Change the mutex interface to be pluggable. This is an incremental checkin, there are still changes to come. (CVS 5227)

FossilOrigin-Name: 597283637bcdc2398bf249b2bbc6ded47ad2de22

6 files changed, 259 insertions, 99 deletions

diff --git a/src/mem2.c b/src/mem2.c
index 311f02dbd..4f97ba2ce 100644
--- a/src/mem2.c
+++ b/src/mem2.c
@@ -19,7 +19,7 @@
 ** This file contains implementations of the low-level memory allocation
 ** routines specified in the sqlite3_mem_methods object.
 **
-** $Id: mem2.c,v 1.30 2008/06/17 15:12:01 drh Exp $
+** $Id: mem2.c,v 1.31 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
@@ -321,7 +321,7 @@ void sqlite3MemSetDefault(void){
 
 /*
 ** Set the number of backtrace levels kept for each allocation.
-** A value of zero turns of backtracing.  The number is always rounded
+** A value of zero turns off backtracing.  The number is always rounded
 ** up to a multiple of 2.
 */
 void sqlite3MemdebugBacktrace(int depth){
diff --git a/src/mutex.c b/src/mutex.c
index 23c0422f6..3eded653b 100644
--- a/src/mutex.c
+++ b/src/mutex.c
@@ -19,10 +19,115 @@
 ** implementation is suitable for testing.
 ** debugging purposes
 **
-** $Id: mutex.c,v 1.20 2008/06/15 02:51:48 drh Exp $
+** $Id: mutex.c,v 1.21 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
+#ifndef SQLITE_MUTEX_NOOP
+/*
+** Initialize the mutex system.
+*/
+int sqlite3_mutex_init(void){ 
+  int rc;
+  if( !sqlite3Config.mutex.xMutexAlloc ){
+    sqlite3_mutex_methods *p = sqlite3DefaultMutex();
+    sqlite3_mutex *pMaster;
+
+    rc = p->xMutexInit();
+    if( rc==SQLITE_OK ){
+      pMaster = p->xMutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
+      p->xMutexEnter(pMaster);
+      assert( sqlite3Config.mutex.xMutexAlloc==0 
+           || sqlite3Config.mutex.xMutexAlloc==p->xMutexAlloc
+      );
+      if( !sqlite3Config.mutex.xMutexAlloc ){
+        sqlite3Config.mutex = *p;
+      }
+      p->xMutexLeave(pMaster);
+    }
+
+  }else{
+    rc = sqlite3Config.mutex.xMutexInit();
+  }
+
+  return rc;
+}
+
+/*
+** Shutdown the mutex system. This call frees resources allocated by
+** sqlite3_mutex_init().
+*/
+int sqlite3_mutex_end(void){
+  int rc = SQLITE_OK;
+  rc = sqlite3Config.mutex.xMutexEnd();
+  return rc;
+}
+
+/*
+** Retrieve a pointer to a static mutex or allocate a new dynamic one.
+*/
+sqlite3_mutex *sqlite3_mutex_alloc(int id){
+  return sqlite3Config.mutex.xMutexAlloc(id);
+}
+
+/*
+** Free a dynamic mutex.
+*/
+void sqlite3_mutex_free(sqlite3_mutex *p){
+  if( p ){
+    sqlite3Config.mutex.xMutexFree(p);
+  }
+}
+
+/*
+** Obtain the mutex p. If some other thread already has the mutex, block
+** until it can be obtained.
+*/
+void sqlite3_mutex_enter(sqlite3_mutex *p){
+  if( p ){
+    sqlite3Config.mutex.xMutexEnter(p);
+  }
+}
+
+/*
+** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
+** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
+*/
+int sqlite3_mutex_try(sqlite3_mutex *p){
+  int rc = SQLITE_OK;
+  if( p ){
+    return sqlite3Config.mutex.xMutexTry(p);
+  }
+  return rc;
+}
+
+/*
+** The sqlite3_mutex_leave() routine exits a mutex that was previously
+** entered by the same thread.  The behavior is undefined if the mutex 
+** is not currently entered. If a NULL pointer is passed as an argument
+** this function is a no-op.
+*/
+void sqlite3_mutex_leave(sqlite3_mutex *p){
+  if( p ){
+    sqlite3Config.mutex.xMutexLeave(p);
+  }
+}
+
+#ifndef NDEBUG
+/*
+** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
+** intended for use inside assert() statements.
+*/
+int sqlite3_mutex_held(sqlite3_mutex *p){
+  return p==0 || sqlite3Config.mutex.xMutexHeld(p);
+}
+int sqlite3_mutex_notheld(sqlite3_mutex *p){
+  return p==0 || sqlite3Config.mutex.xMutexNotheld(p);
+}
+#endif
+
+#endif
+
 #ifdef SQLITE_MUTEX_NOOP_DEBUG
 /*
 ** In this implementation, mutexes do not provide any mutual exclusion.
@@ -39,17 +144,28 @@ struct sqlite3_mutex {
 };
 
