.ac.uk!dcl-cs!pr
Subject:  comp.os.chorus Frequently Asked Questions (FAQ)
Revision: 1.19
Last-Modified: 1996/04/03
Summary: This posting contains a list of Frequently Asked Questions 
         (and their answers) about the CHORUS microkernel technology.
Supersedes: <chorus-faq_825678680@comp.lancs.ac.uk>
Nntp-Posting-Host: columbine.comp.lancs.ac.uk
Cc: pr@comp.lancs.ac.uk
Posting-Frequency: monthly
Date: Wed, 3 Apr 1996 09:12:24 GMT
Maintainer: <chorus-adm@comp.lancs.ac.uk> "Philippe Robin"
Archive-Name: chorus-faq
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Xref: senator-bedfellow.mit.edu comp.os.chorus:291 news.answers:68574 comp.answers:17952


What's new?

Availability of a binary evaluation version of CHORUS/COOL ORB (Chorus' 
implementation of OMG-CORBA specifications) at URL:"http://www.chorus.com". 


...

        Table of Contents
        =================

1. General Information
    1.1. Organization and Availability of this FAQ
    1.2. What's New?
    1.3. What is CHORUS?
    1.4. How to Contact Chorus Systems?
2. Documentation
    2.1. Documentation Available through Anonymous FTP
    2.2. Papers on CHORUS
    2.3. Other references
    2.4. Press references
3. Chorus Product Offering
    3.1. Overview
    3.2. Offering for Universities
4. CHORUS Microkernel
    4.1. General
    4.2. Supported Microprocessors
    4.3. Porting on various platforms
    4.4. Scheduling and real-time
    4.5. CHORUS on Transputers
    4.6. Comparison with other OS
    4.7. Perfomances
    4.8. Object Oriented issues
5. OS Personalities
    5.1. OS personalities available on top of CHORUS
    5.2. CHORUS/MiX V.3.2
    --------------

1. General Information
   ===================
1.1. Organization and Availability of this FAQ
     -----------------------------------------
  This FAQ contains informations related to the CHORUS operating system,
description of the products and contacts. It will be progressively 
updated according to the discussions held in this newsgroup and the 
evolution of the products.

  It is posted once a month in the following newsgroups:<<comp.os.chorus, 
news.answers, comp.answers >>. Copies of the FAQ can also be obtained by 
e-mail by sending a request to "chorus-adm@comp.lancs.ac.uk". A hypertext
version of the FAQ is available on the World Wide Web at the following 
URL:"http://www.comp.lancs.ac.uk/computing/users/pr/www/chorus/faq.html"

  You can make any comments, suggestions or contributions to this 
FAQ by sending an e-mail to "chorus-adm@comp.lancs.ac.uk" or 
"pr@comp.lancs.ac.uk" or by discussions in the newsgroup.

1.2. What's New?
     -----------
  Availability of a binary evaluation version of CHORUS/COOL ORB (Chorus' 
implementation of OMG-CORBA specifications) at URL:"http://www.chorus.com". 

1.3. What is CHORUS?
     --------------
  CHORUS is a family of open microkernel-based operating system
components to meet advanced distributed computing needs in areas such
as telecommunications, internetworking, embedded systems, realtime,
"mainframe UNIX", supercomputing and high availability. The CHORUS/MiX
multiserver implementations of UNIX allow to dynamically integrate
part or all of standard UNIX functionalities and services in the above
application areas.

  CHORUS is designed, developed and marketed by Chorus Systems.


1.4. How to Contact Chorus Systems
     -----------------------------
     North America:
.Chorus Systems Inc.
.1999 South Bascom Avenue, Suite 400
.Campbell, CA 95008
.United States
.Phone: +1 (408) 879-4100
.Fax:   +1 (408) 879-4102
.Voice Mail:  +1 (408) 291 8832
.Email: info@chorus.com

     Europe:
.Chorus systemes SA
.6 avenue Gustave Eiffel
.F-78182 St Quentin-en-Yvelines Cedex
.France                        
.Phone: +33 (1) 30 64 82 00        
.Fax:   +33 (1) 30 57 00 66        
.Email: info@chorus.fr         

     Asia Pacific:
.Chorus Systems KK
.Mitsutake Building Ikejiri, 8F
.3-22-4 Ikejiri, Setagaya Ku
.Tokyo 154
.Japan
.Phone: +81 (3) 5430-1131
.Fax:   +81 (3) 5430-1133
.Email: info-ap@chorus.com

2. Documentation
   =============
2.1. Documentation Available through Anonymous FTP
     ---------------------------------------------
  There are several technical reports on CHORUS available via anonymous
FTP from Chorus systemes, France: ftp.chorus.fr [192.33.15.3],
directory pub/chorus-reports (see the file "index" for an overview).
A set of slides on CHORUS is also available in the directory 
"pub/chorus-slides", documents CS-TR-92-64 (PostScript, versions 1-up 
and 2-up). The latest version is the document CS-TR-92-64.4, Apr 94.

