[Discuss-gnuradio] Try to understand the stream in Gnu Radio

[Zhonghua]

Hi all,

After a period of using gnu radio, I have a problem of how to understand 
the stream. I got an information from a literature says: 'From the high 
level point-of-view, infinite streams of data flow through the ports. At 
the C++ level,streams are dealt with in convenient sized pieces, 
represented as contiguous arrays of the underlying type.' In almost each 
signal processing block we can see the definition of 'general_work' has 
this format:
     general_work(int noutput_items,
                     gr_vector_int &ninput_items,
                     gr_vector_const_void_star &input_items,
                     gr_vector_void_star &output_items)
Some literatures say the 'noutput_items' variable represents the items 
number of one piece of the stream.  So the first question is what on 
earth the size of this variable? where dose it be specified? For example 
if A block connects to B block, how can ensure the 'noutput_items' of A 
block equal to the 'ninput_items' (presume B block only has one input 
stream).
In an concrete instance, in gr_squelch_base_cc.cc, we can see the last 
program as:
    if (d_state != ST_MUTED)
       out[j++] = in[i]*gr_complex(d_envelope, 0.0);
    else
       if (!d_gate)
          out[j++] = 0.0;
If we set d_gate as False(Actually in case of high sample rate it has to 
be set as False), when the input power is lower than the threshold(means 
the d_state should be as ST_MUTED), the out[j] shall get nothing. That 
means at this point there is no output data. So how the sequential block 
recognise this point? For instance the sequential block is 
ieee802_15_4_demod, how could it know where is this lost point? If only 
one point lost from the squelch block, is that means the whole piece of 
stream and even the whole package could not be demodulated correctly?
We can set the instance in more precise condition. If there are two 
pieces of stream: stream A and stream B. Assume each noutput_items is 
10, that is to say we have A[0], A[1] ....to A[9] and B[0] to B[9]. If 
A[0] has lost, then the stream entering into the sequential demodulation 
block is A[0](lost),A[1]....A[9]? Or is A[1],A[2]....B[0]?
If A[0] is valid, A[1] has lost, dose that mean the first piece of 
stream would not be demodulated correctly? If one package need both 
these two pieces of stream, dose it mean this package would not be 
demodulated correctly?

Any answer is greatly appreciated.

Sincerely,

Zhonghua