From ff08c9690e6be8161032fa94a174646ef211dfb9 Mon Sep 17 00:00:00 2001
From: Roman Atachiants <roman.atachiants@gmail.com>
Date: Mon, 13 Jun 2022 00:50:02 +0400
Subject: [PATCH] Fix snapshot race (#69)

---
 snapshot.go | 12 ++++++++++++
 txn_lock.go | 17 -----------------
 2 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/snapshot.go b/snapshot.go
index 18d2505..ce4b4a0 100644
--- a/snapshot.go
+++ b/snapshot.go
@@ -218,3 +218,15 @@ func (c *Collection) chunks() int {
 	max, _ := c.fill.Max()
 	return int(commit.ChunkAt(max) + 1)
 }
+
+// readChunk acquires appropriate locks for a chunk and executes a read callback.
+// This is used for snapshotting purposes only.
+func (c *Collection) readChunk(chunk commit.Chunk, fn func(uint64, commit.Chunk, bitmap.Bitmap) error) error {
+
+	// Lock both the chunk and the fill list
+	c.slock.RLock(uint(chunk))
+	c.lock.RLock()
+	defer c.slock.RUnlock(uint(chunk))
+	defer c.lock.RUnlock()
+	return fn(c.commits[chunk], chunk, chunk.OfBitmap(c.fill))
+}
diff --git a/txn_lock.go b/txn_lock.go
index 2ca206b..d2db367 100644
--- a/txn_lock.go
+++ b/txn_lock.go
@@ -93,20 +93,3 @@ func (txn *Txn) rangeWrite(fn func(commitID uint64, chunk commit.Chunk, fill bit
 		lock.Unlock(uint(chunk))
 	})
 }
-
-// readChunk acquires appropriate locks for a chunk and executes a read callback
-func (c *Collection) readChunk(chunk commit.Chunk, fn func(uint64, commit.Chunk, bitmap.Bitmap) error) (err error) {
-	lock := c.slock
-	lock.RLock(uint(chunk))
-
-	// Compute the fill
-	c.lock.RLock()
-	fill := chunk.OfBitmap(c.fill)
-	commitID := c.commits[chunk]
-	c.lock.RUnlock()
-
-	// Call the delegate
-	err = fn(commitID, chunk, fill)
-	lock.RUnlock(uint(chunk))
-	return
-}