  Product Data Sheets are available (in ascii or PostScript format) in
the directory "pub/chorus-datasheets".

  Those reports are available through the World Wide Web at Chorus 
systemes: "ftp://ftp.chorus.fr/pub" or from the Web server at the 
URL:"http://www.chorus.com".

2.2. Papers on CHORUS
     ----------------
[Bricker, 1991] A. Bricker, M. Gien, M. Guillemont, J. Lipkis, D. Orr and
M. Rozier, "A new look at micro-kernel-based UNIX operating systems:
Lessons in performance and compatibility". Proc. of the EurOpen Spring'91 
Conference, Tromsoe, Norway, 20-24 May 1991.
Chorus Systems Technical Report CS-TR-91-7

[Coulson, 1994] Coulson G., and G.S. Blair. "Microkernel Support for 
Continuous Media in Distributed Systems". Computer Networks and ISDN
Systems, Special Issue on Multimedia, 1994; also available as internal
report MPG-93-04, Computing Dept., Lancaster University.

[Gaultier, 1994] O. Gautier and Y. Metais. "Mise en Place d'une Plateforme
CHORUS, Conception et Implementation d'un Ordonnanceur a Echeance au Sein 
du Noyau Chorus". Memoire CNAM, Paris, March 1994.

CS/TR-94-82.1 "CHORUS Kernel v3 r5 for T425/T805 Connection Manager and
..Aserver Library" (Internal Report)

CS/TR-94-81.1 "CHORUS Kernel v3 r5 for T425/T805 Host Server User's
..Manual, Aserver Guide" (Internal Report)

2.3. Other references
     ----------------
[Bradley, 1993] J Bradley Chen and Brian N Bershad
"The Impact of Operating System Structure on Memory System Performance",
ACM SIGOPS Dec. '93

[Coulouris, 1994] G. Coulouris, J. Dollimore and T. Kindberg. "Distributed
Systems, Concepts and Design", Addison-Wesley, second edition, 1994.

[Douglis et al., 1992] Douglis, F., Kaashoek, M.F., and Tanenbaum,
A.S.: "A Comparison of Two Distributed Systems: Amoeba and Sprite,"
Computing Systems, vol. 4, Fall 1991 (sic).

[Dean, 1992] R. Dean and F. Armand. "Data Movement in Kernelized Systems".
Proceedings of the USENIX Workshop on Micro-Kernels and Other Kernel 
Architectures, pp. 243-261, April 1992.

[Tanenbaum, 1992]  Andrew S. Tanenbaum: "Modern Operating Systems",
Prentice-Hall, 1992.

[Tanenbaum, 1994] Andrew S. Tanenbaum, "Distributed Operating Systems", 
Prentice-Hall, ISBN 0-13-219908-4

2.4. Press references
     ----------------
BYTE, Jan 94 issue:
      - "Small Kernels Hit it Big" (by Peter Varhol, p. 119, 6 pages), and
      - "The Chorus Microkernel" (by Dick Pountain, p. 131, 4 pages)
    (a color reprint of these articles is available upon request
    from Chorus Systems.)

BYTE, Feb 95 issue:
      - "Novell's Campaign" (by Jon Udell, p. 43, 11 pages)
    CHORUS is mentioned in this article as being the basis for
    the microkernel underpinning the UnixWare and NetWare personalities.

BYTE, Mar 95 issue:
      - "Europe's Chip Challenge" (by Dick Pountain, p. 19, 5 pages)
    CHORUS is mentioned in this article on the CEC's Open Microprocessor
    Initiative (OMI) as the microkernel being used and enhanced within
    various OMI projects.

3. Chorus Product Offering
   =======================
3.1. Overview
     --------
  All CHORUS products, except CHORUS/Fusion, are source products.

  The CHORUS Nucleus is a realtime distributed microkernel; current
release is v3 r5.3 (Mar 95).