 /*
+** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
+** intended for use inside assert() statements.
+*/
+static int noopMutexHeld(sqlite3_mutex *p){
+  return p==0 || p->cnt>0;
+}
+static int noopMutexNotheld(sqlite3_mutex *p){
+  return p==0 || p->cnt==0;
+}
+
+/*
 ** Initialize and deinitialize the mutex subsystem.
 */
-int sqlite3_mutex_init(void){ return SQLITE_OK; }
-int sqlite3_mutex_end(void){ return SQLITE_OK; }
+static int noopMutexInit(void){ return SQLITE_OK; }
+static int noopMutexEnd(void){ return SQLITE_OK; }
 
 /*
 ** The sqlite3_mutex_alloc() routine allocates a new
 ** mutex and returns a pointer to it.  If it returns NULL
 ** that means that a mutex could not be allocated. 
 */
-sqlite3_mutex *sqlite3_mutex_alloc(int id){
+static sqlite3_mutex *noopMutexAlloc(int id){
   static sqlite3_mutex aStatic[6];
   sqlite3_mutex *pNew = 0;
   switch( id ){
@@ -76,8 +192,7 @@ sqlite3_mutex *sqlite3_mutex_alloc(int id){
 /*
 ** This routine deallocates a previously allocated mutex.
 */
-void sqlite3_mutex_free(sqlite3_mutex *p){
-  if( p==0 ) return;
+static void noopMutexFree(sqlite3_mutex *p){
   assert( p->cnt==0 );
   assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
   sqlite3_free(p);
@@ -94,17 +209,13 @@ void sqlite3_mutex_free(sqlite3_mutex *p){
 ** can enter.  If the same thread tries to enter any other kind of mutex
 ** more than once, the behavior is undefined.
 */
-void sqlite3_mutex_enter(sqlite3_mutex *p){
-  if( p ){
-    assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
-    p->cnt++;
-  }
+static void noopMutexEnter(sqlite3_mutex *p){
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || noopMutexNotheld(p) );
+  p->cnt++;
 }
-int sqlite3_mutex_try(sqlite3_mutex *p){
-  if( p ){
-    assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
-    p->cnt++;
-  }
+static int noopMutexTry(sqlite3_mutex *p){
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || noopMutexNotheld(p) );
+  p->cnt++;
   return SQLITE_OK;
 }
 
@@ -114,22 +225,26 @@ int sqlite3_mutex_try(sqlite3_mutex *p){
 ** is undefined if the mutex is not currently entered or
 ** is not currently allocated.  SQLite will never do either.
 */
-void sqlite3_mutex_leave(sqlite3_mutex *p){
-  if( p ){
-    assert( sqlite3_mutex_held(p) );
-    p->cnt--;
-    assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
-  }
+static void noopMutexLeave(sqlite3_mutex *p){
+  assert( sqlite3_mutex_held(p) );
+  p->cnt--;
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
 }
 
-/*
-** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
-** intended for use inside assert() statements.
-*/
-int sqlite3_mutex_held(sqlite3_mutex *p){
-  return p==0 || p->cnt>0;
-}
-int sqlite3_mutex_notheld(sqlite3_mutex *p){
-  return p==0 || p->cnt==0;
+sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+  static sqlite3_mutex_methods sMutex = {
+    noopMutexInit,
+    noopMutexAlloc,
+    noopMutexFree,
+    noopMutexEnter,
+    noopMutexTry,
+    noopMutexLeave,
+    noopMutexEnd,
+
+    noopMutexHeld,
+    noopMutexNotheld
+  };
+
+  return &sMutex;
 }
 #endif /* SQLITE_MUTEX_NOOP_DEBUG */
diff --git a/src/mutex_unix.c b/src/mutex_unix.c
index 4639a8427..2ec52a1a9 100644
--- a/src/mutex_unix.c
+++ b/src/mutex_unix.c
@@ -11,7 +11,7 @@
 *************************************************************************
 ** This file contains the C functions that implement mutexes for pthreads
 **
-** $Id: mutex_unix.c,v 1.8 2008/06/13 18:24:27 drh Exp $
+** $Id: mutex_unix.c,v 1.9 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
@@ -46,10 +46,35 @@ struct sqlite3_mutex {
 #endif
 
