Final Review David Ferry, Chris Gill CSE 522S - Advanced Operating Systems Washington University in St. Louis St. Louis, MO 63130

CSE 522S – Advanced Operating Systems Exam Scope Questions derived from slides Split between comprehension and analysis Studios useful for analysis & concepts 8 questions 80 minutes 10 minutes per question Does not cover “details” slides (i.e. device drivers) CSE 522S – Advanced Operating Systems

Major Concepts Pre-Midterm Kernel execution: Scheduling: System calls CFS Scheduler Interrupt handlers Real-Time Scheduler Kernel threads Kernel modules Processes: Process creation Process address space CSE 522S – Advanced Operating Systems

CSE 522S – Advanced Operating Systems Exam Concepts Signals: Sockets: Generation & delivery Communication endpoint abstraction Similarity to interrupt Bind, listen, accept Pipes/FIFOs: Shared memory: Anonymous & named Does not use kernel Atomicity Same physical memory Capacity How to impose order? CSE 522S – Advanced Operating Systems

CSE 522S – Advanced Operating Systems Example Question #1 Imagine you are writing two programs that communicate small quantities of data: If neither process is a direct descendent of each other, is the pipe() system call or the mkfifo() system call more appropriate? Why? (4 points) Give one advantage and one disadvantage of using a shared memory region. (4 points) Suppose you initially write your programs with FIFOs, but then want to switch to sockets. What aspect of these interfaces minimizes the amount of re-writing you need to do? (2 points) CSE 522S – Advanced Operating Systems

CSE 522S – Advanced Operating Systems Example Question #2 Recall that some functions are unsafe to be used inside a signal handler. Explain why the function below is unsafe to be used in a main program as well as a signal handler: (2 pts) int temp; void swap( int *a, int *b){ temp = &a; &a = &b; &b = temp; } Suppose you really need to call the above function as a result of a signal and cannot modify it. Give two approaches for doing so. (8 pts) CSE 522S – Advanced Operating Systems

CSE 522S – Advanced Operating Systems Example Question #3 Suppose you have one producer process passing work to multiple consumer processes through a single FIFO. The consumers try to read the FIFO continuously. What is the maximum size of each unit of work, in bytes, on a typical system? Why? (4 pts) Give an example of what might go wrong if the unit of work exceeds your limit given above. (2 pts) Propose a FIFO-based communications scheme for a single-producer, multiple-consumers scenario that supports individual units of work that is greater than this limit. (6 pts) CSE 522S – Advanced Operating Systems