  CHORUS/Simulator is a port of the CHORUS microkernel on top of UNIX;
current release is v3 r5.2 (May 94). It runs as a UNIX process, e.g.
under SunOS 4.1 or Solaris 2.3 on a Sun SPARCstation, and allows one 
to develop and test applications using the microkernel's API.

  CHORUS/MiX V.4 is a distributed multi-server implementation of 
UNIX SVR4.0 on top of the CHORUS microkernel; current release is 
r3.1 (Jun 95). E.g. on a 386/486 PC/AT, it offers binary compatibility 
with native SVR4.0v4. MiX V.4 requires a Novell/USG SVR4.0 sources license.

  CHORUS/Fusion for SCO Open Systems Software is a multi-server
implementation of SCO UNIX and extends it with realtime functionality 
(POSIX 1003.1b and .1c, i.e.  the former .4 and .4a interfaces) and 
clustering functionality.  CHORUS/Fusion is developed and marketed 
jointly by SCO and Chorus as a binary product on Intel-based PC's.
The current release is r2.0 (Sept 95).

  CHORUS/COOL is a distributed programming environment for object-oriented
applications. CHORUS/COOL supports the dynamic creation of C++ objects,
these objects can be invoked, using C++ mechanism in a system wide
transparent way. Objects can migrate, and remain persistent unless
explicitly deleted.  The programming model used is based on the Object
Management Group's architecture (OMG). Current release: v2 r3.0 (Aug 95).

  CHORUS/COOL-ORB is an OMG-CORBA compliant Object Request Broker. It is
available for CHORUS/Fusion, CHORUS/ClassiX, CHORUS/MiX V.4, SCO UNIX,
SunOS 4.1 and Windows 3.1. Current release: r2.0 (Aug 95).

  CHORUS/ClassiX is host-target cross-development environment for
C++ or C written applications, named C_actors. C_actors can be loaded,
unloaded and debugged dynamically from the host (e.g. SPARCstation/SunOS) 
on the target (e.g. ix86 PC/AT), interconnected via Ethernet. 
C_actor applications can interoperate with UNIX on the host
through TCP/IP sockets and NFS. On the target, there is only the
CHORUS/Nucleus microkernel and the CHORUS/C_actor subsystem but
no CHORUS/MiX UNIX System V subsystem.
CHORUS/ClassiX is available for i386/i486/Pentium (PC/AT), mc68040
(MVME167), mc68360 (QUADS) Micro-SPARC-1/-2 (FORCE CPU-3CE/-5CE,
SPARCclassic, SPARCstation 5, SPARCengine 5) and T425/T805/T9000
(SGS-Thomson INMOS boards).  Current release: r2.2 (Jun 95).



3.2. Offering for Universities
     -------------------------
  Chorus Systems has special programs for universities. More information 
on offerings, conditions, etc is available via ftp on "ftp.chorus.fr" in 
the following ASCII files
    - pub/README
    - pub/academic/README
    - pub/academic/offerings

  If you have questions, you may contact Didier.Irlande@chorus.fr.


4. CHORUS Microkernel
   ==================
4.1. General
     -------
    * What is a microkernel?
    A "microkernel" is an operating system with only the essential services, 
    such as interprocess communication, short-term scheduling, and memory 
    management.  It basically provides the process abstraction and a means 
    for processes to communicate. It is designed to be portable between 
    computer architectures, using high-level languages such as C or C++ and
    reducing the machine-dependant component to a minimal bottom layer.
    The microkernel appears as a layer between the hardware layer and a 
    layer consisting of system components called 'subsystems'.
    Their size can vary from about 10Kb to several hundred kilobytes 
    of executable code and static data.

    * Synchronisation primitives offered to CHORUS threads?
    The CHORUS microkernel (v3 r5.x) offers the following synchronisation
    primitives:
.- mutexes
.- (counting) sempahores
.- spin locks (supervisor applications only)
.- mini messages (supervisor applications only)

    Other synchronisation primitives such as condition variables and
    reader/writer locks can be built on top of those basic primitives.

    * Do CHORUS threads support specific data?
    Yes. The microkernel supports so-called "software registers".
    Each thread has two software registers which are systematically 
    saved/restored by the microkernel upon a thread context switch. 
    The software registers can be read/written through threadStoreR(K) 
    and threadLoad(K) system calls.
    A software register typically contains a pointer to a per-thread
    private data area. Via software registers, one can implement e.g.
    a per-thread value of "errno".