 /*
+** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
+** intended for use only inside assert() statements.  On some platforms,
+** there might be race conditions that can cause these routines to
+** deliver incorrect results.  In particular, if pthread_equal() is
+** not an atomic operation, then these routines might delivery
+** incorrect results.  On most platforms, pthread_equal() is a 
+** comparison of two integers and is therefore atomic.  But we are
+** told that HPUX is not such a platform.  If so, then these routines
+** will not always work correctly on HPUX.
+**
+** On those platforms where pthread_equal() is not atomic, SQLite
+** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
+** make sure no assert() statements are evaluated and hence these
+** routines are never called.
+*/
+#ifndef NDEBUG
+static int pthreadMutexHeld(sqlite3_mutex *p){
+  return (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
+}
+static int pthreadMutexNotheld(sqlite3_mutex *p){
+  return p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
+}
+#endif
+
+/*
 ** Initialize and deinitialize the mutex subsystem.
 */
-int sqlite3_mutex_init(void){ return SQLITE_OK; }
-int sqlite3_mutex_end(void){ return SQLITE_OK; }
+static int pthreadMutexInit(void){ return SQLITE_OK; }
+static int pthreadMutexEnd(void){ return SQLITE_OK; }
 
 /*
 ** The sqlite3_mutex_alloc() routine allocates a new
@@ -92,7 +117,7 @@ int sqlite3_mutex_end(void){ return SQLITE_OK; }
 ** mutex types, the same mutex is returned on every call that has
 ** the same type number.
 */
-sqlite3_mutex *sqlite3_mutex_alloc(int iType){
+static sqlite3_mutex *pthreadMutexAlloc(int iType){
   static sqlite3_mutex staticMutexes[] = {
     SQLITE3_MUTEX_INITIALIZER,
     SQLITE3_MUTEX_INITIALIZER,
@@ -147,13 +172,11 @@ sqlite3_mutex *sqlite3_mutex_alloc(int iType){
 ** allocated mutex.  SQLite is careful to deallocate every
 ** mutex that it allocates.
 */
-void sqlite3_mutex_free(sqlite3_mutex *p){
-  if( p ){
-    assert( p->nRef==0 );
-    assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
-    pthread_mutex_destroy(&p->mutex);
-    sqlite3_free(p);
-  }
+static void pthreadMutexFree(sqlite3_mutex *p){
+  assert( p->nRef==0 );
+  assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
+  pthread_mutex_destroy(&p->mutex);
+  sqlite3_free(p);
 }
 
 /*
@@ -167,9 +190,8 @@ void sqlite3_mutex_free(sqlite3_mutex *p){
 ** can enter.  If the same thread tries to enter any other kind of mutex
 ** more than once, the behavior is undefined.
 */
-void sqlite3_mutex_enter(sqlite3_mutex *p){
-  if( p==0 ) return;
-  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
+static void pthreadMutexEnter(sqlite3_mutex *p){
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );
 
 #ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
   /* If recursive mutexes are not available, then we have to grow
@@ -207,10 +229,9 @@ void sqlite3_mutex_enter(sqlite3_mutex *p){
   }
 #endif
 }
-int sqlite3_mutex_try(sqlite3_mutex *p){
+static int pthreadMutexTry(sqlite3_mutex *p){
   int rc;
-  if( p==0 ) return SQLITE_OK;
-  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );
 
 #ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
   /* If recursive mutexes are not available, then we have to grow
@@ -263,8 +284,7 @@ int sqlite3_mutex_try(sqlite3_mutex *p){
 ** is undefined if the mutex is not currently entered or
 ** is not currently allocated.  SQLite will never do either.
 */
-void sqlite3_mutex_leave(sqlite3_mutex *p){
-  if( p==0 ) return;
+static void pthreadMutexLeave(sqlite3_mutex *p){
   assert( sqlite3_mutex_held(p) );
   p->nRef--;
   assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
@@ -284,28 +304,21 @@ void sqlite3_mutex_leave(sqlite3_mutex *p){
 #endif
 }
 
