Fix an obscure race condition that can occur when multiple threads, shared cache and DDL statements are combined. Enhance notify2.test to test this scenario. (CVS 6373)

FossilOrigin-Name: 92ec5975123284aff3a69ee16c397d9e2a844c0b

src/prepare.c

@@ -13,7 +13,7 @@
 ** interface, and routines that contribute to loading the database schema
 ** from disk.
 **
-** $Id: prepare.c,v 1.111 2009/03/19 18:51:07 danielk1977 Exp $
+** $Id: prepare.c,v 1.112 2009/03/23 17:11:27 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
@@ -91,7 +91,7 @@ int sqlite3InitCallback(void *pInit, int argc, char **argv, char **NotUsed){
       pData->rc = rc;
       if( rc==SQLITE_NOMEM ){
         db->mallocFailed = 1;
-      }else if( rc!=SQLITE_INTERRUPT ){
+      }else if( rc!=SQLITE_INTERRUPT && (rc&0xff)!=SQLITE_LOCKED ){
         corruptSchema(pData, argv[0], zErr);
       }
       sqlite3DbFree(db, zErr);

src/test_thread.c

@@ -14,7 +14,7 @@
 ** test that sqlite3 database handles may be concurrently accessed by 
 ** multiple threads. Right now this only works on unix.
 **
-** $Id: test_thread.c,v 1.12 2009/03/19 07:58:31 danielk1977 Exp $
+** $Id: test_thread.c,v 1.13 2009/03/23 17:11:27 danielk1977 Exp $
 */
 
 #include "sqliteInt.h"
@@ -117,8 +117,10 @@ static Tcl_ThreadCreateType tclScriptThread(ClientData pSqlThread){
   Tcl_CreateObjCommand(interp, "sqlthread", sqlthread_proc, pSqlThread, 0);
 #if defined(OS_UNIX) && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
   Tcl_CreateObjCommand(interp, "sqlite3_blocking_step", blocking_step_proc,0,0);
-  Tcl_CreateObjCommand(
-      interp, "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc,0,0);
+  Tcl_CreateObjCommand(interp, 
+      "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc, (void *)1, 0);
+  Tcl_CreateObjCommand(interp, 
+      "sqlite3_nonblocking_prepare_v2", blocking_prepare_v2_proc, 0, 0);
 #endif
   Sqlitetest1_Init(interp);
   Sqlitetest_mutex_Init(interp);
@@ -544,6 +546,7 @@ static int blocking_step_proc(
 
 /*
 ** Usage: sqlite3_blocking_prepare_v2 DB sql bytes ?tailvar?
+** Usage: sqlite3_nonblocking_prepare_v2 DB sql bytes ?tailvar?
 */
 static int blocking_prepare_v2_proc(
   void * clientData,
@@ -558,6 +561,7 @@ static int blocking_prepare_v2_proc(
   sqlite3_stmt *pStmt = 0;
   char zBuf[50];
   int rc;
+  int isBlocking = !(clientData==0);
 
   if( objc!=5 && objc!=4 ){
     Tcl_AppendResult(interp, "wrong # args: should be \"", 
@@ -568,7 +572,12 @@ static int blocking_prepare_v2_proc(
   zSql = Tcl_GetString(objv[2]);
   if( Tcl_GetIntFromObj(interp, objv[3], &bytes) ) return TCL_ERROR;
 
-  rc = sqlite3_blocking_prepare_v2(db, zSql, bytes, &pStmt, objc>=5?&zTail : 0);
+  if( isBlocking ){
+    rc = sqlite3_blocking_prepare_v2(db, zSql, bytes, &pStmt, &zTail);
+  }else{
+    rc = sqlite3_prepare_v2(db, zSql, bytes, &pStmt, &zTail);
+  }
+
   assert(rc==SQLITE_OK || pStmt==0);
   if( zTail && objc>=5 ){
     if( bytes>=0 ){
@@ -603,8 +612,10 @@ int SqlitetestThread_Init(Tcl_Interp *interp){
   Tcl_CreateObjCommand(interp, "clock_seconds", clock_seconds_proc, 0, 0);
 #if defined(OS_UNIX) && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
   Tcl_CreateObjCommand(interp, "sqlite3_blocking_step", blocking_step_proc,0,0);
-  Tcl_CreateObjCommand(
-      interp, "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc,0,0);
+  Tcl_CreateObjCommand(interp, 
+      "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc, (void *)1, 0);
+  Tcl_CreateObjCommand(interp, 
+      "sqlite3_nonblocking_prepare_v2", blocking_prepare_v2_proc, 0, 0);
 #endif
   return TCL_OK;
 }

