From c6724ca71fc35fd8f23c62204a227ef573236a1a Mon Sep 17 00:00:00 2001
From: Dev Ojha <ValarDragon@users.noreply.github.com>
Date: Sun, 10 Oct 2021 06:03:34 -0500
Subject: [PATCH] Add an option to create MemDB iterators with no Mutex for the
 CacheKVStore (#187)

* Add an option to create MemDB iterators with no Mutex for the CacheKVStore

* Update changelog
---
 .gitignore        |  3 ++-
 CHANGELOG.md      |  4 ++++
 memdb.go          | 16 ++++++++++++++++
 memdb_iterator.go | 14 ++++++++++++--
 4 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/.gitignore b/.gitignore
index b3efc3918..ce205f69a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,4 +11,5 @@
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
 
-.idea
\ No newline at end of file
+.idea
+vendor/*
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f667baa6..cb43176ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## Pending
+
+* Add an option for creating a mem db with no mutex
+
 ## 0.6.4
 
 **2021-02-09**
diff --git a/memdb.go b/memdb.go
index 604e6a06e..d019af230 100644
--- a/memdb.go
+++ b/memdb.go
@@ -190,3 +190,19 @@ func (db *MemDB) ReverseIterator(start, end []byte) (Iterator, error) {
 	}
 	return newMemDBIterator(db, start, end, true), nil
 }
+
+// IteratorNoMtx makes an iterator with no mutex.
+func (db *MemDB) IteratorNoMtx(start, end []byte) (Iterator, error) {
+	if (start != nil && len(start) == 0) || (end != nil && len(end) == 0) {
+		return nil, errKeyEmpty
+	}
+	return newMemDBIteratorMtxChoice(db, start, end, false, false), nil
+}
+
+// ReverseIteratorNoMtx makes an iterator with no mutex.
+func (db *MemDB) ReverseIteratorNoMtx(start, end []byte) (Iterator, error) {
+	if (start != nil && len(start) == 0) || (end != nil && len(end) == 0) {
+		return nil, errKeyEmpty
+	}
+	return newMemDBIteratorMtxChoice(db, start, end, true, false), nil
+}
diff --git a/memdb_iterator.go b/memdb_iterator.go
index 2a61e3757..ebd104f67 100644
--- a/memdb_iterator.go
+++ b/memdb_iterator.go
@@ -21,12 +21,17 @@ type memDBIterator struct {
 	item   *item
 	start  []byte
 	end    []byte
+	useMtx bool
 }
 
 var _ Iterator = (*memDBIterator)(nil)
 
 // newMemDBIterator creates a new memDBIterator.
 func newMemDBIterator(db *MemDB, start []byte, end []byte, reverse bool) *memDBIterator {
+	return newMemDBIteratorMtxChoice(db, start, end, reverse, true)
+}
+
+func newMemDBIteratorMtxChoice(db *MemDB, start []byte, end []byte, reverse bool, useMtx bool) *memDBIterator {
 	ctx, cancel := context.WithCancel(context.Background())
 	ch := make(chan *item, chBufferSize)
 	iter := &memDBIterator{
@@ -34,11 +39,16 @@ func newMemDBIterator(db *MemDB, start []byte, end []byte, reverse bool) *memDBI
 		cancel: cancel,
 		start:  start,
 		end:    end,
+		useMtx: useMtx,
 	}
 
-	db.mtx.RLock()
+	if useMtx {
+		db.mtx.RLock()
+	}
 	go func() {
-		defer db.mtx.RUnlock()
+		if useMtx {
+			defer db.mtx.RUnlock()
+		}
 		// Because we use [start, end) for reverse ranges, while btree uses (start, end], we need
 		// the following variables to handle some reverse iteration conditions ourselves.
 		var (