checkin part 2 solution

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/bin/compaction-simulator.rs

@@ -343,6 +343,7 @@ fn main() {
                 } else {
                     storage.dump_original_id(false, false);
                 }
+                println!("--- Compaction Task ---");
                 let mut num_compactions = 0;
                 while let Some(task) = {
                     println!("--- Compaction Task ---");

mini-lsm-starter/src/bin/mini-lsm-cli.rs

@@ -107,6 +107,19 @@ fn main() -> Result<()> {
             } else {
                 println!("{} not exist", key);
             }
+        } else if line == "scan" {
+            let mut iter = lsm.scan(std::ops::Bound::Unbounded, std::ops::Bound::Unbounded)?;
+            let mut cnt = 0;
+            while iter.is_valid() {
+                println!(
+                    "{:?}={:?}",
+                    Bytes::copy_from_slice(iter.key()),
+                    Bytes::copy_from_slice(iter.value()),
+                );
+                iter.next()?;
+                cnt += 1;
+            }
+            println!("{} keys scanned", cnt);
         } else if line.starts_with("scan ") {
             let Some((_, rest)) = line.split_once(' ') else {
                 println!("invalid command");
@@ -137,7 +150,7 @@ fn main() -> Result<()> {
             lsm.force_flush()?;
         } else if line == "full_compaction" {
             lsm.force_full_compaction()?;
-        } else if line == "quit" {
+        } else if line == "quit" || line == "close" {
             lsm.close()?;
             break;
         } else {

mini-lsm-starter/src/lsm_storage.rs

@@ -166,10 +166,16 @@ impl MiniLsm {
         self.inner.scan(lower, upper)
     }
 
+    /// Only call this in test cases due to race conditions
     pub fn force_flush(&self) -> Result<()> {
-        self.inner
-            .force_freeze_memtable(&self.inner.state_lock.lock())?;
-        self.inner.force_flush_next_imm_memtable()
+        if !self.inner.state.read().memtable.is_empty() {
+            self.inner
+                .force_freeze_memtable(&self.inner.state_lock.lock())?;
+        }
+        if !self.inner.state.read().imm_memtables.is_empty() {
+            self.inner.force_flush_next_imm_memtable()?;
+        }
+        Ok(())
     }
 
     pub fn force_full_compaction(&self) -> Result<()> {
@@ -247,7 +253,7 @@ impl LsmStorageInner {
         Self::path_of_wal_static(&self.path, id)
     }
 
-    fn sync_dir(&self) -> Result<()> {
+    pub(super) fn sync_dir(&self) -> Result<()> {
         unimplemented!()
     }
 

mini-lsm-starter/src/mem_table.rs

@@ -88,6 +88,11 @@ impl MemTable {
         self.approximate_size
             .load(std::sync::atomic::Ordering::Relaxed)
     }
+
+    /// Only use this function when closing the database
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
 }
 
 type SkipMapRangeIter<'a> =