From ed0284a08d9960b681653961d327aaf1b631978a Mon Sep 17 00:00:00 2001
From: Joe Mistachkin <sqlite@mistachkin.com>
Date: Thu, 9 Nov 2017 23:24:29 +0000
Subject: [PATCH] Avoid superfluous SHM unlock call in the Win32 VFS.

---
 src/os_win.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/os_win.c b/src/os_win.c
index 2ee4ad1acf..086bbf90aa 100644
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -3834,6 +3834,7 @@ static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
 */
 static int winLockSharedMemory(winShmNode *pShmNode){
   int rc = winShmSystemLock(pShmNode, WINSHM_WRLCK, WIN_SHM_DMS, 1);
+
   if( rc==SQLITE_OK ){
     if( pShmNode->isReadonly ){
       pShmNode->isUnlocked = 1;
@@ -3846,7 +3847,10 @@ static int winLockSharedMemory(winShmNode *pShmNode){
     }
   }
 
-  winShmSystemLock(pShmNode, WINSHM_UNLCK, WIN_SHM_DMS, 1);
+  if( rc==SQLITE_OK ){
+    winShmSystemLock(pShmNode, WINSHM_UNLCK, WIN_SHM_DMS, 1);
+  }
+
   return winShmSystemLock(pShmNode, WINSHM_RDLCK, WIN_SHM_DMS, 1);
 }
 
-- 
2.11.4.GIT