    * Distributed synchronization service on top of the CHORUS microkernel?
    This work is part of a PhD thesis undertaken by Stephane Eranian 
    <eranian@chorus.fr> implementing distributed synchronization service on 
    top of the CHORUS microkernel. It implements pure mutex (no mr/sw).
    The synchronization is achieved using a token-based algorithm through
    a server. Its main role is to manage token creation, deletion and sharing 
    among sets of clients. For more information contact S. Eranian.

    * Initialization of the context of an actor created with the actorCreate(K)
    system call?

    To create an actor in CHORUS using actorCreate(K), the actor address
    space must be empty (i.e. does not include any valid memory region). 
    If you want to "fork" an actor, i.e. the new actor's code and data is
    a copy of the main actor's code and data.

    In order perform address space duplication, you can use the rgnDup(K) 
    service, just after having created the actor (and before having created
    new regions: this operation is only valid on an empty address space).

    Before invoking rgnDup(K), you must specify for each region how the region
    will be "duplicated": map (sharing), copy or not duplicated at all.
    In order to do this, you have to get the list of your regions
    (rgnStat(K)), and set the inheritance flags using rgnSetInherit(K).

    Note: an alternative to the rgnSetInherit/rgnDup scheme is to treat each 
    region individually, using rgnMapFromActor(K) for shared regions,
    and rgnInitFromActor(K) for copied regions.

    * Encryption mechanisms in CHORUS IPC?
    CHORUS IPC does not provide any "encryption" mechanisms. Such mechanisms
    can be implemented by applications.

4.2. Supported Microprocessors
     -------------------------
  Various versions of the CHORUS microkernel have been ported to a
variety of microprocessors, either by Chorus Systems or by its 
clients:

    - i386/i486/Pentium (various PC/ATs)
    - mc68030/mc68360/mc68040 (MVME147S, QUADS, MVME167S)
    - mc88k
    - SPARC (SPARCstation SLC, SPARCstation Classic, SPARC CPU-3CE)
    - transputer T425/T805/T9000
    - R3000/R4000 (Sony 3410)
    - PA-RISC (HP 9000/834 and 9000/720)
    - YMP (Cray YMP)

4.3. Porting on various platforms
     ----------------------------
    * Chorus on Macintosh?
    The INT (Institut National des Telecommunications, Evry, France) has
    ported the v3 r3 version of the CHORUS microkernel to a Macintosh II CX
    (mc68030-based). CHORUS and MacOS coexist and cooperate on the same
    hardware.
    The paper "Cohabitation and Cooperation of Chorus and MacOS", by
    Christian Bac and Edmond Garnier, was presented at the Usenix Symposium
    on Microkernels and Other Kernel Architectures in Sep 93 in San Diego.
    You can find the paper in the proceedings. It is available from 
    ftp.int-evry.fr:/pub/systeme.

    In the same directory you will also find another paper on the same
    subject: "ChorusToolbox : MacOS running on top of Chorus", by Christian
    Bac and Hong Quang Nguyen from INT. This paper was presented at SUUG'94
    in April 94 in Moscow.

    * CHORUS on transputers?
    Archipel, Chorus and SGS/Thomson Inmos have ported the CHORUS
    microkernel and the CHORUS/MiX V.3.2 subsystem (SVR3.2 compatible) to
    T425 and T805 transputers. This was done in the context of the Esprit
    project "Harmony" (EC-funded R&D). Initially, a T9000 port was planned to
    be available by now. Due to a delay in the availability of the T9000,
    the CHORUS port (which is underway now), has shifted as well.
      Inmos and Chorus have been working together in order to assure that
    CHORUS/MiX (i.e. UNIX) will run in an optimal manner on the T9000.

    * CHORUS on 64-bit architecture?
    CHORUS has been ported to DEC's Alpha, Cray Research's YMP and 
    MIPS' R4000.

    * Port of CHORUS on HP-PA?
    On December 1st Jon Inouye <jinouye@cse.ogi.edu> wrote:

        Prof. Jonathan Walpole supervised a port of the CHORUS v3.3 
        nucleus to the Hewlett-Packard 9000/834 workstation from late 
        1990 to mid-1991. This was part of a funded research project 
        to evaluate the CHORUS operating system with respect to the 
        Hewlett-Packard PA-RISC architecture. The nucleus did not 
        support any disk/network drivers and performed all console/
        keyboard I/O though IODC (PROM) routines. A CHORUS/MiX V.3.2 
        Process Manager (PM) port was partially completed to the point 
        where UNIX shells and certain system calls were supported ... 
        but not a UNIX file system.

