Read-write locks, Operating System

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.

Posted Date: 3/12/2013 5:28:34 AM | Location : United States







Related Discussions:- Read-write locks, Assignment Help, Ask Question on Read-write locks, Get Answer, Expert's Help, Read-write locks Discussions

Write discussion on Read-write locks
Your posts are moderated
Related Questions
Briefly discuss on real-time scheduling? It is divided into two types.  Hard real-time systems are needed to complete a critical task within a guaranteed amount of time. T

Q. More than one disk drive is able to be attached to a SCSI bus. Especially a fast wide SCSI-II bus can be connected to at most 15 disk drives. Remember that this bus has a bandw

? FREE ASSOCIATION ASSIGNMENTS of multiprograming

What are the five major activities of an operating system in regard to file management? The creation and deletion of files The creation and deletion of directories The s

Regard as a computer system that runs 5000 jobs per month with no deadlock-prevention or deadlock-avoidance scheme. Deadlocks take place about twice per month and the operator must

What are the advantages of Linked allocation? The benefits are a. No external fragmentation b. Size of the file does not require to be declared

Q. Data transfer between two processes? Communication: Data transfer between two processes is essential for some time. Both processes are on the one computer or on different

Hierarchical paging Single way is to use a two-level paging algorithm, in which the page table itself is also paged. A logical address is separated into a page number and a pag

As mentioned earlier, the game engine will be used as the base of developing the Go game for the Android. This includes improving logic of the game, design good graphics and optim

How does an operating system make multiprogramming possible by using single processor?