Disallow attaching the same database multiple times to the same db connection

in shared cache mode, since doing so leads to deadlock. (CVS 6578)

FossilOrigin-Name: 715f14f1dcaf604d4794bf3e18e245d4f8c5d5a9

2 files changed, 25 insertions, 4 deletions

diff --git a/src/attach.c b/src/attach.c
index d5495361b..d0f81766b 100644
--- a/src/attach.c
+++ b/src/attach.c
@@ -11,7 +11,7 @@
 *************************************************************************
 ** This file contains code used to implement the ATTACH and DETACH commands.
 **
-** $Id: attach.c,v 1.87 2009/04/30 05:40:34 drh Exp $
+** $Id: attach.c,v 1.88 2009/04/30 13:30:33 drh Exp $
 */
 #include "sqliteInt.h"
 
@@ -119,7 +119,7 @@ static void attachFunc(
     if( aNew==0 ) return;
   }
   db->aDb = aNew;
-  aNew = &db->aDb[db->nDb++];
+  aNew = &db->aDb[db->nDb];
   memset(aNew, 0, sizeof(*aNew));
 
   /* Open the database file. If the btree is successfully opened, use
@@ -129,7 +129,11 @@ static void attachFunc(
   rc = sqlite3BtreeFactory(db, zFile, 0, SQLITE_DEFAULT_CACHE_SIZE,
                            db->openFlags | SQLITE_OPEN_MAIN_DB,
                            &aNew->pBt);
-  if( rc==SQLITE_OK ){
+  db->nDb++;
+  if( rc==SQLITE_CONSTRAINT ){
+    rc = SQLITE_ERROR;
+    zErrDyn = sqlite3MPrintf(db, "database is already attached");
+  }else if( rc==SQLITE_OK ){
     Pager *pPager;
     aNew->pSchema = sqlite3SchemaGet(db, aNew->pBt);
     if( !aNew->pSchema ){
diff --git a/src/btree.c b/src/btree.c
index 315991eb5..acc4aaadd 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btree.c,v 1.601 2009/04/30 09:10:38 danielk1977 Exp $
+** $Id: btree.c,v 1.602 2009/04/30 13:30:33 drh Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** See the header comment on "btreeInt.h" for additional information.
@@ -1401,6 +1401,12 @@ static int btreeInvokeBusyHandler(void *pArg){
 ** database file will be deleted when sqlite3BtreeClose() is called.
 ** If zFilename is ":memory:" then an in-memory database is created
 ** that is automatically destroyed when it is closed.
+**
+** If the database is already opened in the same database connection
+** and we are in shared cache mode, then the open will fail with an
+** SQLITE_CONSTRAINT error.  We cannot allow two or more BtShared
+** objects in the same database connection since doing so will lead
+** to problems with locking.
 */
 int sqlite3BtreeOpen(
   const char *zFilename,  /* Name of the file containing the BTree database */
@@ -1466,6 +1472,17 @@ int sqlite3BtreeOpen(
         assert( pBt->nRef>0 );
         if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager))
                  && sqlite3PagerVfs(pBt->pPager)==pVfs ){
+          int iDb;
+          for(iDb=db->nDb-1; iDb>=0; iDb--){
+            Btree *pExisting = db->aDb[iDb].pBt;
+            if( pExisting && pExisting->pBt==pBt ){
+              sqlite3_mutex_leave(mutexShared);
+              sqlite3_mutex_leave(mutexOpen);
+              sqlite3_free(zFullPathname);
+              sqlite3_free(p);
+              return SQLITE_CONSTRAINT;
+            }
+          }
           p->pBt = pBt;
           pBt->nRef++;
           break;