        Since then, I have been porting Chorus/MiX V.3.2 (with the v3.4 
        nucleus) to the HP 9000/720. Since I am performing this port in 
        my spare time it is not progressing very fast. The v3.4 nucleus 
        runs along with a serial driver. It lacks other device drivers, 
        FP emulation support (though basic FP operations are supported) 
        and still uses the old HP-UX PDIR structure rather than the more 
        recent HPT. The Ethernet driver is still being debugged as is an 
.ancient version of the MiX V.3.2 PM. The port is being used for 
        virtual memory experiments.

        Both ports use a considerable amount (over 40,000 lines combined) 
        of HP-UX source code for the assembly language utilities, boot up, 
        I/O initialization, and device drivers. The 834 port uses a Tut 
        (HP-UX 2.0 modified to run Mach 2.0) base and the 720 port uses 
        a HP-UX 8.0 base. For this reason, we have not been able to release 
        anything because of all the legal implications ... HP, Chorus, USL 
        copyrights.

        The evaluation is available as a series of OGI technical reports 
        which can be obtained via anonymous ftp from cse.ogi.edu (129.95.20.2)
        in the directory /pub/tech-reports or via the URL:
.    "http://www.cse.ogi.edu/DISC/projects/pa-chorus/pa-chorus.html".

    * Are PCI-bus devices supported on ix86?
    PCI devices, like video and IDE, whose I/O mode is compliant with ISA,
    are supported; they are just seen as ISA adapters.
      PCI devices which are not ISA compliant (e.g. the SCSI controller
    and/or the Ethernet controller on some COMPAQs) are not supported;
    supporting them would require modifications in the driver code (and
    possibly also in the CHORUS microkernel code).

4.4. Scheduling and real-time
     ------------------------
    * Scheduling mechanisms and scheduling policies
    The CHORUS microkernel makes a distinction between scheduling mechanism
    and scheduling policies. The core scheduler within the microkernel does
    pure preemptive scheduling (SCHED_FIFO in POSIX RT terms). On top of
    that, different scheduling policies can be implemented in the form of
    scheduling classes; each class communicates with the core scheduler and
    can make its own scheduling decisions within that class based upon
    attributes (priorities, deadlines, etc) and behaviour (time-slicing,
    SCHED_RR, ...).
      Today, 4 scheduling classes are provided: a default class and the 3
    UNIX SVR4 classes (SVR4_TS, SVR4_RT and SVR4_SYS). Work is in progress
    for additional classes (deadline, fair-share, etc) cf the work done 
    by Olivier Gaultier and Olivier Metais at CNAM Paris on the implementation
    of an EDF (Earliest Deadline First) policy in the CHORUS kernel.

    * Relative cost of context switch between user and supervisor threads?
    User threads/actors have their own address spaces, and are protected
    from other user address actors.
    Supervisor threads/actors all share the supervisor address space,
    each supervisor actor has its own "slot" in the supervisor address
    space.

    For comparison, let's take:
        [U] a context switch between 2 user threads in different user 
            actors,
        [S] a context switch between 2 supervisor threads in different
            supervisor actors

    Unlike [U], [S] does not require the saving/restoring of the memory
    context, so [S] is less costly. For the CHORUS/Nucleus v3 r5.2 on 
    a i486/50MHz, the ratio [U]/[S] is 1.57.

    * How to measure Interrupt latency?
    The easiest way is to connect an interrupt handler to a hardware timer.
    As soon as the handler is activated, the handler will measure the current
    time and then wake-up a thread, e.g. by doing a V on a semaphore. The
    thread, when returning form its P operation on the same semaphore, will
    also measure the current time. The difference between these 2 time
    measurements is the latency.

    If you are using CHORUS/ClassiX or CHORUS/MiX V.4, you should take a
    look at one of the example applications in the tutorial, named ILD
    (Interrupt Latency Demo) which does exactly this work.


