Add the SQLITE_CONFIG_MUTEX symbol for use with sqlite3_config(). (CVS 5228)

FossilOrigin-Name: af1835bb5f5e3fb78d782c7c287e20db169e883f

3 files changed, 21 insertions, 6 deletions

diff --git a/src/main.c b/src/main.c
index 803c0ec4b..af2576e45 100644
--- a/src/main.c
+++ b/src/main.c
@@ -14,7 +14,7 @@
 ** other files are for internal use by SQLite and should not be
 ** accessed by users of the library.
 **
-** $Id: main.c,v 1.445 2008/06/16 20:51:16 drh Exp $
+** $Id: main.c,v 1.446 2008/06/17 18:57:49 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 #include <ctype.h>
@@ -76,9 +76,7 @@ int sqlite3_initialize(void){
   if( sqlite3IsInit ) return SQLITE_OK;
   rc = sqlite3_mutex_init();
   if( rc==SQLITE_OK ){
-#ifndef SQLITE_MUTEX_NOOP
     sqlite3_mutex *pMutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER);
-#endif
     sqlite3_mutex_enter(pMutex);
     if( sqlite3IsInit==0 ){
       sqlite3IsInit = 1;
@@ -153,6 +151,11 @@ int sqlite3_config(int op, ...){
       sqlite3Config.m = *va_arg(ap, sqlite3_mem_methods*);
       break;
     }
+    case SQLITE_CONFIG_MUTEX: {
+      /* Specify an alternative mutex implementation */
+      sqlite3Config.mutex = *va_arg(ap, sqlite3_mutex_methods*);
+      break;
+    }
     case SQLITE_CONFIG_MEMSTATUS: {
       /* Enable or disable the malloc status collection */
       sqlite3Config.bMemstat = va_arg(ap, int);
diff --git a/src/mutex.c b/src/mutex.c
index 3eded653b..46bb82d71 100644
--- a/src/mutex.c
+++ b/src/mutex.c
@@ -19,7 +19,7 @@
 ** implementation is suitable for testing.
 ** debugging purposes
 **
-** $Id: mutex.c,v 1.21 2008/06/17 17:21:18 danielk1977 Exp $
+** $Id: mutex.c,v 1.22 2008/06/17 18:57:49 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
@@ -30,12 +30,24 @@
 int sqlite3_mutex_init(void){ 
   int rc;
   if( !sqlite3Config.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 sqlite3Config structure.
+    **
+    ** The danger is that although sqlite3_config() is not a threadsafe
+    ** API, sqlite3_initialize() is, and so multiple threads may be
+    ** attempting to run this function simultaneously. To guard write
+    ** access to the sqlite3Config structure, the 'MASTER' static mutex
+    ** is obtained before modifying it.
+    */
     sqlite3_mutex_methods *p = sqlite3DefaultMutex();
     sqlite3_mutex *pMaster;
 
     rc = p->xMutexInit();
     if( rc==SQLITE_OK ){
       pMaster = p->xMutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
+      assert(pMaster);
       p->xMutexEnter(pMaster);
       assert( sqlite3Config.mutex.xMutexAlloc==0 
            || sqlite3Config.mutex.xMutexAlloc==p->xMutexAlloc
@@ -45,7 +57,6 @@ int sqlite3_mutex_init(void){
       }
       p->xMutexLeave(pMaster);
     }
-
   }else{
     rc = sqlite3Config.mutex.xMutexInit();
   }
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 592b1e174..d9b8921aa 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 1.330 2008/06/17 17:21:18 danielk1977 Exp $
+** @(#) $Id: sqlite.h.in,v 1.331 2008/06/17 18:57:49 danielk1977 Exp $
 */
 #ifndef _SQLITE3_H_
 #define _SQLITE3_H_
@@ -1050,6 +1050,7 @@ struct sqlite3_mem_methods {
 #define SQLITE_CONFIG_SERIALIZED    3  /* nil */
 #define SQLITE_CONFIG_MALLOC        4  /* sqlite3_mem_methods* */
 #define SQLITE_CONFIG_MEMSTATUS     5  /* boolean */
+#define SQLITE_CONFIG_MUTEX         6  /* sqlite3_mutex_methods* */
 
 /* These options are to be added later.  Currently unused and undocumented. */
 #define SQLITE_CONFIG_HEAP          6  /* void*, int64, min, max, tmp */