Sep 26, 1988 - tives, scheduling mechan/sms, .... dispatching and ... operating systems [8]include a monolithic, kernel, process hierarchy,functional hierarchy,.
Report
No.
UILU-ENG-88-1720
UIUCDCS-R-88-1415
TAPESTRY
Principal
Technica/Report
No.
Process
TTR88-4
Management
and
in Multiprocessor Using
Investigators
Exception
Operating
Object-Oriented
Handling Systems
Design
Vincent
Roy Campbell and Daniel Reed
Techniques
Russo
Gary Johnston Roy Campbell September
26, 1988
TAPESTRY
DEPARTMENT UNIVERSITY
OF COMPUTER OF ILLINOIS
SCIENCE
AT URBANA-CHAMPAIGN
• URBANA,
ILLINOIS
61801-2987
Contents 1
Introduction
1
1.1
Related
Research
1.2
Structuring
2
The
Choices
8
Processes
.................................
an Operating Class
System
3 Using
Class
Hierarchies
...........
4
Hierarchy
6 7
3.1
Memory
Management
.......................
3.2 3.3
Process Implementation and Context ProcessContxiners .................................
3.4 3.5
Exception The CPU
Handling ................................ ProcessContxiner Subclass
3.6
Hardware
Exceptions
...............................
, ....... Switching
......................
................
7 8 9 9 i0 ii
4
Semaphores
12
5
Schedulers
13
6
Summary
15
References
17
Process
Management
and Exception
in Multiprocessor Using
Operating
Object-Oriented
Design
Vincent
Handling
Systems Techniques*
Russo
Gary
Johnston
Roy
Campbell
September
26, 1988
Abstract The progr_=rrrn;n_ of the interrupt
h_n,]1;n_
mechanisms,
process
switching
tives, scheduling mechan/sms, and synchronization primitives of an operating for a mnltiprocessor require both efficient code in order to support the needs
primisystem of high-
performance or real-time applications and careful organization to facilitate maintenance. Although many advantages have been claimed for object-oriented class hierarchical languages and their corresponding design methodologies, the application of these techniques to the design of the primitives within an operating system has not been widely demonstrated. To investigate the role of class hierarchical design in systems programming, the authors have constructed the CTw/ces multiprocessor operating system architecture using the C++ progr_mm_ language. During the implementation, it was found that many operating system design concerns can be represented advantageously using a class hierarchical approach, including: the separation of mechanism and policy; the organization of an operating system into layers, each of which represents an abstract machine; and the notions of process and exception management. In this paper, we discuss strategy
1
an implementation
of the low-level
by which we developed
primitives
of this system
and
outline
the
our solution.
Introduction
The tion
Choices [i] [2] operating system architecture to the design problems of operating systems.
is organized Applications
as a class for which
hierarchical Choices has
solubeen
•This work was supported in part by NASA under grant number NSG14T1 and by ATtzT METIIONET.
designed
include
itoring
numerical
systems,
research
and
controllers
was motivated
spedalized
memory
and
be easily
extended
gration,
and
ing system
applications
to organize
implemented this
that
the
family
abstnac_
minimize cations
overhead
that
design
shared
memory.
within
the
process
Any
dais
A major
the
hierarchy,
are
switching
motivation
The C++ programming
Choices.
Therefore,
class
complex
Mesa
or AdaS).
xMultimax
systems
designer
may
hierarchy
define
conclasses
objects
be specialized
application many
into
in
for a
in order
different
a "general
to
appli-
purpose _
nor uses.
across
the and
interprocess
the applications
memory.
as objects,
Choices network.
have
the
design
language
and
communication is supported
support 2
by
for networked
Processes
implementations
exclusively
is also an investigation to either
classes
of Encore
that
already
within
Computer
class
are
defined
that
reduce
hierarchical
of complete
supports
features
object-oriented
to an existing
has system
Choices
that
objectoperating
in the implementation
of the appropriateness
which
adding
if the
implementation
[7] was used
in a language
language
we discuss
was to determine
for the
as opposed
is a trademark
memory
Choices
classes
supports
for efficient between
virtual
research
be used
programming
In this paper,
required
modeled
this _-'search
hierarchies,
more
requires
techniques
1
systems.
primitive
dedicated
hier-
system
Multimax.
