SQLite

/*
** Global linked list of SchemaPool objects. Read and write access must
** be protected by the SQLITE_MUTEX_STATIC_MASTER mutex.
*/
static SchemaPool *SQLITE_WSD schemaPoolList = 0;

#ifdef SQLITE_TEST
/*
** Return a pointer to the head of the linked list of SchemaPool objects.
** This is used by the virtual table in file test_schemapool.c.
*/
SchemaPool *sqlite3SchemaPoolList(void){ return schemaPoolList; }
#endif

/*
** Check that the schema of db iDb is writable (either because it is the 
** temp db schema or because the db handle was opened without
** SQLITE_OPEN_REUSE_SCHEMA). If so, do nothing. Otherwise, leave an 
** error in the Parse object.
*/
void sqlite3SchemaWritable(Parse *pParse, int iDb){
  if( iDb!=1 && (pParse->db->openFlags & SQLITE_OPEN_REUSE_SCHEMA) 
   && IN_DECLARE_VTAB==0
  ){
    sqlite3ErrorMsg(pParse, "attempt to modify read-only schema");
  }
}

/*
** The schema object passed as the only argument was allocated using
** sqlite3_malloc() and then populated using the usual mechanism. This
** function frees both the Schema object and its contents.
*/
static void schemaDelete(Schema *pSchema){
  sqlite3SchemaClear((void*)pSchema);
  sqlite3_free(pSchema);
}

/*
** When this function is called, the database connection Db must be
** using a schema-pool (Db.pSPool!=0) and must currently have Db.pSchema
** set to point to a populated schema object checked out from the 
** schema-pool. It is also assumed that the STATIC_MASTER mutex is held.
** This function returns the Schema object to the schema-pool and sets
** Db.pSchema to point to the schema-pool's static, empty, Schema object.
*/
static void schemaRelease(Db *pDb){
  assert( pDb->pSPool && pDb->pSchema );
  assert( pDb->pSchema->schemaFlags & DB_SchemaLoaded );
  assert( sqlite3_mutex_held(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER)) );

  pDb->pSchema->pNext = pDb->pSPool->pSchema;
  pDb->pSPool->pSchema = pDb->pSchema;
  pDb->pSchema = &pDb->pSPool->sSchema;

  assert( (pDb->pSchema->schemaFlags & DB_SchemaLoaded)==0 );
}

/*
** The schema for database iDb of database handle db, which was opened
** with SQLITE_OPEN_REUSE_SCHEMA, has just been parsed. This function either
** finds a matching SchemaPool object on the global list (schemaPoolList) or
** else allocates a new one and sets the Db.pSPool variable accordingly.
**
** SQLITE_OK is returned if no error occurs, or an SQLite error code 
** (SQLITE_NOMEM) otherwise.
*/
int sqlite3SchemaConnect(sqlite3 *db, int iDb, u64 cksum){
  Schema *pSchema = db->aDb[iDb].pSchema;
  SchemaPool *p;

  assert( pSchema && iDb!=1 && db->aDb[iDb].pSPool==0 );

  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );

  db->aDb[iDb].pSPool = p;
  return (p ? SQLITE_OK : SQLITE_NOMEM);
}

/*
** If parameter iDb is 1 (the temp db), or if connection handle db was not
** opened with the SQLITE_OPEN_REUSE_SCHEMA flag, this function is a no-op.
** Otherwise, it disconnects from the schema-pool associated with database
** iDb, assuming it is connected.
**
** If parameter bNew is true, then Db.pSchema is set to point to a new, empty,
** Schema object obtained from sqlite3_malloc(). Or, if bNew is false, then
** Db.pSchema is set to NULL before returning.
**
** If the bNew parameter is true, then this function may allocate memory. 
** If the allocation attempt fails, then SQLITE_NOMEM is returned and the
** schema-pool is not disconnected from. Or, if no OOM error occurs, 
** SQLITE_OK is returned.
*/
int sqlite3SchemaDisconnect(sqlite3 *db, int iDb, int bNew){
  int rc = SQLITE_OK;
  if( IsReuseSchema(db) && iDb!=1 ){
    Db *pDb = &db->aDb[iDb];
    SchemaPool *pSPool = pDb->pSPool;
    assert_schema_state_ok(db);
    assert( pDb->pSchema );

      pRet->pNext = 0;
    }
    sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  }
  return pRet;
}

/*
** Return all sharable schemas held by database handle db back to their
** respective schema-pools. Db.pSchema variables are left pointing to
** the static, empty, Schema object owned by each schema-pool.
*/
void sqlite3SchemaReleaseAll(sqlite3 *db){
  int i;
  assert_schema_state_ok(db);
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  for(i=0; i<db->nDb; i++){
    if( i!=1 ){
      Db *pDb = &db->aDb[i];
      if( pDb->pSPool && DbHasProperty(db,i,DB_SchemaLoaded) ){
        schemaRelease(pDb);
      }
    }
  }
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
}

/*
** Release any sharable schema held by connection iDb of database handle
** db. Db.pSchema is left pointing to the static, empty, Schema object
** owned by the schema-pool.
*/
void sqlite3SchemaRelease(sqlite3 *db, int iDb){
  Db *pDb = &db->aDb[iDb];
  assert( iDb!=1 );
  assert_schema_state_ok(db);
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  if( pDb->pSPool && DbHasProperty(db, iDb, DB_SchemaLoaded) ){
    schemaRelease(pDb);
  }
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
}

/*
** In most cases, this function finds and returns the schema associated 
** with BTree handle pBt, creating a new one if necessary. However, if
** the database handle was opened with the SQLITE_OPEN_REUSE_SCHEMA flag
** specified, a new, empty, Schema object in memory obtained by 
** sqlite3_malloc() is always returned.
*/
Schema *sqlite3SchemaGet(sqlite3 *db, Btree *pBt){
  Schema *p;
  if( pBt && (db->openFlags & SQLITE_OPEN_REUSE_SCHEMA)==0 ){
    p = (Schema *)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
  }else{
    p = (Schema *)sqlite3DbMallocZero(0, sizeof(Schema));

  4  { ALTER TABLE t1 RENAME TO t3 }
  5  { ALTER TABLE t1 ADD COLUMN xyz }
  6  { VACUUM }
  7  { DROP INDEX i1 }
  8  { DROP TABLE t1 }
  9  { DROP TRIGGER tr1 }
  10 { ANALYZE }
  11 { ALTER TABLE t1 RENAME z TO zzz }
} {
  do_catchsql_test 1.5.$tn $sql {1 {attempt to modify read-only schema}}
}

#-------------------------------------------------------------------------
#
reset_db