When the in single-threaded mode, the sqlite3_mutex_alloc() interface

still returns a non-NULL value.  The mutex doesn't do anything, but it
tests non-NULL.  This way, extensions (or VFSes) that use sqlite3_mutex_alloc()
can tell the difference between an OOM error and mutexes being disabled.

FossilOrigin-Name: 451fd175758983c335aab449fdc4cb838156c4cb

manifest

@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C When\ssqlite3PagerPagecount()\sis\scalled\swithout\sany\slocks,\salways\sreturn\nthe\sphysical\sfile\ssize,\snot\sthe\slogical\sfile\ssize.
-D 2010-05-04T18:50:40
+C When\sthe\sin\ssingle-threaded\smode,\sthe\ssqlite3_mutex_alloc()\sinterface\nstill\sreturns\sa\snon-NULL\svalue.\s\sThe\smutex\sdoesn't\sdo\sanything,\sbut\sit\ntests\snon-NULL.\s\sThis\sway,\sextensions\s(or\sVFSes)\sthat\suse\ssqlite3_mutex_alloc()\ncan\stell\sthe\sdifference\sbetween\san\sOOM\serror\sand\smutexes\sbeing\sdisabled.
+D 2010-05-05T00:05:24
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in d83a0ffef3dcbfb08b410a6c6dd6c009ec9167fb
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -142,9 +142,9 @@ F src/mem2.c 2ee7bdacda8299b5a91cff9f7ee3e46573195c38
 F src/mem3.c 9b237d911ba9904142a804be727cc6664873f8a3
 F src/mem5.c eb7a5cb98915dd7a086fa415ce3a5a0f20d0acff
 F src/memjournal.c f3be374af30588de297dcf678925b2a4758e4135
-F src/mutex.c c04412513619b3a763f3484bb412336fa3a3fbd9
+F src/mutex.c e2358d8f9a9021ab0bba4d511bb701e471e6e5f6
 F src/mutex.h 6fde601e55fa6c3fae768783c439797ab84c87c6
-F src/mutex_noop.c 5f58eaa31f2d742cb8957a747f7887ae98f16053
+F src/mutex_noop.c 7dcd084c1ecb6258b7da824fa0feb7d9ebd537d5
 F src/mutex_os2.c 20477db50cf3817c2f1cd3eb61e5c177e50231db
 F src/mutex_unix.c 04a25238abce7e3d06b358dcf706e26624270809
 F src/mutex_w32.c 4cc201c1bfd11d1562810554ff5500e735559d7e
@@ -171,7 +171,7 @@ F src/select.c c03d8a0565febcde8c6a12c5d77d065fddae889b
 F src/shell.c c40427c7245535a04a9cb4a417b6cc05c022e6a4
 F src/sqlite.h.in 7afbe9fb794092cb38bd3cfab72c39560ce0def5
 F src/sqlite3ext.h 69dfb8116af51b84a029cddb3b35062354270c89
-F src/sqliteInt.h e7f1368eb56d8a410e510bcffb9ca5795060c58c
+F src/sqliteInt.h 9819b45610abeca390176243a9a31758c1f0ac7a
 F src/sqliteLimit.h 196e2f83c3b444c4548fc1874f52f84fdbda40f3
 F src/status.c 4df6fe7dce2d256130b905847c6c60055882bdbe
 F src/table.c 2cd62736f845d82200acfa1287e33feb3c15d62e
@@ -812,14 +812,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P b15b67fa14ff77963f470678ff6188c63be8e079
-R 90a516a40aed68998882df9ec8564c82
+P 4016b422286587beda7323052d27821adb1fed73
+R 87640419095dfdb05fcc49f65da51e46
 U drh
-Z a30cf60f66607a4454bb94232875c47b
+Z 50e1e779e0d4bec5a929210a4c6c0526
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-=5Otc
+iD8DBQFL4LZKoxKgR168RlERAvf5AJ4yZOjWI5iQUOpLK97VFh220LzPgwCdHHWu
+b+V9an+7FFUytUxF3xEa9/c=
+=qvND
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manifest.uuid

@@ -1 +1 @@
-4016b422286587beda7323052d27821adb1fed73
+451fd175758983c335aab449fdc4cb838156c4cb

src/mutex.c

@@ -31,23 +31,26 @@ static SQLITE_WSD int mutexIsInit = 0;
 */
 int sqlite3MutexInit(void){ 
   int rc = SQLITE_OK;
-  if( sqlite3GlobalConfig.bCoreMutex ){
-    if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
-      /* 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
-      ** the default implementation into the sqlite3GlobalConfig structure.
-      */
-      sqlite3_mutex_methods *pFrom = sqlite3DefaultMutex();
-      sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
+  if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
+    /* 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
+    ** the default implementation into the sqlite3GlobalConfig structure.
+    */
+    sqlite3_mutex_methods *pFrom;
+    sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
 