The
may
designed
class
service
of these
Choices
and
system
system.
hierarchy
features
for particular
overheads.
systems.
operating
Thus,
neither
in shared
for this
could
the
Encore
system
of a particular with
memory
and
of system
An operating
operating
mi-
operat-
selection
services
operating
subclasses within
efficiency.
virtual
approach
and
Concrete
communication
oriented
in 8 complete
a custom
associated
objects
extends
context
to build
or the needs
virtual
runs on the
systems
process
uses objects
of a family
classes
operating conventional
problems.
The
Classes
the application
exploit
Choices
example
for
of heterogeneous
current the
The
systems
reconfiguration,
specialized
mon-
networks.
operating
a predefined
of classes.
in order
requests.
on persistent
multiprocessors
hardware.
hardware-independent
and to improve
system
operations
components
to provide
concept
a hierarchy
any overheads
Choices via
through
example,
offers
currently
the
switched
Similarly,
that
ground-based
coUections
balancing,
to both
architecture supports
environment
but avoids
operating
parallel
implementations.
hardware
on large
management.
extended
and
and packet
load
a Ukernel"
solutions
Choices
to application
Choices
specific
facilitate
primitive
respond
particular
be easily
architecture
or spedalize
talus
resource with
control
multiprocessor
For
dynamic
on particular
and
with
Choices
provides choose
CPU
cannot
circuit
of building
multiprocessors.
applications
flight
applications
to manage
heterogeneous
this kernel
concurrent
real-time
networked
provides
services;
The
difficulties
high-performance,
cannot
embedded
for high-speed
by the
shared
archies
computations,
support
of implementprogramming
language
programming process
of
or using
features
(e.g.,
dispatching
and
a
Corporation.
2Messsse-oziented kernels like the V Kernel [3], Accent I4], Amoeba [5], and MICROS [6] build specific communication schemes into the lowest levels of the kernel. For example, some systems implement a few ways of providing _virtusl _ messages like "fetch on access, m However, these systems are not easy to adapt to support other approaches such as "send process on read" or '_.mote procedure caU on execute." aAds is s trademark of the Department of Defense (Ads Joint Program Office).
2
execution, exception handling, processcontext The
classes
provide
the primitives
application-specific
systems
1.1
Research
Related
The
from
which
switching,
scheduling,
higher-level
layers
and
of the
synchronization.
operating
system
or
are constructed.
organization of an operating system is a dimcult task. Many
differentapproaches to
structuring operating systems have evolved in response to advances in hardware technology and improvements
in software ensineering techniques. Approaches
to the structuring of
operating systems [8]include a monolithic, kernel, process hierarchy,functional hierarchy, and object-orientedcapabilitystructure. Many
simple microprocessor and some early batch operating systems are structured using
the monolithic approach: as a large program
that invokes user programs
as _subroutines."
These applications Ureturn" by requesting operating system servicein the form of a system call,by terminating, or by being preempted Many which
current
application
such
as its
often
introduce
the
the
often
notion
of a CPU
abstractions
among
and
applications
multiple
of operating
the
are organized
on an Uabstract
of a concurrent
provided
though
is large
execute
by a hardware interrupt.
like UNIX
use by other
the majority
Even
systems
programs
concurrent
sharing
minimal; the
operating
CPU" and
process
executes
details
hardware the
Typically,
software
a /_eene[
that hides I/O
to support
applications.
system
its
using
abstraction
the
to build
can benefit
provided
However, may
in a kernel
should,
from structuring.
system
may
The
objects Both
for
small
by definition,
Layered
operating
large
that
and
systems
system
manner.
operating
into
process
most
is
exploiting
kernel
system
that
the
processes
within
kernel
a system
the
system
operating
considers
The interaction
it of
of such an object-oriented
processes
systems
of the
desirable
lack
of today's
the
asynchronism
solution major
internal
of separating
through
it structures
is a practical
are suitable
of any
property
communicating
because to many
operating
because
has the
of a kernel
applied
Instead, within
services.
One example
up well
important
contents
has been
system
to organizing
scale
approach
is very
layers.
processes
required
portability,
[12].
approaches do not
solutions
and
an operating
and
of capabilities. 432 system
[9] and
Each layer is built as the abstractions and
various
into
THE
it
the hierarchy.
to structuring
applications
a set of cooperating model
the
the
to a minimum,
notably
maintainability
[11]. Concurrent
approach
iAPX
By separating
levels
includes
but
Layering systems
of the kernel
of the kernel
be kept
systems,
improved
to organize hierarchy
as a network
The operating
layer. offers
at different
is the Intel
the monolithic
cooperating
easy
capability
is organized
an operating intuitive
functions
of objects
system
structure. The
always
objec_-o_ented
operating
layering
as a j_anction_
access
as a collection the
by the previous system,
it is not
be organized
permits
by the kernel.
software
an operating
Kernel's
that
software
outside
in
of the real CPU
interface.
