Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!agate!saturn!rutgers!mist.math.uoregon.edu!renga@beaver.cs.washington.edu
From: rutgers!mist.math.uoregon.edu!renga@beaver.cs.washington.edu (Renganathan Sundararajan)
Newsgroups: comp.os.research
Subject: THREADS, Light weight processes
Message-ID: <5279@saturn.ucsc.edu>
Date: 26 Oct 88 21:34:51 GMT
Sender: usenet@saturn.ucsc.edu
Organization: University of Oregon, Computer Science.  Eugene OR
Lines: 36
Approved: comp-os-research@jupiter.ucsc.edu


  I came across the notion of  multiple THREADS of control executing 
  within a single address space, when I was reading about MACH, the
  network operating system developed at CMU. I have also heard about
  Light Weight Processs (LWP) but in what context I don't remember. 

  Questions:

    What exactly is a light weight process? 

    Where did the notion of a LWP originate and in what context? 

    Is it the same as a thread?

    Is the sole purpose of a LWP to help switch contexts fast? 

    If a LWP does not own/use any registers and so saving a context
     involves only saving the PC and condition flags, what is great
     about it? (if a process never uses any registers just so 
     that context-switches can be done fast, is there any advantage
     at all? Am I missing something here?)

    Do LWPs and HWPs (H = Heavy - whatever that may mean) co-exist in an OS? 

    Is the notion of a thread unique to MACH or do other os like V use it?

    Are there any machines out there that provide some kind of hardware
    support to LWP switching?

    Any clarifications/references would be appreciated.

  Renganathan
  email: renga@cs.uoregon.edu

  PS: Please email me your response. If there is enough interest, 
  I will summarise.