From: Sven Anderson <sven@anderson.de>
Date: Thu, 18 May 2023 19:45:28 +0000 (+0200)
Subject: runtime: let Pinner preallocate a reusable ref array
X-Git-Tag: go1.21rc1~356
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=4bb38fe458cab82711b9a3c96c57a9ea106b044a;p=gostls13.git

runtime: let Pinner preallocate a reusable ref array

With this change a Pinner preallocates an array of 5 pointers for
references to pinned objects. This reduces allocations when a pinner
is reused with up to 5 pinned objects.

This is a follow-up to CL 367296.

Signed-off-by: Sven Anderson <sven@anderson.de>
Change-Id: Ibea0b9ee4d7e39b0341a1da9d8276a4283e4956d
Reviewed-on: https://go-review.googlesource.com/c/go/+/496275
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
---

diff --git a/src/runtime/pinner.go b/src/runtime/pinner.go
index a507a5a3cc..94c9e92432 100644
--- a/src/runtime/pinner.go
+++ b/src/runtime/pinner.go
@@ -28,8 +28,9 @@ type Pinner struct {
 func (p *Pinner) Pin(pointer any) {
 	if p.pinner == nil {
 		p.pinner = new(pinner)
+		p.refs = p.refStore[:0]
 		SetFinalizer(p.pinner, func(i *pinner) {
-			if i.refs != nil {
+			if len(i.refs) != 0 {
 				i.unpin() // only required to make the test idempotent
 				pinnerLeakPanic()
 			}
@@ -46,8 +47,14 @@ func (p *Pinner) Unpin() {
 	p.pinner.unpin()
 }
 
+const (
+	pinnerSize         = 64
+	pinnerRefStoreSize = (pinnerSize - unsafe.Sizeof([]unsafe.Pointer{})) / unsafe.Sizeof(unsafe.Pointer(nil))
+)
+
 type pinner struct {
-	refs []unsafe.Pointer
+	refs     []unsafe.Pointer
+	refStore [pinnerRefStoreSize]unsafe.Pointer
 }
 
 func (p *pinner) unpin() {
@@ -58,7 +65,8 @@ func (p *pinner) unpin() {
 		setPinned(p.refs[i], false)
 		p.refs[i] = nil
 	}
-	p.refs = nil
+	p.refStore = [pinnerRefStoreSize]unsafe.Pointer{}
+	p.refs = p.refStore[:0]
 }
 
 func pinnerGetPtr(i *any) unsafe.Pointer {