Venus [i0], structure an operating system as a series of layers, or levels. a collection of concurrent processes and software modules that exploit enhancements
approach
kernel. in an
to structuring
operating
systems
[13][14][15][z6]. The major layer
di_culty
in which
processes
of a particular by lower disk
since
memory
memory
planning
memory
paging
caused
such
networks.
However,
organized
into layers.)
To summarize, by providing
operating
a machine processes,
hierarchy,
or by representing
system Each
as objects. approach
dif[erent
1.2
approach.
without
standard
concerns
that
would
like
programming
and some
objects
concurrent
processes.
The class inheritance
The between language
engineering class
that
A process Class
within
hierarchies that
do classes
been
previous
among
operating
complexity. derived
by a
approaches
with
of
include
class
existing
from
one layer
may
coercions and
structure
access
objects
references
modular
operating
are
used
as
collection8 or contain
in other
layers.
to these also
objects have
the
programming.
a operating
system
systems. Reuse is gained from the that care is used in the construction
4
In this
are
define
programming
within
major
object-oriented
that
may
object-oriented
of the
organize
approaches.
Choices, layers
of such
hierarchies.
others allow
design
hierarchies
Within and
reuse
to
The
construction
expression
and
design
hierarchies
a kernel
reuse
to the the
by class
functions
code
operating system layers, and across with class and inheritance provided
permit
of a system.
code
encourages
Hierarchies and
also represent
within
type and
Class
is permitted
to build
and upward
approach
with
have
organization
or kernel.
system
defined
advantages
hierarchical
used
the they
layering
of a layer
are
dependencies,
of an
inheritance
but easily
use
and
only
that
the
provide
mechanism
manner.
Not
to the
internals may
Using
improve
methodology
issue
inheritance
of objects;
in a structured
the
will
techniques,
to emphasize
to structure
this
not be expressed
the design
is an orthogonal
a means
software
could
System
penalty.
design
these
are
approach.
of class hierarchies
believe
system
we describe
systems
We
objects
into a functional
or coping
could
distinguish
to reduce
to represent
the
abstractions
that
in designing
helps
machine
But, virtual
of shsrin 8 of a CPU
of simplicity
to implementations
the
problem
(unless
the
paging
store.
with
of processes,
and
systems,
can be used
the details
into layers
internals
memory
approach
by hiding
services,
we shall
difficult
the
provided
as a backing
lack structure
in terms
Operatin_g
a performance
operating
support
section,
of the applications
systems.
that hides
object-oriented
is a study
systems
We
next
an
of operating
section,
In the
hierarchical,
kernel
mechanisms,
lead
disk
capabilities
organized
system
memory virtual
be coordinated
capability
since
the
or functions
the
use the must
is determining
structuring
in virtual than
are the most
been
has merits
Structuring
Choices
design
the
Each approach sometimes
must
networks
have
by structuring
may
our own class
arbitrary
independent
concurrent
level
buffers
dependencies
systems
and
For example,
by a lower
mechanism
kernels
on the processes
The object-oriented
cyclic
somehow
rely
dependencies
system.
by such
arbitrary
only
use for I/O
Such circular
system
be implemented
may
is necessary.
drivers
of an operating
the problems
operating
should
be provided
the disk
management.
the layers
layered
each layer
should
the
that
building
or functions
Since
careful
drivers
mechanism the
layer.
layers,
device
with
layer,
use of a of the
subclasses. By building class hierarchies in which methods are through subclassing, much code can be shared between classes. Layered
operating
functions
and utilities
are
mutual
exclusion
hash tables, in several
layers
form
algorithms
and
to apply
them
classes
Families
repeated
data structures
of useful
to the
needs
specific
within
of operating
operating
also
portion
of reuse simplifies and application. The class
hierarchical
operating
system
concepts,
offer many
possibilities
the family
the
parent
also encourages
of systems
is 8uided
and
hierarchy.
