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segfault when disconnecting from db with server side prepare

From: "Scot Loach" <sloach(at)sandvine(dot)com>
To: <pgsql-odbc(at)postgresql(dot)org>
Subject: segfault when disconnecting from db with server side prepare
Date: 2004-09-19 14:29:07
Message-ID: A8535F8D62F3644997E91F4F66E341FC1BB2F1@exchange.sandvine.com (view raw or flat)
Thread:
Lists: pgsql-odbc
If I enable server side prepare (UseServerSidePrepare=1 in my DSN) and connect to the database, execute a query, then disconnect, the following code path is taken:
SQL_Disconnect calls PGAPI_Disconnect
PGAPI_Disconnect calls CC_Cleanup
CC_Cleanup iterates through its statements:

/* Free all the stmts on this connection */
for (i = 0; i < self->num_stmts; i++)
{       
        stmt = self->stmts[i];
        if (stmt)
        {
                stmt->hdbc = NULL;      /* prevent any more dbase interactions */
                SC_Destructor(stmt);
                self->stmts[i] = NULL;
        }
}

SC_Destructor calls SC_initialize_stmts(self, TRUE)
SC_Initialize_stmts calls SC_set_prepared(self, FALSE), which dereferences the hdbc pointer, which was set to null in the code block above:

void
SC_set_prepared(StatementClass *stmt, BOOL prepared)
{       
        if (prepared == stmt->prepared)
                return;
        if (!prepared)
        {       
                ConnectionClass *conn = SC_get_conn(stmt);
*** CRASH ***   if (CONN_CONNECTED == conn->status)
                {       
                        QResultClass    *res;
                        char dealloc_stmt[128];
                        
                        sprintf(dealloc_stmt, "DEALLOCATE _PLAN%0x", stmt);
                        res = CC_send_query(conn, dealloc_stmt, NULL, 0);
                        if (res)
                                QR_Destructor(res);
                }
        }
        stmt->prepared = prepared;
}

                
The SC_set_prepared function is trying to deallocate the query plan on the server side - is this necessary if we're shutting down the connection? (anyway, the socket has already been closed before the statements are deallocated.)

I think the proper way to fix this is to simply add a check for a null pointer in the SC_set_prepared function, but I wanted to ask here first since I don't know if this will have any unforseen consequences.


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Next:From: Dave PageDate: 2004-09-20 07:39:10
Subject: Re: segfault when disconnecting from db with server side prepare
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Subject: Re: Access export overflow

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