OS Chapter 5: Process Synchronization

Process Synchronization

• Process synchronization is necessary to maintain data consistency in concurrent execution environments.

The Critical-Section Problem

• The critical-section problem arises when multiple processes access shared data concurrently, leading to data inconsistency.
• The problem involves designing a protocol to ensure that only one process can execute its critical section at a time.

Solution to Critical-Section Problem

• The solution must satisfy three conditions: • Mutual Exclusion: no two processes can execute their critical sections simultaneously. • Progress: a process waiting to enter its critical section will eventually do so. • Bounded Waiting: a limit exists on the number of times other processes can enter their critical sections before the waiting process enters its critical section.

Critical Section Handling in OS

• Two approaches to critical-section handling exist, depending on whether the kernel is preemptive or non-preemptive.
• Preemptive kernel: allows preemption of a process when running in kernel mode.
• Non-preemptive kernel: runs until it exits kernel mode, blocks, or voluntarily yields CPU.

Synchronization Hardware

• Many systems provide hardware support for implementing critical section code using locks.
• Uniprocessors can disable interrupts to protect critical regions, but this approach is inefficient on multiprocessor systems.

Mutex Locks

• Mutex locks are software tools that solve the critical section problem.
• A mutex lock protects a critical section by requiring a process to acquire the lock before entering the critical section and releasing it afterwards.
• Mutex locks can be implemented using hardware atomic instructions, but they require busy waiting, making them spinlocks.

Semaphore

• Semaphore is a synchronization tool that provides more sophisticated ways to synchronize process activities than mutex locks.