Skip to main content

Difference between spin locks and semaphores--Some Notes

up vote
down voteaccepted
Both manage a limited resource. I'll first describe difference between binary semaphore (mutex) and spin lock.
Spin locks perform a busy wait - i.e. it keeps running loop(In turn heavy CPU usage example is
in Reactor usage of AsyncTaskExecutors):
while (try_acquire_resource ());
...
release();
It performs very lightweight locking/unlocking but if the locking thread will be preempted by other which will try to access the same resouce the second one will simply try to acquitre resource untill it run out of it CPU quanta.
On the other hand mutex behave more like:
if (!try_lock()) {
    add_to_waiting_queue ();
    wait();
}
...
process *p = get_next_process_from_waiting_queue ();
p->wakeUp ();
Hence if the thread will try to acquire blocked resource it will be suspended till it will be avaible for it. Locking/unlocking is much more heavy but the waiting is 'free' and 'fair'.
Semaphore is a lock that is allowed to be used multiple (known from initialization) number of times - for example 3 threads are allowed to simultainusly hold the resource but no more. It is used for example in producer/consumer problem or in general in queues:
P(resources_sem)
resource = resources.pop()
...
resources.push(resources)
V(resources_sem)

Comments

  1. Disha21 January 2016 at 02:06

    Can you please explain the difference between waiting threads and suspended threads?
    I mean both are waiting in the end..we are not able to use them?

    ReplyDelete
    Replies
    1. Abhisar21 January 2016 at 19:31

      It doesn't mean much of a difference.The only thing in depending on programming language there's a little variance. Wait basically means your thread is active and actively using your CPU cycles waiting on some conditions.Suspended means your thread context is saved and currently your thread is dormant and not burning off CPU cycles.

      Delete

Post a Comment

Popular posts from this blog

Introduction to GIT and GITHUB

In this series I would be covering the basic operation of  GIT so that even a new comer can easily feel comfortable with the terminologies and usage of git system. The first post is just a brief introduction that will help you clarify the questions raising about this new thing. What is a Git? Git is simply a software that helps you manage your source code.That means each change that you make to a source code is recorded in its history.So it can also be called as Source Code managemnt system. To use git for a particular project all you need is to initialize the current project folder so that it will be tacked by the git system.I will show it in further documents about how to do it. Every Git working directory(or you can say your project folder) is a full-fledged repository with complete history and full version tracking capabilities, not dependent on network access or a central server. What is GitHub ? In layman terms you can think of
2 comments
Read more

PyCache - A simple, yet extensible in memory Python caching library/framework

https://github.com/Abhisar/PyCache A Small library/extensible framework that aims to solve the problem of needing a cache while coding small/medium scale python projects without depending on 3rd party cache systems. PyCache This library aims to solve the problem of generic object(Python) caching without depending on 3rd party caching systems like Memcached or Redis for cases where it isn't really required. Library has been written in such a way it can be extensible by following standards through implementations of Python Abstract Base Classes. pycache folder  : It has all the base classes. One that ensures ensures all cache schemes follow a similar implemntation i.e https://github.com/Abhisar/PyCache/blob/master/pycache/BaseCache.py  and Other one is for the Objects to be cacheable they have to subclass this Base class  https://github.com/Abhisar/PyCache/blob/master/pycache/BaseCacheable.py CacheImplenations folder : This folder contains different caching schemes. Cur
Post a Comment
Read more