<< Chapter < Page Chapter >> Page >

Which are more powerful, messages or monitors?

Message systems vary along several dimensions:

  • Relationship between mailboxes and processes:
    • One mailbox per process, use process name in send and receive (simple but restrictive) [RC4000].
    • No strict mailbox-process association, use mailbox name (can have multiple mailboxes perprocess, can pass mailboxes from process to process, but trickier to implement) [Unix].
  • Extent of buffering:
    • Buffering (more efficient for large transfers when sender and receiver run at varying speeds).
    • None -- rendezvous protocols (simple, OK for call-return type communication, know that message was received).
  • Conditional vs. unconditional ops:
    • Unconditional receive: return message if mailbox is not empty, otherwise wait until message arrives.
    • Conditional receive: return message if mailbox is not empty, otherwise return special "empty" value.
    • Unconditional send: wait until mailbox has space.
    • Conditional send: return "full" if no space in mailbox (message is discarded).

What happens with rendezvous protocols and conditional operations?

  • Additional forms of waiting:
    • Almost all systems allow many processes to wait on the same mailbox at the same time. Messages get passed to processes in order.
    • A few systems allow each process to wait on several mailboxes at once. The process gets the first message to arrive on any of the mailboxes. Thisis actually quite useful (give Caesar as an example).
  • Constraints on what gets passed in messages:
    • None: just a stream of bytes (Unix pipes).
    • Enforce message boundaries (send and receive in same chunks).
    • Protected objects (e.g. a token for a mailbox).

How would the following systems fall into the above classifications?

  • Condition variables
  • Unix pipes

Classical ipc problems

The dining philosophers problem

A classical problem from Dijkstra

  • 5 philosophers sitting at a round table
  • Each has a plate of spaghetti
  • There is a fork between each two
  • Need two forks to eat

What algorithm do you use for access to the shared resource (the forks)?

  • The obvious solution (pick up right; pick up left) deadlocks.
  • Big lock around everything serializes.
  • Good code in the book.

The purpose of mentioning the Dining Philosophers problem without giving the solution is to give a feel of what coordinationproblems are like. The book gives others as well. We are skipping these (again this material would be covered in a sequel course).

The readers and writers problem

  • Two classes of processes.
    • Readers, which can work concurrently.
    • Writers, which need exclusive access.
  • Must prevent 2 writers from being concurrent.
  • Must prevent a reader and a writer from being concurrent.
  • Must permit readers to be concurrent when no writer is active.
  • Perhaps want fairness (e.g., freedom from starvation).
  • Variants
  • Writer-priority readers/writers.
  • Reader-priority readers/writers.

Quite useful in multiprocessor operating systems and database systems. The “easy way out” is to treat all processes as writers inwhich case the problem reduces to mutual exclusion (P and V). The disadvantage of the easy way out is that you give up reader concurrency. Again for moreinformation see the web page referenced above.

Questions & Answers

how can chip be made from sand
Eke Reply
is this allso about nanoscale material
Almas
are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
where is the latest information on a no technology how can I find it
William
currently
William
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Operating systems' conversation and receive update notifications?

Ask