SIM_SLEEP_MS);
+
+            // If the next round time is past the deadline, we stop the simulation loop.
+            // This will stop the simulation even if there are items, but that is an acceptable tradeoff
+            // as we must ensure there's enough time to submit the blob to the host chain.
+            if next_round_time >= finish_by {
+                debug!("Next round time is past the deadline, stopping sim loop");
+                break;
+            }
+
+            // Only simulate if there are items to simulate.
+            // If there are not items, we sleep for [`SIM_SLEEP_MS`] and restart the loop.
+            if self.env.sim_items().is_empty() {
+                tokio::time::sleep_until(next_round_time).await;
+                continue;
+            }
+
+            // If there are items to simulate, we run a simulation round.
             let fut = self.round().instrument(span);
 
             select! {
+                biased;
                 _ = tokio::time::sleep_until(finish_by) => {
                     debug!("Deadline reached, stopping sim loop");
                     break;
@@ -87,10 +111,6 @@ where
                     i+= 1;
                     let remaining = self.env.sim_items().len();
                     trace!(%remaining, round = i, "Round completed");
-                    if remaining == 0 {
-                        debug!("No more items to simulate, stopping sim loop");
-                        break;
-                    }
                 }
             }
         }