What happens if you use wait0 in a child that itself does not have any child? Consider a program that opens a file (i.e., with the open) system call and then calls fork0 to create a new process A_ Can both the child and parent write to the file? B If the parent process closes the file (e.g., using fclose0), can the child process still write on the file? How does a timer interrupt useful in the implementation of limited direct execution? What is a multiprogramming OS environment? Consider a program that creates a child process, and then in the child closes standard output (STDOUT_FILENO). What happens if the child calls printf0 to print something after closing the descriptor? Can the parent print something using printf after the child process closes STDOUT FILENO? Describe how arguments of functions are passed between the user-level implementation of a system call and its kernel-level implementation. Ilustrate your answer with code extract from OS/161 What are the main states of a thread/process in OS/161? In OS/161, what happens when a thread terminates? Explain what the functions thread exit0, exorcise0, and thread destroy0 do when threads terminate