#vulnerable code 
                                void connectIfNeededAndDoOp(GenericCallback<Void> op) {
        boolean doOpNow;

        // common case without lock first
        if (channel != null && state == ConnectionState.CONNECTED) {
            doOpNow = true;
        } else {

            synchronized (this) {
                // check again under lock
                if (channel != null && state == ConnectionState.CONNECTED) {
                    doOpNow = true;
                } else {

                    // if reached here, channel is either null (first connection
                    // attempt),
                    // or the channel is disconnected
                    doOpNow = false;

                    // connection attempt is still in progress, queue up this
                    // op. Op will be executed when connection attempt either
                    // fails
                    // or
                    // succeeds
                    pendingOps.add(op);

                    connect();
                }
            }
        }

        if (doOpNow) {
            op.operationComplete(BKException.Code.OK, null);
        }

    } 
                            #location 5 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                void connectIfNeededAndDoOp(GenericCallback<Void> op) {
        boolean doOpNow;

        synchronized (this) {
            if (channel != null && state == ConnectionState.CONNECTED) {
                doOpNow = true;
            } else {
                // if reached here, channel is either null (first connection
                // attempt),
                // or the channel is disconnected
                doOpNow = false;

                // connection attempt is still in progress, queue up this
                // op. Op will be executed when connection attempt either
                // fails
                // or
                // succeeds
                pendingOps.add(op);

                connect();
            }
        }

        if (doOpNow) {
            op.operationComplete(BKException.Code.OK, null);
        }
    }