Implementation of locks, Operating System

Assignment Help:

How could we implement locks? No matter how we choose to implement them, we must have some hardware support. One possibility for implementing locks on a uniprocessor machine is is to disable interrupts when testing/setting locks. With interrupts disabled on a single processor machine, the processor cannot switch processes, and so we can guarantee that only the active process will have access to the shared data. Another option would be to make use of atomic operations, such as test and set. This type of operation (which usually corresponds to a single atomic assembly instruction) behaves as if it used the following C function, atomically:

int test_and_set(int x) // let x be strictly either 0 or 1.
{
if (x) { return 1; } else { x=1; return 0; }
}

All this needs to be implemented atomically, in hardware. Using this type of atomic operation, one could implement thread lock(l) simply as while test_and_set(l) {

; // do nothing
} // spinlock version of thread_lock()
and thread unlock(l) simply as
l = 0; // we need this to be an atomic clear (or assign) instruction

The assembly instruction test and set can bemade to be atomic acrossmultiple processors. An equivalent option would be an atomic compare and swap assembly instruction. These low-level hardware solutions are then built up into high-level functions, either built into the languages, or in libraries. In general, do not implement your own locking functions, but rather use functions from a tested library. Getting things right can be tricky, and your own solution is also likely to be non-portable.


Related Discussions:- Implementation of locks

Activities of an operating system, Q. What are the five main activities of ...

Q. What are the five main activities of an operating system in regard to process management? Answer: a. The creation as well as deletion of both user and system processes

What inference does recovery in distributed systems, Q. Consider a distrib...

Q. Consider a distributed system with two sites A and B. Consider whether site A can distinguish among the following: a. B goes down. b. The link between A and B goes down.

Find the number of drives in the jukebox, Q. In a disk jukebox what would b...

Q. In a disk jukebox what would be the result of having more open files than the number of drives in the jukebox? Answer: Two bad results could result. One likelihood is star

Why do organisations need a structure, Problem 1: (a) The grouping of o...

Problem 1: (a) The grouping of organisational activities (usually into ‘departments' or larger ‘divisions') can be done in different ways. Outline 7 criteria which can be used

What is a sequential file, What is a sequential file? A file that is re...

What is a sequential file? A file that is read one record or block or parameter at a time in order, based on a tape model of a file.

Demand-paging system, Consider a demand-paging system with the following ti...

Consider a demand-paging system with the following time-measured utilizations: CPU utilization: 10%, Paging disk: 98%, Other I/O devices: 5%. What does this imply? How to improv

Can indefinite blocking take place, Consider the subsequent resource-alloca...

Consider the subsequent resource-allocation policy. Requests as well as releases for resources are allowed at any time. If a request for resources can't be satisfied because the re

Read-write locks, Consider a large web-based database. In some sense, Googl...

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

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