From 4e4c7eb9749a58f4a61dae5cbb4c4cf410f9dcaa Mon Sep 17 00:00:00 2001
From: Daniel Smith <dbsmith@google.com>
Date: Fri, 16 Aug 2019 16:48:26 -0700
Subject: [PATCH] memory pools for walkers

---
 typed/typed.go    | 39 ++++++++++++++++++++++++++++++---------
 typed/validate.go | 26 +++++++++++++++++++++-----
 2 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/typed/typed.go b/typed/typed.go
index 6eaab261..3fbc4a99 100644
--- a/typed/typed.go
+++ b/typed/typed.go
@@ -18,6 +18,7 @@ package typed
 
 import (
 	"fmt"
+	"sync"
 
 	"sigs.k8s.io/structured-merge-diff/fieldpath"
 	"sigs.k8s.io/structured-merge-diff/schema"
@@ -66,7 +67,9 @@ func (tv TypedValue) AsValue() *value.Value {
 
 // Validate returns an error with a list of every spec violation.
 func (tv TypedValue) Validate() error {
-	if errs := tv.walker().validate(); len(errs) != 0 {
+	w := tv.walker()
+	defer w.finished()
+	if errs := w.validate(); len(errs) != 0 {
 		return errs
 	}
 	return nil
@@ -77,6 +80,7 @@ func (tv TypedValue) Validate() error {
 func (tv TypedValue) ToFieldSet() (*fieldpath.Set, error) {
 	s := fieldpath.NewSet()
 	w := tv.walker()
+	defer w.finished()
 	w.leafFieldCallback = func(p fieldpath.Path) { s.Insert(p) }
 	w.nodeFieldCallback = func(p fieldpath.Path) { s.Insert(p) }
 	if errs := w.validate(); len(errs) != 0 {
@@ -203,6 +207,10 @@ func (tv TypedValue) Empty() *TypedValue {
 	return &tv
 }
 
+var mwPool = sync.Pool{
+	New: func() interface{} { return &mergingWalker{} },
+}
+
 func merge(lhs, rhs *TypedValue, rule, postRule mergeRule) (*TypedValue, error) {
 	if lhs.schema != rhs.schema {
 		return nil, errorFormatter{}.
@@ -213,14 +221,27 @@ func merge(lhs, rhs *TypedValue, rule, postRule mergeRule) (*TypedValue, error)
 			errorf("expected objects of the same type, but got %v and %v", lhs.typeRef, rhs.typeRef)
 	}
 
-	mw := mergingWalker{
-		lhs:          &lhs.value,
-		rhs:          &rhs.value,
-		schema:       lhs.schema,
-		typeRef:      lhs.typeRef,
-		rule:         rule,
-		postItemHook: postRule,
-	}
+	mw := mwPool.Get().(*mergingWalker)
+	defer func() {
+		mw.lhs = nil
+		mw.rhs = nil
+		mw.schema = nil
+		mw.typeRef = schema.TypeRef{}
+		mw.rule = nil
+		mw.postItemHook = nil
+		mw.out = nil
+		mw.inLeaf = false
+
+		mwPool.Put(mw)
+	}()
+
+	mw.lhs = &lhs.value
+	mw.rhs = &rhs.value
+	mw.schema = lhs.schema
+	mw.typeRef = lhs.typeRef
+	mw.rule = rule
+	mw.postItemHook = postRule
+
 	errs := mw.merge()
 	if len(errs) > 0 {
 		return nil, errs
diff --git a/typed/validate.go b/typed/validate.go
index 8d7de3f5..0a763247 100644
--- a/typed/validate.go
+++ b/typed/validate.go
@@ -17,17 +17,33 @@ limitations under the License.
 package typed
 
 import (
+	"sync"
+
 	"sigs.k8s.io/structured-merge-diff/fieldpath"
 	"sigs.k8s.io/structured-merge-diff/schema"
 	"sigs.k8s.io/structured-merge-diff/value"
 )
 
+var vPool = sync.Pool{
+	New: func() interface{} { return &validatingObjectWalker{} },
+}
+
 func (tv TypedValue) walker() *validatingObjectWalker {
-	return &validatingObjectWalker{
-		value:   tv.value,
-		schema:  tv.schema,
-		typeRef: tv.typeRef,
-	}
+	v := vPool.Get().(*validatingObjectWalker)
+	v.value = tv.value
+	v.schema = tv.schema
+	v.typeRef = tv.typeRef
+	return v
+}
+
+func (v *validatingObjectWalker) finished() {
+	v.value = value.Value{}
+	v.schema = nil
+	v.typeRef = schema.TypeRef{}
+	v.leafFieldCallback = nil
+	v.nodeFieldCallback = nil
+	v.inLeaf = false
+	vPool.Put(v)
 }
 
 type validatingObjectWalker struct {