From 14237397985b709a8d207e676db5a5fc9a05d989 Mon Sep 17 00:00:00 2001
From: Nuno Cruces <ncruces@users.noreply.github.com>
Date: Sat, 2 Nov 2024 11:02:38 +0000
Subject: [PATCH] Refactor, speed.

---
 vfs/const.go    |  5 +++++
 vfs/shm_bsd.go  |  4 +---
 vfs/shm_copy.go | 21 ++++++++++++---------
 vfs/shm_ofd.go  |  6 ------
 4 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/vfs/const.go b/vfs/const.go
index e80437be..a47aa807 100644
--- a/vfs/const.go
+++ b/vfs/const.go
@@ -234,4 +234,9 @@ const (
 	_SHM_LOCK      _ShmFlag = 2
 	_SHM_SHARED    _ShmFlag = 4
 	_SHM_EXCLUSIVE _ShmFlag = 8
+
+	_SHM_NLOCK = 8
+	_SHM_BASE  = 120
+	_SHM_DMS   = _SHM_BASE + _SHM_NLOCK
+	_SHM_CLOSE = _SHM_UNLOCK | _SHM_SHARED | _SHM_EXCLUSIVE
 )
diff --git a/vfs/shm_bsd.go b/vfs/shm_bsd.go
index 079c8f42..4d2984eb 100644
--- a/vfs/shm_bsd.go
+++ b/vfs/shm_bsd.go
@@ -14,8 +14,6 @@ import (
 	"github.com/ncruces/go-sqlite3/internal/util"
 )
 
-const _SHM_NLOCK = 8
-
 type vfsShmFile struct {
 	*os.File
 	info os.FileInfo
@@ -51,7 +49,7 @@ func (s *vfsShm) Close() error {
 	defer vfsShmFilesMtx.Unlock()
 
 	// Unlock everything.
-	s.shmLock(0, _SHM_NLOCK, _SHM_UNLOCK)
+	s.shmLock(0, _SHM_NLOCK, _SHM_CLOSE)
 
 	// Decrease reference count.
 	if s.vfsShmFile.refs > 0 {
diff --git a/vfs/shm_copy.go b/vfs/shm_copy.go
index 9f7f5860..a4132d0f 100644
--- a/vfs/shm_copy.go
+++ b/vfs/shm_copy.go
@@ -11,10 +11,7 @@ import (
 	"github.com/tetratelabs/wazero/api"
 )
 
-const (
-	_SHM_NLOCK     = 8
-	_WALINDEX_PGSZ = 32768
-)
+const _WALINDEX_PGSZ = 32768
 
 type vfsShmBuffer struct {
 	shared []byte // +checklocks:Mutex
@@ -52,7 +49,7 @@ func (s *vfsShm) Close() error {
 	defer vfsShmBuffersMtx.Unlock()
 
 	// Unlock everything.
-	s.shmLock(0, _SHM_NLOCK, _SHM_UNLOCK)
+	s.shmLock(0, _SHM_NLOCK, _SHM_CLOSE)
 
 	// Decrease reference count.
 	if s.vfsShmBuffer.refs > 0 {
@@ -132,9 +129,10 @@ func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	s.Lock()
 	defer s.Unlock()
 
-	if flags&_SHM_UNLOCK == 0 {
+	switch {
+	case flags&_SHM_LOCK != 0:
 		s.shmAcquire()
-	} else {
+	case flags&_SHM_EXCLUSIVE != 0:
 		s.shmRelease()
 	}
 
@@ -222,6 +220,7 @@ func (s *vfsShm) shmBarrier() {
 //
 // Finally, we have the WAL-index hash tables,
 // which are only modified holding the exclusive WAL_WRITE_LOCK.
+// Also, aHash isn't modified unless aPgno changes.
 //
 // Since all the data is either redundant+checksummed,
 // 4 byte aligned, or modified under an exclusive lock,
@@ -238,7 +237,7 @@ func (s *vfsShm) shmAcquire() {
 		shared := shmPage(s.shared[i0:i1])
 		shadow := shmPage(s.shadow[i0:i1])
 		privat := shmPage(util.View(s.mod, p, _WALINDEX_PGSZ))
-		if *shadow == *shared {
+		if shmPageEq(shadow, shared) {
 			continue
 		}
 		for i, shared := range shared {
@@ -259,7 +258,7 @@ func (s *vfsShm) shmRelease() {
 		shared := shmPage(s.shared[i0:i1])
 		shadow := shmPage(s.shadow[i0:i1])
 		privat := shmPage(util.View(s.mod, p, _WALINDEX_PGSZ))
-		if *shadow == *privat {
+		if shmPageEq(shadow, privat) {
 			continue
 		}
 		for i, privat := range privat {
@@ -275,3 +274,7 @@ func shmPage(s []byte) *[_WALINDEX_PGSZ / 4]uint32 {
 	p := (*uint32)(unsafe.Pointer(unsafe.SliceData(s)))
 	return (*[_WALINDEX_PGSZ / 4]uint32)(unsafe.Slice(p, _WALINDEX_PGSZ/4))
 }
+
+func shmPageEq(p1, p2 *[_WALINDEX_PGSZ / 4]uint32) bool {
+	return *(*[_WALINDEX_PGSZ / 8]uint32)(p1[:]) == *(*[_WALINDEX_PGSZ / 8]uint32)(p2[:])
+}
diff --git a/vfs/shm_ofd.go b/vfs/shm_ofd.go
index bf047550..019fc7ab 100644
--- a/vfs/shm_ofd.go
+++ b/vfs/shm_ofd.go
@@ -15,12 +15,6 @@ import (
 	"github.com/ncruces/go-sqlite3/internal/util"
 )
 
-const (
-	_SHM_NLOCK = 8
-	_SHM_BASE  = 120
-	_SHM_DMS   = _SHM_BASE + _SHM_NLOCK
-)
-
 type vfsShm struct {
 	*os.File
 	path     string