From eda876f2d752c3aa90c555e224da3080492e129e Mon Sep 17 00:00:00 2001
From: Alex Sharov <AskAlexSharov@gmail.com>
Date: Sat, 25 Feb 2023 18:02:01 +0700
Subject: [PATCH] cursors pool

---
 mdbx/cursor.go      |  37 +++++++++++--
 mdbx/cursor_test.go | 127 ++++++++++++++++++++++++++++++++++++++++----
 mdbx/error_unix.go  |   1 +
 3 files changed, 151 insertions(+), 14 deletions(-)

diff --git a/mdbx/cursor.go b/mdbx/cursor.go
index 4b9301d..02dcb7e 100644
--- a/mdbx/cursor.go
+++ b/mdbx/cursor.go
@@ -7,6 +7,8 @@ package mdbx
 */
 import "C"
 import (
+	"fmt"
+	"sync"
 	"unsafe"
 )
 
@@ -71,14 +73,24 @@ func openCursor(txn *Txn, db DBI) (*Cursor, error) {
 	return c, nil
 }
 
-// Renew associates readonly cursor with txn.
+// Renew associates cursor with txn.
 //
 // See mdb_cursor_renew.
 func (c *Cursor) Renew(txn *Txn) error {
 	ret := C.mdbx_cursor_renew(txn._txn, c._c)
-	err := operrno("mdbx_cursor_renew", ret)
-	if err != nil {
-		return err
+	if ret != success {
+		return operrno("mdbx_cursor_renew", ret)
+	}
+	c.txn = txn
+	return nil
+}
+
+// Bind Using of the `mdbx_cursor_bind()` is equivalent to calling mdbx_cursor_renew() but with specifying an arbitrary
+// dbi handle.
+func (c *Cursor) Bind(txn *Txn, db DBI) error {
+	ret := C.mdbx_cursor_bind(txn._txn, c._c, C.MDBX_dbi(db))
+	if ret != success {
+		return operrno("mdbx_cursor_bind", ret)
 	}
 	c.txn = txn
 	return nil
@@ -308,3 +320,20 @@ func (c *Cursor) Count() (uint64, error) {
 	}
 	return uint64(_size), nil
 }
+
+var cursorPool = sync.Pool{
+	New: func() interface{} {
+		return CreateCursor()
+	},
+}
+
+func CursorFromPool() *Cursor { return cursorPool.Get().(*Cursor) }
+func CursorToPool(c *Cursor)  { cursorPool.Put(c) }
+
+func CreateCursor() *Cursor {
+	c := &Cursor{_c: C.mdbx_cursor_create(nil)}
+	if c._c == nil {
+		panic(fmt.Errorf("mdbx.CreateCursor: OOM"))
+	}
+	return c
+}
diff --git a/mdbx/cursor_test.go b/mdbx/cursor_test.go
index 2caeb07..efeb240 100644
--- a/mdbx/cursor_test.go
+++ b/mdbx/cursor_test.go
@@ -886,6 +886,90 @@ func TestCursor_Renew(t *testing.T) {
 	}
 }
 
+func TestCursor_Bind(t *testing.T) {
+	env := setup(t)
+
+	var db1, db2 DBI
+	err := env.Update(func(txn *Txn) (err error) {
+		db1, err = txn.CreateDBI("testing1")
+		return err
+	})
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	err = env.Update(func(txn *Txn) (err error) {
+		put := func(k, v string) {
+			if err == nil {
+				err = txn.Put(db1, []byte(k), []byte(v), 0)
+			}
+		}
+		put("k1", "v1")
+		put("k2", "v2")
+		put("k3", "v3")
+		return err
+	})
+	if err != nil {
+		t.Error("err")
+	}
+
+	var cur *Cursor
+	err = env.View(func(txn *Txn) (err error) {
+		cur, err = txn.OpenCursor(db2)
+		if err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		t.Error(err)
+	}
+
+	err = env.View(func(txn *Txn) (err error) {
+		{
+			err = cur.Bind(txn, db1)
+			if err != nil {
+				return err
+			}
+
+			k, v, err := cur.Get(nil, nil, Next)
+			if err != nil {
+				return err
+			}
+			if string(k) != "k1" {
+				return fmt.Errorf("key: %q", k)
+			}
+			if string(v) != "v1" {
+				return fmt.Errorf("val: %q", v)
+			}
+		}
+
+		{
+			c2 := CreateCursor()
+			err = c2.Bind(txn, db1)
+			if err != nil {
+				return err
+			}
+
+			k, v, err := c2.Get(nil, nil, Next)
+			if err != nil {
+				return err
+			}
+			if string(k) != "k1" {
+				return fmt.Errorf("key: %q", k)
+			}
+			if string(v) != "v1" {
+				return fmt.Errorf("val: %q", v)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Error(err)
+	}
+}
+
 func BenchmarkCursor(b *testing.B) {
 	env := setup(b)
 
@@ -924,9 +1008,10 @@ func BenchmarkCursor(b *testing.B) {
 func BenchmarkCursor_Renew(b *testing.B) {
 	env := setup(b)
 
+	var db DBI
 	var cur *Cursor
 	err := env.View(func(txn *Txn) (err error) {
-		db, err := txn.OpenRoot(0)
+		db, err = txn.OpenRoot(0)
 		if err != nil {
 			return err
 		}
@@ -939,16 +1024,38 @@ func BenchmarkCursor_Renew(b *testing.B) {
 	}
 
 	_ = env.View(func(txn *Txn) (err error) {
-		b.ResetTimer()
-		defer b.StopTimer()
-
-		for i := 0; i < b.N; i++ {
-			err = cur.Renew(txn)
-			if err != nil {
-				return err
+		b.Run("1", func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				if err := cur.Renew(txn); err != nil {
+					panic(err)
+				}
 			}
-		}
-
+		})
+		b.Run("2", func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				if err := cur.Bind(txn, db); err != nil {
+					panic(err)
+				}
+			}
+		})
+		b.Run("3", func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				c, err := txn.OpenCursor(db)
+				if err != nil {
+					panic(err)
+				}
+				c.Close()
+			}
+		})
+		b.Run("4", func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				cur := CursorFromPool()
+				if err := cur.Bind(txn, db); err != nil {
+					panic(err)
+				}
+				CursorToPool(cur)
+			}
+		})
 		return nil
 	})
 }
diff --git a/mdbx/error_unix.go b/mdbx/error_unix.go
index 71c57b1..9981ed7 100644
--- a/mdbx/error_unix.go
+++ b/mdbx/error_unix.go
@@ -1,3 +1,4 @@
+//go:build !windows
 // +build !windows
 
 package mdbx