-/*
-** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
-** intended for use only inside assert() statements.  On some platforms,
-** there might be race conditions that can cause these routines to
-** deliver incorrect results.  In particular, if pthread_equal() is
-** not an atomic operation, then these routines might delivery
-** incorrect results.  On most platforms, pthread_equal() is a 
-** comparison of two integers and is therefore atomic.  But we are
-** told that HPUX is not such a platform.  If so, then these routines
-** will not always work correctly on HPUX.
-**
-** On those platforms where pthread_equal() is not atomic, SQLite
-** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
-** make sure no assert() statements are evaluated and hence these
-** routines are never called.
-*/
-#ifndef NDEBUG
-int sqlite3_mutex_held(sqlite3_mutex *p){
-  return p==0 || (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
-}
-int sqlite3_mutex_notheld(sqlite3_mutex *p){
-  return p==0 || p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
+sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+  static sqlite3_mutex_methods sMutex = {
+    pthreadMutexInit,
+    pthreadMutexAlloc,
+    pthreadMutexFree,
+    pthreadMutexEnter,
+    pthreadMutexTry,
+    pthreadMutexLeave,
+    pthreadMutexEnd,
+
+    pthreadMutexHeld,
+    pthreadMutexNotheld
+  };
+
+  return &sMutex;
 }
-#endif
+
 #endif /* SQLITE_MUTEX_PTHREAD */
diff --git a/src/mutex_w32.c b/src/mutex_w32.c
index fcb468aec..fa3f86a08 100644
--- a/src/mutex_w32.c
+++ b/src/mutex_w32.c
@@ -11,7 +11,7 @@
 *************************************************************************
 ** This file contains the C functions that implement mutexes for win32
 **
-** $Id: mutex_w32.c,v 1.7 2008/06/13 18:24:27 drh Exp $
+** $Id: mutex_w32.c,v 1.8 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
@@ -57,12 +57,23 @@ struct sqlite3_mutex {
   }
 #endif /* OS_WINCE */
 
+/*
+** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
+** intended for use only inside assert() statements.
+*/
+static int winMutexHeld(sqlite3_mutex *p){
+  return p->nRef!=0 && p->owner==GetCurrentThreadId();
+}
+static int winMutexNotheld(sqlite3_mutex *p){
+  return p->nRef==0 || p->owner!=GetCurrentThreadId();
+}
+
 
 /*
 ** Initialize and deinitialize the mutex subsystem.
 */
-int sqlite3_mutex_init(void){ return SQLITE_OK; }
-int sqlite3_mutex_end(void){ return SQLITE_OK; }
+static int winMutexInit(void){ return SQLITE_OK; }
+static int winMutexEnd(void){ return SQLITE_OK; }
 
 /*
 ** The sqlite3_mutex_alloc() routine allocates a new
@@ -103,7 +114,7 @@ int sqlite3_mutex_end(void){ return SQLITE_OK; }
 ** mutex types, the same mutex is returned on every call that has
 ** the same type number.
 */
-sqlite3_mutex *sqlite3_mutex_alloc(int iType){
+static sqlite3_mutex *winMutexAlloc(int iType){
   sqlite3_mutex *p;
 
   switch( iType ){
@@ -147,7 +158,7 @@ sqlite3_mutex *sqlite3_mutex_alloc(int iType){
 ** allocated mutex.  SQLite is careful to deallocate every
 ** mutex that it allocates.
 */
-void sqlite3_mutex_free(sqlite3_mutex *p){
+static void winMutexFree(sqlite3_mutex *p){
   assert( p );
   assert( p->nRef==0 );
   assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
@@ -166,17 +177,15 @@ void sqlite3_mutex_free(sqlite3_mutex *p){
 ** can enter.  If the same thread tries to enter any other kind of mutex
 ** more than once, the behavior is undefined.
 */
-void sqlite3_mutex_enter(sqlite3_mutex *p){
-  if( p==0 ) return;
-  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
+static void winMutexEnter(sqlite3_mutex *p){
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
   EnterCriticalSection(&p->mutex);
   p->owner = GetCurrentThreadId(); 
   p->nRef++;
 }
-int sqlite3_mutex_try(sqlite3_mutex *p){
+static int winMutexTry(sqlite3_mutex *p){
   int rc = SQLITE_BUSY;
-  if( p==0 ) return SQLITE_OK;
-  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
+  assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
   /*
   ** The sqlite3_mutex_try() routine is very rarely used, and when it
   ** is used it is merely an optimization.  So it is OK for it to always
@@ -204,8 +213,7 @@ int sqlite3_mutex_try(sqlite3_mutex *p){
 ** is undefined if the mutex is not currently entered or
 ** is not currently allocated.  SQLite will never do either.
 */
-void sqlite3_mutex_leave(sqlite3_mutex *p){
-  if( p==0 ) return;
+static void winMutexLeave(sqlite3_mutex *p){
   assert( p->nRef>0 );
   assert( p->owner==GetCurrentThreadId() );
   p->nRef--;
@@ -213,14 +221,21 @@ void sqlite3_mutex_leave(sqlite3_mutex *p){
   LeaveCriticalSection(&p->mutex);
 }
 
