Why noi in block Gnuradio is changed every time........

[sp h]

I developed a block Gnuradio that works with samples block type is sync block. i used a for that i can print samples

             for(int i=0;i<noi;i++)

Why every time noi in gnuradio is changed...i used USRP and UHD source...

but in my custom block noi size is not fixed..how can i fixed it.......

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