src/vdbe.c

@@ -43,7 +43,7 @@
 ** in this file for details.  If in doubt, do not deviate from existing
 ** commenting and indentation practices when changing or adding code.
 **
-** $Id: vdbe.c,v 1.827 2009/03/18 10:33:02 danielk1977 Exp $
+** $Id: vdbe.c,v 1.828 2009/03/23 17:11:27 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 #include "vdbeInt.h"
@@ -4371,33 +4371,58 @@ case OP_CreateTable: {          /* out2-prerelease */
 ** then runs the new virtual machine.  It is thus a re-entrant opcode.
 */
 case OP_ParseSchema: {
-  char *zSql;
   int iDb = pOp->p1;
-  const char *zMaster;
-  InitData initData;
-
   assert( iDb>=0 && iDb<db->nDb );
-  if( !pOp->p2 && !DbHasProperty(db, iDb, DB_SchemaLoaded) ){
-    break;
+
+  /* If pOp->p2 is 0, then this opcode is being executed to read a
+  ** single row, for example the row corresponding to a new index
+  ** created by this VDBE, from the sqlite_master table. It only
+  ** does this if the corresponding in-memory schema is currently
+  ** loaded. Otherwise, the new index definition can be loaded along
+  ** with the rest of the schema when it is required.
+  **
+  ** Although the mutex on the BtShared object that corresponds to
+  ** database iDb (the database containing the sqlite_master table
+  ** read by this instruction) is currently held, it is necessary to
+  ** obtain the mutexes on all attached databases before checking if
+  ** the schema of iDb is loaded. This is because, at the start of
+  ** the sqlite3_exec() call below, SQLite will invoke 
+  ** sqlite3BtreeEnterAll(). If all mutexes are not already held, the
+  ** iDb mutex may be temporarily released to avoid deadlock. If 
+  ** this happens, then some other thread may delete the in-memory 
+  ** schema of database iDb before the SQL statement runs. The schema
+  ** will not be reloaded becuase the db->init.busy flag is set. This
+  ** can result in a "no such table: sqlite_master" or "malformed
+  ** database schema" error being returned to the user.
+  */
+  assert( sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
+  sqlite3BtreeEnterAll(db);
+  if( pOp->p2 || DbHasProperty(db, iDb, DB_SchemaLoaded) ){
+    const char *zMaster = SCHEMA_TABLE(iDb);
+    char *zSql;
+    InitData initData;
+    initData.db = db;
+    initData.iDb = pOp->p1;
+    initData.pzErrMsg = &p->zErrMsg;
+    zSql = sqlite3MPrintf(db,
+       "SELECT name, rootpage, sql FROM '%q'.%s WHERE %s",
+       db->aDb[iDb].zName, zMaster, pOp->p4.z);
+    if( zSql==0 ){
+      rc = SQLITE_NOMEM;
+    }else{
+      (void)sqlite3SafetyOff(db);
+      assert( db->init.busy==0 );
+      db->init.busy = 1;
+      initData.rc = SQLITE_OK;
+      assert( !db->mallocFailed );
+      rc = sqlite3_exec(db, zSql, sqlite3InitCallback, &initData, 0);
+      if( rc==SQLITE_OK ) rc = initData.rc;
+      sqlite3DbFree(db, zSql);
+      db->init.busy = 0;
+      (void)sqlite3SafetyOn(db);
+    }
   }
-  zMaster = SCHEMA_TABLE(iDb);
-  initData.db = db;
-  initData.iDb = pOp->p1;
-  initData.pzErrMsg = &p->zErrMsg;
-  zSql = sqlite3MPrintf(db,
-     "SELECT name, rootpage, sql FROM '%q'.%s WHERE %s",
-     db->aDb[iDb].zName, zMaster, pOp->p4.z);
-  if( zSql==0 ) goto no_mem;
-  (void)sqlite3SafetyOff(db);
-  assert( db->init.busy==0 );
-  db->init.busy = 1;
-  initData.rc = SQLITE_OK;
-  assert( !db->mallocFailed );
-  rc = sqlite3_exec(db, zSql, sqlite3InitCallback, &initData, 0);
-  if( rc==SQLITE_OK ) rc = initData.rc;
-  sqlite3DbFree(db, zSql);
-  db->init.busy = 0;
-  (void)sqlite3SafetyOn(db);
+  sqlite3BtreeLeaveAll(db);
   if( rc==SQLITE_NOMEM ){
     goto no_mem;
   }