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

Explain system-wide open-file and per-process open-file, Explain system-wid...

Explain system-wide open-file and per-process open-file The system-wide open-file table have a copy of the FCB of each open file, as well as other information. The per-pr

Identifying parallelism, Identifying parallelism A formal way to identi...

Identifying parallelism A formal way to identify parallelism in an activity is to draw a task dependence graph in a directed graph in which each vertex represents a task to

What is preallocation, What is preallocation? Why do it? Allocating spa...

What is preallocation? Why do it? Allocating space for a file before making the file to allow for expansion. This reserves space for a certain file so that other files can't gr

What are the issues in designing a network, Normal 0 false fa...

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

Explain process states in the unix system, Process States A total of n...

Process States A total of nine states are acknowledged by the UNIX system. They are like as follow: User running                                                   Executing

Write a note on threads, Question 1 Explain (a) tightly coupled systems   ...

Question 1 Explain (a) tightly coupled systems                               (b) Loosely coupled system Question 2 Describe the RPC model Question 3 Write a note o

Explain enhanced second-chance algorithm, Enhanced second-chance algorithm....

Enhanced second-chance algorithm. When we increase the second-chance algorithm by considering both the reference bit and the modify bit as an order pair. We have the following

File system versus swap space, Q. What are the tradeoffs concerned in rerea...

Q. What are the tradeoffs concerned in rereading code pages from the file system versus using swap space to store them? Answer: If codes pages are accumulate in swap space th

What is an i/o subsystem?, What is an I/O subsystem? The control of dev...

What is an I/O subsystem? The control of devices connected to the computer is a main issue while designing operating systems. Since I/O devices differ widely in their function

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