Mod 3.2 Operating Systems

• Bounded-Buffer Problem

• Readers and Writers Problem

• Dining-Philosophers Problem

What are the classical problems of Synchronization

Bounded-Buffer Problem

• n buffers, each can hold one item

• Semaphore mutex initialized to the value 1

• Semaphore full initialized to the value 0

• Semaphore empty initialized to the value n

Readers

In Readers-Writers Problem they are the ones who only read the data set; they do not perform any updates

Writers

In Readers-Writers Problem they are the ones who can both read and write

Readers-Writers Problem

• Problem – allow multiple readers to read at the same time

  • Only one single writer can access the shared data at the same time

“First reader-writer”

A situation where a writer process never writes.

• Once a writer is ready to write, no “newly arrived reader” is allowed to read.

Starvation

Both the First reader-writer and Second reader-writer may result in

Readers-Writers Problem

Dining-Philosophers Problem

• N philosophers’ sit at a round table with a bowl of rice in the middle.

• They spend their lives alternating thinking and eating. 

• They do not interact with their neighbors. 

• Occasionally try to pick up 2 chopsticks (one at a time) to eat from bowl

  • Need both to eat, then release both when done

Kernel Synchronization - Windows uses _____ protect access to global resources on uniprocessor systems

spinlocks

Kernel Synchronization - Windows uses _____ on multiprocessor systems

dispatcher objects

Kernel Synchronization - Windows provides user land which may act mutexes, semaphores, events, and timers

Linux Synchronization

On single-CPU system, spinlocks replaced by enabling and disabling kernel preemption

True

True or False

• Linux provides:

  • Semaphores

  • Atomic integers

  • Spinlocks

  • Reader-writer versions of both

POSIX Synchronization

Widely used on UNIX, Linux, and macOS

True

True or False:

• POSIX API provides

  • mutex locks

  • semaphores

  • condition variable

True

True or False:

• Java provides rich set of synchronization features:

  • Java monitors

  • Reentrant locks

  • Semaphores

  • Condition variables

Single lock

Every Java object has associated with it a?

Synchronized

If a method is declared as ___ a calling thread must own the lock for the object.

True

True or False

• If the lock is owned by another thread, the calling thread must wait for the lock until it is released.

Functional programming languages

offer a different paradigm than procedural languages in that they do not maintain state.

Variables

treated as immutable and cannot change state once they have been assigned a value.