Read-write locks, Operating System

Assignment Help:

Consider a large web-based database. In some sense, Google is sort of like this. There might be many users who want to read from the database, but only a few users who are allowed to write to the database. If we use standard locks to control access to the database, the application will be much slower than it could be with a more clever type of lock.

Suppose we have one object that is shared among several threads. Suppose also that each thread is either a reader or a writer. Readers only read data but never modify it, while writers read and modify data. If we know which threads are reading and which ones are writing, what can we do to increase concurrency?

First, we have to prevent two writers from writing at the same time. In addition, a reader cannot read while a writer is writing. There is no problem, however in allowing lots of readers to read at the same time. Read-write locks achieve this, and can greatly improve performance for this sort of application.

Note that the lock is the same for both readers andwriters (called 'rw' in the slides), but the readers use an rlock() on the lock and writers use a wlock() on the same lock. Writers requesting a wlock() will have to wait until all readers and writers have released the lock. Readers requesting a rlock() can acquire it even if other readers are holding the lock. Readers however will still have to wait until any writer holding the lock releases the lock.


Related Discussions:- Read-write locks

Page-table lookups, How exactly is a page table used to look up an address?...

How exactly is a page table used to look up an address? The CPU has a page table base register (PTBR)which points to the base (entry 0) of the level-0 page table. Each process h

Name two differences between logical and physical addresses, Q. Name two di...

Q. Name two differences between logical and physical addresses? Answer: A logical address doesn't refer to an actual existing address rather it refers to an abstract address in

Plot a function for value of heights, The performance of a file system depe...

The performance of a file system depends upon the cache hit rate (fraction of blocks found in the cache). If it takes 1 msec to satisfy a request from the cache, but 40 msec to sat

Elimination of common sub expression - code optimizatin, Elimination of com...

Elimination of common sub expression during code optimization An optimizing transformation is a rule for rewriting a section of a program to enhance its execution efficiency wi

Define entry section and exit section, Define entry section and exit sectio...

Define entry section and exit section. The critical section problem is to design a protocol that the processes can use to cooperate. Every process must request permission  to e

Prolog application, 1. Problem Domain You will be considering the Wumpus ...

1. Problem Domain You will be considering the Wumpus world introduced in Russell and Norvig (2009) Chapter 7. For this programming assignment you'll use Prolog's ability to do in

Define the sleep (sec) function, Define the Sleep (sec) Function Sleep ...

Define the Sleep (sec) Function Sleep function suspends execution of this process for sec number of seconds. While this function is used in our example for consistency, other f

Explain internal file structure, Internal file structure All disk I/O i...

Internal file structure All disk I/O is performed in units of single block, and all blocks are the similar size. It is unlikely that the physical record size will exactly match

Catalogue the design goals of windows xp, Q. Catalogue the design goals of ...

Q. Catalogue the design goals of Windows XP. Answer: Design goals comprise security and reliability and Windows and POSIX application compatibility with high performance and ex

Explain partitions and mounting, Partitions and mounting A disk can be ...

Partitions and mounting A disk can be sliced into many partitions, or a partition can span multiple disks. Every partition can be either "raw", having no file system, or "cooke

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd