Specifying an invalid mutex implementation (via SQLITE_CONFIG_MUTEX) should cause the default one to be used instead.

FossilOrigin-Name: 1a97bc81ccfc88f2dd527dff16e9e395718675bc

manifest

@@ -1,5 +1,5 @@
-C Clarify\sthe\snew\smutex\simplementation\sreset\slogic\sin\ssqlite3_shutdown().
-D 2015-09-12T03:40:13.463
+C Specifying\san\sinvalid\smutex\simplementation\s(via\sSQLITE_CONFIG_MUTEX)\sshould\scause\sthe\sdefault\sone\sto\sbe\sused\sinstead.
+D 2015-09-12T04:19:51.382
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in f85066ce844a28b671aaeeff320921cd0ce36239
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -314,7 +314,7 @@ F src/mem3.c 61c9d47b792908c532ca3a62b999cf21795c6534
 F src/mem5.c 61eeb90134f9a5be6c2e68d8daae7628b25953fb
 F src/memjournal.c 3eb2c0b51adbd869cb6a44780323f05fa904dc85
 F src/msvc.h d9ba56c6851227ab44b3f228a35f3f5772296495
-F src/mutex.c 58c1a764c37ba3c139cfb9cd8c7449eb7b4d68d9
+F src/mutex.c 87bd895b69359cf01d611fa72849237087151e21
 F src/mutex.h 779d588e3b7756ec3ecf7d78cde1d84aba414f85
 F src/mutex_noop.c f03e26ba8258399da23b51234f6b6a97197c1900
 F src/mutex_unix.c a72043f2560147d8e85fe48a6aef682896deb3a0
@@ -1386,7 +1386,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 7562f1fbede70b19bbbb928e0a534203528b5b65
-R 3ac5767399d8383f18e381780f08b08c
+P f9a034834e6c6e32ac350cf48bec981490e533ad
+R bf73c19c36cb2ae09dd34d5e1c1598fa
 U mistachkin
-Z fd5ef4befe69774364afb3ff74061ec0
+Z 7d9d0679bd87dd4450cebce4f9dd2531

manifest.uuid

@@ -1 +1 @@
-f9a034834e6c6e32ac350cf48bec981490e533ad
+1a97bc81ccfc88f2dd527dff16e9e395718675bc

src/mutex.c

@@ -26,6 +26,32 @@ static SQLITE_WSD int mutexIsInit = 0;
 
 
 #ifndef SQLITE_MUTEX_OMIT
+/*
+** This structure is for use by sqlite3MutexInit() only.  It represents an
+** invalid mutex implementation (i.e. one where all the function pointers
+** are null).
+*/
+static const sqlite3_mutex_methods mutexNullMethods = {
+  0, /* xMutexInit */
+  0, /* xMutexEnd */
+  0, /* xMutexAlloc */
+  0, /* xMutexFree */
+  0, /* xMutexEnter */
+  0, /* xMutexTry */
+  0, /* xMutexLeave */
+  0, /* xMutexHeld */
+  0  /* xMutexNotheld */
+};
+
+/*
+** Returns non-zero if the currently configured mutex implemention is
+** invalid (i.e. all of its function pointers are null).
+*/
+static int mutexIsInvalid(void){
+  return memcmp(&sqlite3GlobalConfig.mutex, &mutexNullMethods,
+                sizeof(sqlite3_mutex_methods))==0;
+}
+
 /*
 ** Copies a mutex implementation.  Both arguments must point to valid
 ** memory.
@@ -51,7 +77,7 @@ static void mutexCopy(
 int sqlite3MutexInit(void){ 
   int rc;
   if( sqlite3CompareAndSwap((void * volatile *)&sqlite3GlobalConfig.pMutex,
-                            0, &sqlite3GlobalConfig.mutex)==0 ){
+                   0, &sqlite3GlobalConfig.mutex)==0 || mutexIsInvalid() ){
     /* If the xMutexAlloc method has not been set, then the user did not
     ** install a mutex implementation via sqlite3_config() prior to 
     ** sqlite3_initialize() being called. This block copies pointers to