-/*
-** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
-** intended for use only inside assert() statements.
-*/
-int sqlite3_mutex_held(sqlite3_mutex *p){
-  return p==0 || (p->nRef!=0 && p->owner==GetCurrentThreadId());
-}
-int sqlite3_mutex_notheld(sqlite3_mutex *p){
-  return p==0 || p->nRef==0 || p->owner!=GetCurrentThreadId();
+sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+  static sqlite3_mutex_methods sMutex = {
+    winMutexInit,
+    winMutexAlloc,
+    winMutexFree,
+    winMutexEnter,
+    winMutexTry,
+    winMutexLeave,
+    winMutexEnd,
+
+    winMutexHeld,
+    winMutexNotheld
+  };
+
+  return &sMutex;
 }
 #endif /* SQLITE_MUTEX_W32 */
+
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 52e7f5537..592b1e174 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -30,7 +30,7 @@
 ** the version number) and changes its name to "sqlite3.h" as
 ** part of the build process.
 **
-** @(#) $Id: sqlite.h.in,v 1.329 2008/06/17 15:12:01 drh Exp $
+** @(#) $Id: sqlite.h.in,v 1.330 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #ifndef _SQLITE3_H_
 #define _SQLITE3_H_
@@ -5784,6 +5784,20 @@ int sqlite3_mutex_try(sqlite3_mutex*);
 void sqlite3_mutex_leave(sqlite3_mutex*);
 int sqlite3_mutex_end(void);
 
+typedef struct sqlite3_mutex_methods sqlite3_mutex_methods;
+struct sqlite3_mutex_methods {
+  int (*xMutexInit)(void);
+  sqlite3_mutex *(*xMutexAlloc)(int);
+  void (*xMutexFree)(sqlite3_mutex *);
+  void (*xMutexEnter)(sqlite3_mutex *);
+  int (*xMutexTry)(sqlite3_mutex *);
+  void (*xMutexLeave)(sqlite3_mutex *);
+  int (*xMutexEnd)(void);
+  int (*xMutexHeld)(sqlite3_mutex *);
+  int (*xMutexNotheld)(sqlite3_mutex *);
+};
+
+
 /*
 ** CAPI3REF: Mutex Verifcation Routines {F17080}
 **
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index e0b9c4c05..8513074ba 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -11,7 +11,7 @@
 *************************************************************************
 ** Internal interface definitions for SQLite.
 **
-** @(#) $Id: sqliteInt.h,v 1.711 2008/06/17 15:12:01 drh Exp $
+** @(#) $Id: sqliteInt.h,v 1.712 2008/06/17 17:21:18 danielk1977 Exp $
 */
 #ifndef _SQLITEINT_H_
 #define _SQLITEINT_H_
@@ -1739,6 +1739,7 @@ struct Sqlite3Config {
   int bCoreMutex;                   /* True to enable core mutexing */
   int bFullMutex;                   /* True to enable full mutexing */
   sqlite3_mem_methods m;            /* Low-level memory allocation interface */
+  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
   void *pHeap;                      /* Heap storage space */
   sqlite3_int64 nHeap;              /* Size of pHeap[] */
   int mnReq, mxReq;                 /* Min and max memory request sizes */
@@ -1797,6 +1798,8 @@ void *sqlite3PageMalloc(int);
 void sqlite3PageFree(void*);
 void sqlite3MemSetDefault(void);
 
+sqlite3_mutex_methods *sqlite3DefaultMutex(void);
+
 int sqlite3IsNaN(double);
 
 char *sqlite3MPrintf(sqlite3*,const char*, ...);