You have 3 threads running: the main() thread, srd1, and srd2. (There are also other threads running, but you can ignore those for now.) Each of the 3 threads of interest are pretty much off doing their own thing, so I'm not sure what you mean by "control transfer from one block to another." Think of it as 3 tasks, each executing on its own, and see if that helps.
Of course one of the threads has some control over the other two, AND the other two are both doing the same task, but that helps demonstrate how the 3 threads are related while they perform their tasks.
Though your use of deprecated methods simplifies this little demo, don't use suspend() and resume() in a real project.