4.5. CHORUS on Transputers
     ---------------------
    * On transputers, how to communicate from CHORUS to UNIX (SunOS)?
    There is no standard way to do this with CHORUS. This is the kind of 
    things CHORUS/MiX is there for. 
    Specific to transputer, you can use emulated links. On your 
    workstation run a daemon, the "Aserver", which comunicate
    with your b300 box. Together they emulate transputer virtual links 
    over TCP/IP. These links can then be used by transputer and Unix 
    applications to communicate. For details on how to do that, see 
    the sections on the Aserver in the CHORUS documentation (CS/TR-94-82.1
    and CS/TR-94-81.1).

    * Use of the INMOS RTL for the C-toolchain to work with sockets?
    [Answer on Dec. 6, 1994 from B. Wipfel <raw@unislc.slc.unisys.com>]:

      Guessing that you want to make socket calls from one of your actors,
    and have the B300 handle them in the normal way, the trouble is that
    the transputer implementation of CHORUS uses AServer, not IServer. 
    Since AServer communication is encapsulated in IServer MEGA_PACKETS, 
    the B300 never gets to see any of the socket packets and passes 
    everything to the host. 

    A real option is to write a new AServer server to provide your socket 
    service. In this case, all communication will go to the host, and it 
    will make the socket calls on behalf of your actor in the target system. 
    The B300 wouldn't be involved, other than maintaining normal AServer 
    communication with the host. This is kind of a shame, since the B300 
    has the necessary functionality.

    A last option might be to use a second root link. Wire up two links 
    from the B300 to your transputer network. Boot the network via one of 
    the links. Configure the second link as a network "EDGE". Have your 
    actor connect to the edge link with one of the AServer routines; 
    something like cmLinkOpen("/dev/raw/00") ? Once the link is open, and 
    you have the channel pointers, it might be possible to attach the 
    socket library channels to these channels. You'll need to do 
    communication via CHORUS' channel I/O routines however. 

    * If we have made ourselves a sockgateway process, configured in 
    the .cfs file as:
. ....
.interface(input fromhost, output tohost,
..  input formChorus,
..  output toChorus);

    Where do we connect the input and outputs ?
    [Answer on Nov. 25, 1994 from N. Stephen <stephen@osf.org>]:

      I don't know what release you might have, but look up the #device 
    primitive in the build tool users manual. This primitive allows you 
    to attach native transputer processes' channels (which normally 
    control devices) to the CHORUS world, and does all the necessary 
    wiring so that these channels are accessible from the connection 
    manager. There may also be an example of this being done in one 
    of the tutorials, if you have them with your release - the CHORUS 
    Nucleus Tutorial (2), mixing CHORUS and Native transputer code.

4.6. Comparison with other OS
     ------------------------
    * differences between Mach and CHORUS?
    There are a lot of similarities between the concepts of the 
    CHORUS v3 r5 microkernel and the Mach 3.0 microkernel: IPC, threads, 
    memory management. 

    Some of the differences are:

    ------------------------------------------
    Feature                     Mach    CHORUS
    ------------------------------------------
    Supervisor actors/tasks     no      yes
    Device drivers out of uK    no      yes
    Global object (port) names  no      yes
    Typed messages              yes     no
    Realtime                    no?     yes
    Sender port                 no      yes
    Send-once                   yes     no
    RPC                         no?     yes
    Reliable IPC                yes     no
    Port group (destination)    no      yes
    Scheduling classes          ?       yes
    (Counting) semaphores       no      yes
    Condition variables         yes     no
    Support for non-VM machines no?     yes
    ------------------------------------------

    See also the reference [Dean, 92] (cf. section 2.3)
    for more elements of comparison between the two kernels.

4.7. Performances
     ------------
    * Is there any system for performance analysis?
    As far as the CHORUS microkernel applications ("actors") are 
    concerned, the CHORUS/Profiler and the CHORUS benchmarks can be 
    used.
    The CHORUS/Profiler allows one to obtain and display symbolic
    call-graph profile data for actors (similar to UNIX' gprof(1)):
    callers, calllees, absolute and relative time spent in different
    procedures within one actor. Actors are to be compiled with the 
    -p option.  The profiler consists of a supervisor actor (PROF) 
    plus 2 CHORUS/MiX utilities.  Profiling be can enabled/disabled 
    dynamically using the CHORUS/MiX utility profctl(1).  profctl(1) 
    stores the raw profiling data in a UNIX file, which can then be 
    exploited by the report generator profrpg(1) in order to produce 
    a human-readable profile report. See ftp.chorus.fr:/pub/chorus-
    datasheets/Profiler_v3_r4.{ascii,ps.Z}.
    CHORUS benchmarks allow you to get performance figures for 
    individual microkernel system calls. For some system calls, like 
    ipcSend(K), you get performance figures for different cases/parameters 
    (small/medium/big message sizes). These basic figures can also help 
    you to analyse and tune the performance of your microkernel applications.

