Restore the sqlite3_mutex_try() optimization on winNT systems. (CVS 4402)

FossilOrigin-Name: 3aace2fa91e96038f7a32366828ac7520470fa67

manifest

@@ -1,5 +1,5 @@
-C Remove\sthe\sunixFile.isOpen\svariable\s(no\slonger\sin\suse).\s(CVS\s4401)
+C Restore\sthe\ssqlite3_mutex_try()\soptimization\son\swinNT\ssystems.\s(CVS\s4402)
-D 2007-09-05T13:56:32
+D 2007-09-05T14:30:42
 F Makefile.in cbfb898945536a8f9ea8b897e1586dd1fdbcc5db
 F Makefile.linux-gcc 65241babba6faf1152bf86574477baab19190499
 F README 9c4e2d6706bdcc3efdd773ce752a8cdab4f90028
@@ -108,7 +108,7 @@ F src/mutex.c 40e5ba09d56863895882a0204d93832e9960ea78
 F src/mutex.h 079fa6fe9da18ceb89e79012c010594c6672addb
 F src/mutex_os2.c d47e9bd495583dd31263d8fe55160a31eb600a3c
 F src/mutex_unix.c ff77650261a245035b79c5c8a174f4e05d3cae8a
-F src/mutex_w32.c 2812771e75148c58a62ca05bbeb9a8dd6ec46307
+F src/mutex_w32.c d2c56fb81aca10af1577bdae2a4083eb2505f8ee
 F src/os.c 198c6c55cbdbe5b9c3105070c88fcc077d1b2447
 F src/os.h 53e65427899ed5697d79749d646e6a297b70171a
 F src/os_common.h 98862f120ca6bf7a48ce8b16f158b77d00bc9d2f
@@ -569,7 +569,7 @@ F www/tclsqlite.tcl 8be95ee6dba05eabcd27a9d91331c803f2ce2130
 F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
 F www/version3.tcl 890248cf7b70e60c383b0e84d77d5132b3ead42b
 F www/whentouse.tcl fc46eae081251c3c181bd79c5faef8195d7991a5
-P 630fc71f3df5ab6129ddff9d8184893ecc6cf3c5
+P 1786e9c881a67fbf8bd014d643590534c8c601dc
-R 9a78b375d5424edc5f5d67c6a4158c36
+R 13dbaebf3174563b1064b0b1bbb0d310
-U danielk1977
+U drh
-Z 26fe5592b03efb24fd754f70db25a373
+Z 14476c6d97c0081a9542a49eeb3e06d4

manifest.uuid

@@ -1 +1 @@
-1786e9c881a67fbf8bd014d643590534c8c601dc
+3aace2fa91e96038f7a32366828ac7520470fa67

src/mutex_w32.c

@@ -11,7 +11,7 @@
 *************************************************************************
 ** This file contains the C functions that implement mutexes for win32
 **
-** $Id: mutex_w32.c,v 1.3 2007/09/04 22:31:37 drh Exp $
+** $Id: mutex_w32.c,v 1.4 2007/09/05 14:30:42 drh Exp $
 */
 #include "sqliteInt.h"
 
@@ -31,6 +31,33 @@ struct sqlite3_mutex {
   DWORD owner;               /* Thread holding this mutex */
 };
 
+/*
+** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
+** or WinCE.  Return false (zero) for Win95, Win98, or WinME.
+**
+** Here is an interesting observation:  Win95, Win98, and WinME lack
+** the LockFileEx() API.  But we can still statically link against that
+** API as long as we don't call it win running Win95/98/ME.  A call to
+** this routine is used to determine if the host is Win95/98/ME or
+** WinNT/2K/XP so that we will know whether or not we can safely call
+** the LockFileEx() API.
+*/
+#if OS_WINCE
+# define mutexIsNT()  (1)
+#else
+  static int mutexIsNT(void){
+    static int osType = 0;
+    if( osType==0 ){
+      OSVERSIONINFO sInfo;
+      sInfo.dwOSVersionInfoSize = sizeof(sInfo);
+      GetVersionEx(&sInfo);
+      osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
+    }
+    return osType==2;
+  }
+#endif /* OS_WINCE */
+
+
 /*
 ** The sqlite3_mutex_alloc() routine allocates a new
 ** mutex and returns a pointer to it.  If it returns NULL
@@ -141,16 +168,10 @@ void sqlite3_mutex_enter(sqlite3_mutex *p){
   p->nRef++;
 }
 int sqlite3_mutex_try(sqlite3_mutex *p){
-  /* The TryEnterCriticalSection() interface is not available on all
-  ** windows systems.  Since sqlite3_mutex_try() is only used as an
-  ** optimization, we can skip it on windows. */
-  return SQLITE_BUSY;
-
-#if 0  /* Not Available */
   int rc;
   assert( p );
   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
-  if( TryEnterCriticalSection(&p->mutex) ){
+  if( mutexIsNT() && TryEnterCriticalSection(&p->mutex) ){
     p->owner = GetCurrentThreadId();
     p->nRef++;
     rc = SQLITE_OK;
@@ -158,7 +179,6 @@ int sqlite3_mutex_try(sqlite3_mutex *p){
     rc = SQLITE_BUSY;
   }
   return rc;
-#endif
 }
 
 /*