keep track when fsync is called

simulator/runner/file.rs

@@ -31,6 +31,8 @@ pub(crate) struct SimulatorFile {
     pub(crate) rng: RefCell<ChaCha8Rng>,
 
     pub latency_probability: usize,
+
+    pub sync_completion: RefCell<Option<Arc<limbo_core::Completion>>>,
 }
 
 unsafe impl Send for SimulatorFile {}
@@ -185,7 +187,9 @@ impl File for SimulatorFile {
             };
             sync_completion.complete = Box::new(new_complete);
         };
-        self.inner.sync(c)
+        let c = self.inner.sync(c)?;
+        *self.sync_completion.borrow_mut() = Some(c.clone());
+        Ok(c)
     }
 
     fn size(&self) -> Result<u64> {

simulator/runner/io.rs

@@ -85,6 +85,7 @@ impl IO for SimulatorIO {
             page_size: self.page_size,
             rng: RefCell::new(ChaCha8Rng::seed_from_u64(self.seed)),
             latency_probability: self.latency_probability,
+            sync_completion: RefCell::new(None),
         });
         self.files.borrow_mut().push(file.clone());
         Ok(file)