#vulnerable code 
                                public void shutdown() {
        this.isShutDown = true;

        ConnAdapter conn = managedConn;
        if (conn != null)
            conn.detach();

        synchronized (this) {
            try {
                if (uniquePoolEntry != null) // and connection open?
                    uniquePoolEntry.shutdown();
            } catch (IOException iox) {
                // ignore
                log.debug("Problem while shutting down manager.", iox);
            } finally {
                uniquePoolEntry = null;
                managedConn = null;
            }
        }
    } 
                            #location 4 
                            #vulnerability type UNSAFE_GUARDED_BY_ACCESS
#fixed code
                                public void shutdown() {
        this.isShutDown = true;
        synchronized (this) {
            try {
                if (uniquePoolEntry != null) // and connection open?
                    uniquePoolEntry.shutdown();
            } catch (IOException iox) {
                // ignore
                log.debug("Problem while shutting down manager.", iox);
            } finally {
                uniquePoolEntry = null;
                managedConn = null;
            }
        }
    }