The
hierarchy
view
of how the
the possible
with
function
addition,
subclassing
to be modified
without
All machine operating classes
system class
instances
policies
specifies
of the
class
system
archy.
so that
(Not
be reused, the
_fan
out"
In later management
implement similar
only do classes including
and
support (2-7)
of this paper exception
and
overall
view
of a Choices
form
machine and
by
the
mod-
structure
designer
with
a
It classifies
com-
of a parent
class,
for Choices,
of the system. operating
class
to specify
In
system
encapsulated that
may
refines
design
within
class
from a common
operating policies
hierarchy ancestor
by a hierarchy
Overall,
on
the implementaversions,
the
An
be used
to specify
particular
possible, induced
management),
set of subclasses.
we have
is hier-
may
also
constrmned
reuse.
the use of this methodology Choices.
table
are
(its methods)
in the hierarchy.) code
page
dec/s/ons
be specialized
5
This
for a target
systems
as a potential
but the structure
to encourage
with many
similar.
function.
(e.g.,
Wherever
can
are
the function
A concrete
are used
we will discuss within
these
An abstraction
as a class
8 and
the
are used in our system
of the classes
handling
des/gn
protocol
abstraction. reuse,
classes
system. meclmn_,r_
and
subclasses the
these
Customization
system
part
subclasses.
classes
abstract
instantiating
reuse.
systems
subclassin
a good
implemented
sub-hierarchies
code reuse
to be small
parts
Abstract
Concrete
that
constructed
and its concrete
by
to achieve
system
behavior
of a system.
[17] [18]. In the class hierarchy
rest of the
are
and
for a particular hardware or of the class can all share a
provides
of a specific
schedulers)
decision
a general
class.
abstractions.
or mechanisms
the
operating (e.g.,
Design
tion of an abstract
behavior
chansing
then
if they
by learning
can be inferred
the
class
of an operating
to be mastered
depemienc_es,
in Choices.
abstroct
need permits
aided
to their function;
of a subclass
only the top few classes
class
components
respect
be used
the
subclassing
customization.
of a family
of a system
the layers
of code
of operating
by the
ponents
may
lists,
of the definition
may be defined
a "version" of that class The different versions
induced conceptual
queues,
to represent
and
system
layer.
ification
class
system,
Common
schedulers
throughout classes
of the family
approach
and
allow the reuse
generic
through
the customization
reuse.
incrementally
For example,
processes,
data structures
within
of the implementation
layers.
Classes
of an operating
component
code
by defini'ng
different subclasses each implementing a particular application's requirements. large
layer.
a specific
systems
system
for
d_erent
semaphores, and
is enhanced
objects
opportunities within
primitives, algorithms
reuse
to produce
of some
many
the application
of abstract
of code
offer
often
including
implementation This
systems
specialized
to design
process
Choices
Base
Classes
Class
Methods c'tor
d'tor
_MemoryRsnge
c'tor
d'tor
_Process
c'tor
d'tor
_ProcessConts/ner
c'tor
_Exception
c'tor
Object
reserve
release
physicaiAddress
d'tor
add
remove
-
d'tor
raise
-
Legend Symbol method
Meaning of method.
Definition
method
Redefinition Subdass
Table
2
The
Before
going
into
the
Base
Class
details
of the
hierarchy
is appropriate.
Choices
class
hierarchy
&re shown
in a Choices This
about
the
executed Class
system.
is usus/ly
memory
ProcessContaine_
To aid lowest provides Germ
an "ides/ized" Objects
subclasses
of generic
the
h&rdw&re
system
include
memory
4The %'irtual" machine copy of the actual hardware
by
major
classes,
a brief
classes
in the
subclass
the
(i.e.,
redefines
information machine
to execute.
added
to provide
in this
to and
overview first
and
of the
level
adds
necess&ry
registers) Processes
removed
for Process
that
design
of the
methods
to execute
and
information
&re scheduled
from
execution
for mansgin
for use in the
classes and
that
define
physical
management,
&re grouped
encapsulates
h&rdw&re &rchitecture
defined
exception,
Each
it expects
by being
objects
the meclmnisrrs8
computer.
1.
information
in which system
It is a set of objects
provides
Hierarchy.
and
ProcessContainers.
and
scheduling.
Class
basis for exception handling, inc.luding traps and interrupts. The usually causes Exception-specific movement of Processes between
in portability,
layer.
