Minor enhancement to Win32 locking semantics.

FossilOrigin-Name: ed66ffce57de556e495241cb78af57411691c883e4e512df31904432119c1d10

manifest

@@ -1,5 +1,5 @@
-C Change\san\sunreachable\stestcase()\sinto\san\sassert()
-D 2019-12-18T21:22:40.803
+C Minor\senhancement\sto\sWin32\slocking\ssemantics.
+D 2019-12-19T00:59:01.007
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -512,7 +512,7 @@ F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
 F src/os_unix.c 3e0e519f27683083a465e948e056759a8340728c222b5c394a135e0c57c220bc
-F src/os_win.c 035a813cbd17f355bdcad7ab894af214a9c13a1db8aeac902365350b98cd45a7
+F src/os_win.c 7736ab8e0c222ffaf40d2b9bdb9912e6a0652bf70d1fe52fa22197d3f695e1ca
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 30f20d2263d3717f41a0d9a40f7a3d0f48ce1cfab461b875c6187ead9d6ad1c7
 F src/pager.h 217921e81eb5fe455caa5cda96061959706bcdd29ddb57166198645ef7822ac3
@@ -1852,7 +1852,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 862974312edf00e9d1068115d1a39b7235b7db68b6d86b81d38a12f025a4748e
-R 32a38e4aaf6284494d646d127a601f97
-U drh
-Z f00e4fb5b7f3ab87734a306c50a18bfb
+P 062e00c4d7e30155299339eaefe6cbe01953894baebf0af6d7ab3295b7436eb7
+R 94923d75a62f5e52043a6e48dd8ca11d
+T *branch * win32LockFlags
+T *sym-win32LockFlags *
+T -sym-trunk *
+U mistachkin
+Z e0212d36b82e790dfc5d0112102bec96

manifest.uuid

@@ -1 +1 @@
-062e00c4d7e30155299339eaefe6cbe01953894baebf0af6d7ab3295b7436eb7
+ed66ffce57de556e495241cb78af57411691c883e4e512df31904432119c1d10

src/os_win.c

@@ -3274,8 +3274,10 @@ static int winLock(sqlite3_file *id, int locktype){
   if( pFile->locktype==NO_LOCK
    || (locktype==EXCLUSIVE_LOCK && pFile->locktype<=RESERVED_LOCK)
   ){
+    DWORD dwFlags = SQLITE_LOCKFILE_FLAGS;
     int cnt = 3;
-    while( cnt-->0 && (res = winLockFile(&pFile->h, SQLITE_LOCKFILE_FLAGS,
+    if( osIsNT() && locktype!=EXCLUSIVE_LOCK ) dwFlags=SQLITE_LOCKFILEEX_FLAGS;
+    while( cnt-->0 && (res = winLockFile(&pFile->h, dwFlags,
                                          PENDING_BYTE, 0, 1, 0))==0 ){
       /* Try 3 times to get the pending lock.  This is needed to work
       ** around problems caused by indexing and/or anti-virus software on