[Discuss-gnuradio] How to check if more input is available on an input stream

[Mir Ali]

Hi, 
I have a simple question. I have a block that has 2 input streams and the inputs are consumed at different rates. For each 1 input consumed on the first input stream N inputs are consumed in the second stream. 

The forecast function and set_multiple call of this block are as shown below,

my_new_block::forecast(int noutput_items,gr_vector_int &ninput_items_required){
    assert(noutput_items % N==0); # the 
    
    
    int items_on_first_input_stream = noutput_items; 
    int items_on_second_input_stream = noutput_items/(8*N);
    ninput_items_required[0]=items_on_first_input_stream;
    ninput_items_required[1]=items_on_data_input_stream;
    }


 { 
           set_output_multiple(8*N); # the output items are a multiple of 8*N.

}
For each (8*N) inputs consumed on second stream 1 input is consumed on first stream.
If the first stream has uninterrupted supply but the second one doesn't then how should I check if input is available on the second stream. Will the input_vector contain NULL values when nothing is in it? If it is true should i just do 

if(second_stream[next_item]==null){
.......
}

Please clarify.

Thanks
Ali