Chapter 6: Process Synchronization

• background: concurrent access to shared data may result in data inconsistency
• consumer-producer problem: counter itself will have synchronization issues
• Race Condition: the outcome depends on which process finished first, which is uncontrollable
• Solution: 1) non-preemptive scheduling: can be used in kernel mode only. 2) critical section
• Critical Section
  • N processes are competing to use shared data
  • each process has a code segment, called critical section (CS), in which the shared data is accessed
  • ensure mutual exclusion: only one process can be in its CS at a time
• Critical Section Requirements
  • Mutual Exclusion: only one process in CS at a time
  • Progress: No deadlock --- It ensures the system doesn't freeze. If the CS is empty, someone must be allowed to enter.
  • Bounded Waiting: No starvation --- It ensures fairness. An individual process cannot be forced to wait forever while others cut in line.
• Entry Section: code to request permission to enter CS
• Exit Section: code to release CS

Software Solutions