    In the context of the ESPRIT project Ouverture, Alcatel, Siemens and
    Chorus have designed and implemented so-called hooks for monitoring 
    and debugging in the CHORUS microkernel. These hooks are a clean set 
    of new microkernel system calls which allow monitoring and debugging 
    tools (e.g., PATOC, PARTAMOS) to be informed about the occurrence of 
    events they're interested in (context switch, message arrival, thread
    creation, etc). They will be available in a future CHORUS product
    release.

    PATOC is a graphical tool (Motif-based) that allows to monitor 
    applications running on CHORUS. It is event based and is able 
    to display its information is various forms (diagrams, bar-charts 
    etc). PATOC is not a product but rather a working prototype. 

4.8. Object Oriented Issues
     ----------------------
    * How is CHORUS Object-Oriented?
    The major part (>90%) of the CHORUS microkernel is written in C++. 
    OO techniques are used in the implementation of the microkernel, but the
    API exported by the microkernel is a traditional procedure call based
    interface (like UNIX).

5. OS Personalities
   ================
5.1. OS personalities available on top of CHORUS?
     -------------------------------------------
  Chorus Systems has developed the following personalties:

    - SVR4.0
    - SVR3.2
    - SCO ODT 3.0
    - BSD4.3
    - object-oriented (CHORUS/COOL)
    - POSIX real-time (POSIX 1003.1b/.1c, former .4/.4a)

  Others have developed, or are developing, personalities for SVR4.2 MP,
UNICOS, MacOS, CHILL, ESTEREL, TINA DPE, and a number of (proprietary) 
real-time OSs.

5.2. CHORUS/MiX V.3.2
     ----------------

    * What is the link between a u_thread and a kernel thread?
    A u_thread is an abstraction, created by the CHORUS/MiX V.3.2
    subsystem, on top of the microkernel threads (like a UNIX process 
    is created on top of a CHORUS actor).  Each u_thread is mapped 1-1 
    to a microkernel thread. A u_thread has some UNIX-specific attributes, 
    like signal context, which is managed at the CHORUS/MiX subsystem 
    level, as an added value w.r.t. a microkernel thread.

    * Which synchronisation primitives are offered to u_threads?
    Sempahores and mutexes.

    * Do u_threads support Thread Specific Data?
    Yes, through the threadsafe C library (c_threadPrivate(3CT),
    c_getPrivate(3CT)). These functions are in fact built on top of the
    software registers described for the kernel threads (cf 4.1).

    * How are u_threads scheduled?
    By the microkernel, just like any other thread.
    If one want to implement N user level threads on top of 1 kernel 
    thread, he need a user level scheduler in some kind of run-time 
    library (just like an Ada run-time schedules multiple Ada tasks 
    within one Ada program).

    * Is there a way to calculate the size of a u_thread stack?
    For dynamic calculation, the best approach is probably to fill 
    the stack you allocate with a specific pattern, and then at 
    run-time (or at thread termination) control which part of the 
    stack still contains the pattern. This allows to calculate 
    which part of the initial stack has (not) been used.

    To detect a stack overflow, the classical approach is to surround 
    the stack by some chunks of memory that are mapped read-only.

    * Is it better to put the thread stack in the data segment or in 
    the heap area?
    The only advantage of putting it on the heap is that the corresponding
    memory can be allocated (and freed) dynamically, according to the
    application's run-time behaviour and needs. If you allocate it as 
    data, the corresponding memory is always allocated, even if your 
    thread doesn't exist yet/anymore.

    * What are the differences between an u_thread and a c_thread?
    The c_threadXxx(3CT) interface is a library, built upon the 
    u_threadXxx(2C) interface, and is inspired by early drafts of 
    the POSIX pthreads interface (POSIX 1003.4a, later renamed to 
    .1c). It offers a higher level interface than u_threadXxx(2C), 
    e.g.:

.- when creating a c_thread the library creates the stack 
.  for you, while for a u_thread you have to allocate the 
.  stack yourself,
.- there is a routine allowing one c_thread to wait for the 
.  termination of another c_thread (c_threadJoin),
.- there are routines to allocate and access per c_thread 
.  private global data.

