From ea61c390e69524ecff701a8b0f9c812978717463 Mon Sep 17 00:00:00 2001
From: Evgeny Fomin <fominok@hotmail.com>
Date: Tue, 5 Nov 2024 18:49:37 +0100
Subject: [PATCH] wip

---
 grovedb/src/merk_cache.rs | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/grovedb/src/merk_cache.rs b/grovedb/src/merk_cache.rs
index 7804fad3..31219ee0 100644
--- a/grovedb/src/merk_cache.rs
+++ b/grovedb/src/merk_cache.rs
@@ -30,25 +30,24 @@ struct CachedMerk<'db> {
 /// structure. Eventually we'll have enough info at the same place to perform
 /// necessary propagations as well.
 pub(crate) struct MerkCache<'db, 'b, B> {
+    merks: BTreeMap<SubtreePath<'b, B>, CachedMerk<'db>>,
     db: &'db GroveDb,
     tx: &'db Transaction<'db>,
-    batch: &'db StorageBatch,
+    batch: &'static StorageBatch,
     version: &'db GroveVersion,
-    merks: BTreeMap<SubtreePath<'b, B>, CachedMerk<'db>>,
 }
 
 impl<'db, 'b, B: AsRef<[u8]>> MerkCache<'db, 'b, B> {
     pub(crate) fn new(
         db: &'db GroveDb,
         tx: &'db Transaction<'db>,
-        batch: &'db StorageBatch,
         version: &'db GroveVersion,
     ) -> Self {
         MerkCache {
             db,
             tx,
-            batch,
             version,
+            batch: Box::leak(Box::new(StorageBatch::default())),
             merks: Default::default(),
         }
     }
@@ -131,6 +130,19 @@ impl<'db, 'b, B: AsRef<[u8]>> MerkCache<'db, 'b, B> {
 
         Ok(result).wrap_with_cost(cost)
     }
+
+    /// Summarizes all performed operations on this `MerkCache` with necessary
+    /// propagations into a `Storagebatch`.
+    pub(crate) fn finalize(self) -> Box<StorageBatch> {
+        let batch_ptr = self.batch as *const _;
+        // Remove all possible usages of the `StorageBatch`:
+        drop(self);
+
+        // SAFETY: The batch reference was created by `Box::leak` and restored into a
+        // `Box` form. No shared usage of that memory exists because the
+        // `MerkCache` structure was dropped above.
+        unsafe { Box::from_raw(batch_ptr as *mut _) }
+    }
 }
 
 /// Handle to a cached Merk.
@@ -193,7 +205,7 @@ mod tests {
         let db = make_deep_tree(&version);
         let tx = db.start_transaction();
         let batch = StorageBatch::new();
-        let mut cache = MerkCache::new(&db, &tx, &batch, version);
+        let mut cache = MerkCache::new(&db, &tx, version);
 
         let mut cost: OperationCost = Default::default();
         let [test1, test2] = cache
@@ -231,7 +243,7 @@ mod tests {
         let db = make_deep_tree(&version);
         let tx = db.start_transaction();
         let batch = StorageBatch::new();
-        let mut cache = MerkCache::new(&db, &tx, &batch, version);
+        let mut cache = MerkCache::new(&db, &tx, version);
 
         let _ = cache.get_multi_mut([
             SubtreePath::from(&[TEST_LEAF]),