Process Synchronization Lecture Notes

Introduction to Process Synchronization

• Focus on understanding:
  • What is process synchronization?
  • Why do we need it?
  • Its importance in operating systems.

Cooperating Processes

• Definition: A cooperating process can affect or be affected by other processes executing in the system.
• Two ways cooperating processes can share data:
  1. Logical address space: Sharing both code and data.
  2. Files or messages: Sharing data only through these.

Problem with Concurrent Access

• Data Inconsistency: Occurs when multiple processes manipulate shared data concurrently.
• Importance of synchronization to ensure orderly execution of processes sharing a logical address space.

Example: Shared Memory Systems

• Producer-Consumer Problem:
  • Producer: Produces information.
  • Consumer: Consumes information.
  • Example scenarios:
    • Compilers producing assembly code for assemblers.
    • Web servers producing web pages for clients.

Buffer Types

• Bounded Buffer: Has a fixed size.
  • Producer waits if the buffer is full.
  • Consumer waits if the buffer is empty.
• Unbounded Buffer: No practical size limit.

Implementation of a Bounded Buffer

• Use a variable (e.g., counter) to track items in the buffer:
  • Incremented by the producer when an item is added.
  • Decremented by the consumer when an item is consumed.

Race Conditions

• Example scenario with counter variable:
  • Initial value: 5.
  • Concurrent execution of counter++ (producer) and counter-- (consumer).
• Possible outcomes after concurrent execution:
  • Can result in counter values: 4, 5, or 6.
  • Correct outcome should be 5.
• Race Condition: Occurs when the outcome of execution depends on the order of access.

Machine-Level Operations

• Understanding how counter++ and counter-- work at the machine level:
  • Counter++:
    1. Load counter value into a register.
    2. Increment register.
    3. Store register value back into counter.
  • Counter--:
    1. Load counter value into another register.
    2. Decrement register.
    3. Store register value back into counter.

Conclusion

• Need for process synchronization to prevent data inconsistency (race conditions).
• Various techniques will be discussed in future chapters to maintain data consistency.
• Core objective: Ensure orderly execution of cooperating processes.