How does the OS handle concurrency in multi-core systems?

• Thread Affinity: Binds threads to specific cores.
• Load Balancing: Distributes threads evenly across cores.
• Lock-free Algorithms: Reduce contention on shared resources.
• Cache Coherence Protocols: Ensure consistency of shared data across cores.

What is hardware support for concurrency?

• Test-and-Set Instructions: Atomic operation to test and modify a lock.
• Compare-and-Swap (CAS): Atomic instruction to update a value only if it matches an expected value.
• Memory Barriers: Ensure proper ordering of memory operations in multi-threaded environments.

What are non-blocking synchronization techniques?

• Lock-Free: At least one thread makes progress without being blocked.
• Wait-Free: All threads make progress within a bounded time.
• Obstruction-Free: Progress is guaranteed in the absence of contention.

How do condition variables differ from semaphores?

Feature	Condition Variables	Semaphores
Purpose	Waiting for conditions	Counting or mutual exclusion
State Retention	Do not retain state if no waiters	Retain state (can count signals)
Usage	Used with a lock	Standalone synchronization tool

What is the Peterson’s Algorithm?

Peterson’s algorithm is a classic solution for achieving mutual exclusion in concurrent programming.

• It uses two shared variables: a flag for each process and a turn variable to decide which process enters the critical section.
• It satisfies mutual exclusion, progress, and bounded waiting conditions.

How does the operating system implement context switching in concurrency?

Context switching involves saving the state of a currently running process and restoring the state of another process.

• Steps: Save CPU registers → Save process state → Load new process state → Restore registers.
• The kernel handles this efficiently to maintain concurrency.

What are lock-free and wait-free algorithms?

• Lock-Free Algorithms:
• Ensure that at least one thread makes progress in a finite number of steps.
• Example: Compare-and-Swap (CAS) operations.
• Wait-Free Algorithms:
• Ensure all threads make progress in a bounded number of steps.
• Useful for real-time systems.

What are soft and hard real-time systems in concurrency?

1. Soft Real-Time Systems:
   • Allow occasional deadline misses.
   • Examples: Multimedia streaming.
2. Hard Real-Time Systems:
   • Must meet all deadlines strictly.
   • Examples: Airbag systems in cars.

What is the difference between shared memory and message passing in concurrency?

Aspect	Shared Memory	Message Passing
Communication	Directly through shared space	Exchange messages via the OS
Performance	Faster but requires synchronization	Slower due to message overhead
Complexity	Needs careful synchronization	Easier to implement

What are the differences between condition variables and semaphores?

Aspect	Condition Variables	Semaphores
Purpose	Wait for specific conditions	Counting or mutual exclusion
State Persistence	Do not retain state if no waiters	Retain state (count persists)
Locking	Used with a lock	Standalone synchronization tool

What is the difference between concurrency and parallelism?

Aspect	Concurrency	Parallelism
Definition	Multiple tasks in progress	Tasks running simultaneously
Requirement	Can run on a single core	Requires multiple cores
Focus	Managing access to shared resources	Increasing execution speed

How are deadlocks detected and resolved?

1. Detection:
   • Use a wait-for graph to identify cycles.
   • Use algorithms like the Banker’s algorithm for resource allocation states.
2. Resolution:
   • Terminate one or more processes.
   • Preempt and reallocate resources.