-      memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc));
-      memcpy(&pTo->xMutexFree, &pFrom->xMutexFree,
-             sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree));
-      pTo->xMutexAlloc = pFrom->xMutexAlloc;
+    if( sqlite3GlobalConfig.bCoreMutex ){
+      pFrom = sqlite3DefaultMutex();
+    }else{
+      pFrom = sqlite3NoopMutex();
     }
-    rc = sqlite3GlobalConfig.mutex.xMutexInit();
+    memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc));
+    memcpy(&pTo->xMutexFree, &pFrom->xMutexFree,
+           sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree));
+    pTo->xMutexAlloc = pFrom->xMutexAlloc;
   }
+  rc = sqlite3GlobalConfig.mutex.xMutexInit();
 
 #ifdef SQLITE_DEBUG
   GLOBAL(int, mutexIsInit) = 1;
@@ -77,7 +80,6 @@ int sqlite3MutexEnd(void){
 ** Retrieve a pointer to a static mutex or allocate a new dynamic one.
 */
 sqlite3_mutex *sqlite3_mutex_alloc(int id){
-  if( !sqlite3GlobalConfig.bCoreMutex ) return 0;
 #ifndef SQLITE_OMIT_AUTOINIT
   if( sqlite3_initialize() ) return 0;
 #endif

src/mutex_noop.c

@@ -28,7 +28,7 @@
 #include "sqliteInt.h"
 
 
-#if defined(SQLITE_MUTEX_NOOP) && !defined(SQLITE_DEBUG)
+#ifndef SQLITE_DEBUG
 /*
 ** Stub routines for all mutex methods.
 **
@@ -44,7 +44,7 @@ static void noopMutexEnter(sqlite3_mutex *p){ return; }
 static int noopMutexTry(sqlite3_mutex *p){ return SQLITE_OK; }
 static void noopMutexLeave(sqlite3_mutex *p){ return; }
 
-sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+sqlite3_mutex_methods *sqlite3NoopMutex(void){
   static sqlite3_mutex_methods sMutex = {
     noopMutexInit,
     noopMutexEnd,
@@ -60,9 +60,9 @@ sqlite3_mutex_methods *sqlite3DefaultMutex(void){
 
   return &sMutex;
 }
-#endif /* defined(SQLITE_MUTEX_NOOP) && !defined(SQLITE_DEBUG) */
+#endif /* !SQLITE_DEBUG */
 
-#if defined(SQLITE_MUTEX_NOOP) && defined(SQLITE_DEBUG)
+#ifdef SQLITE_DEBUG
 /*
 ** In this implementation, error checking is provided for testing
 ** and debugging purposes.  The mutexes still do not provide any
@@ -165,7 +165,7 @@ static void debugMutexLeave(sqlite3_mutex *p){
   assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(p) );
 }
 
-sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+sqlite3_mutex_methods *sqlite3NoopMutex(void){
   static sqlite3_mutex_methods sMutex = {
     debugMutexInit,
     debugMutexEnd,
@@ -181,4 +181,14 @@ sqlite3_mutex_methods *sqlite3DefaultMutex(void){
 
   return &sMutex;
 }
-#endif /* defined(SQLITE_MUTEX_NOOP) && defined(SQLITE_DEBUG) */
+#endif /* SQLITE_DEBUG */
+
+/*
+** If compiled with SQLITE_MUTEX_NOOP, then the no-op mutex implementation
+** is used regardless of the run-time threadsafety setting.
+*/
+#ifdef SQLITE_MUTEX_NOOP
+sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+  return sqliteNoopMutex();
+}
+#endif /* SQLITE_MUTEX_NOOP */

src/sqliteInt.h

@@ -2537,6 +2537,7 @@ const sqlite3_mem_methods *sqlite3MemGetMemsys5(void);
 
 #ifndef SQLITE_MUTEX_OMIT
   sqlite3_mutex_methods *sqlite3DefaultMutex(void);
+  sqlite3_mutex_methods *sqlite3NoopMutex(void);
   sqlite3_mutex *sqlite3MutexAlloc(int);
   int sqlite3MutexInit(void);
   int sqlite3MutexEnd(void);