Choices
exception
of the
is represented state
is specialized
Ezception provides the raising of an Exception ProcessContainers."
and
Some
in Table
A Process
a Choices
in the
MemoryRange provides the base for storage management Instances of class Process are the basic units of execution
the processor
virtual within
Classes
process
class
defined for class Object. Class in a Choices operating system.
method.
method.
Hierarchy
Choices
it.
or inherited
Undefined
1: Major
Choices
of method.
the
to the
into
major
rest
Germ
interfaces processor
exception
for specific to the manasement
Germ
is the
dependencies
and
layers
in the system.
4 The
the physics/resources architectures
h&rdw&re
mechmxisms.
The
h&rdw&re
of the
8 and maintaining
layers.
&re instances
memory
Intermediate , schedulin
of the of
management, layers
8 and naming.
in the The
provided to the higher layers of the system by the Germ objects is not a virtual m in the IBM VM/370 [16] operating system, but rather an idealized _chitecture.
6
Kernel
is the
highest
to applications. particular
hardware
appropriate
layer
in the system.
A complete
operating
of the system,
for the
It defines
system
objects
applications
that
belonging
are
system
are implemented oriented
thus is ideal
example,
classes,
design
whose
loading
class
stack
thus
system
while
are
imposing
the functions
memory
management
sections,
run-time handling,
it supports
assembly
in C ++. It is easy
registers).
itself
(for
However, of methods
even
class
and
to the lowest
hierarchical
even of low-
levels
of
object-oriented
overhead.
we will describe
of interrupt
a few small
implementations
implementation
because
object-
overhead
in the language
unit
with
synchronization,
It implements
directly
impossible
objects
Individual
hierarchy
runtime
are, of course,
not be implemented
the object-oriented
negligible
and
minimal
machine-dependent
C++ was chosen
for parallelism portable.
things
and Kernel
the class
and
system for the
system.
augment
with
to achieve
and
mostly
layers,
semantics There
by the
appropriate
operating
is efficient
could
in order
by the
support
programming.
functionality
preserving
hierarchy.
language
provided
objects
to the middle
can further
including
hierarchy
pointers
routines
In the following ment
The class
C++ to assembler
assembly
level
C++. and
for operating
routines
to interface
the
using
programming
language
these
components,
of Germ
supported
applications that run on top of the new system their own classes. All operating
the interface
consists
in more
process
detail
some
dispatching,
of the classes
context
which
switching,
imple-
scheduling,
and synchronization.
3
Processes
Choices
supports
lightweight,
the
concept
independent
of a computation
parallel
application may use multiple lelism. A single one of these class.
Each instance
share
memory
such
of the
Process
to be useful
Memory
A complete
discussion
order to discuss Memory
of the
represents
management
and basis
Choices
description
process
management
MemoeyRange
SA more complete
to those
described
to allow and
an independent mechanisms
efficient
the context
process switching
large
number
in [3] [13] and
of
[19]. An
concurrency and paralof the Choices Process flow of control
described
below.
migration,
the
effort between
that
can
In order amount
for
of in-
two processes
Management
this paper, s A general
stract
class
throu8 h the memory
an abstraction
similar
of a potentially
communicating processes to achieve processes is represented by an instance
formation kept on a per-process is minimized.
3.1
processes
composed
of the
management
and
in Choices
class as root. description
memory
management
way memory context
is implemented The classes
is contained
in [1].
system
is managed
switching
is, however,
the
scope
necessary
of in
in Choices.
by a hierarchy
in this hierarchy
is beyond
of classes
support
virtual
with
the
memory,
abthe
sharing
of memory,
a contiguous
and memory
range
to represent
the
class
Space.
A Space
cess.
The class
Domain
class
Choices
code,
within
this
Domain.
initial
processor
The
a Process
switching Process
Context
minimum
context
represented
can
be
within
associated
real
may be locked only
resident Locking
sired. in the
is currently
switching
overhead.
to be locked
as addressable in resident
can optimize
privileged
shared
Spaces
locked
as addressable and
to exclude Germ
access
and
the
as Spaces Domain,
arguments
scheduling
virtual
to
parameters,
processor
incurs
from
in non-privileged
process
system
switch
the
Domain
processes
with
code,
context
switchin
memory
and 8
to be and
In addition,
the
a Space
that
addresses
loadin 8 overhead, processes
e as de-
by runnin 8 the processes protection
of the
even though
a Space
from
are implemented
the
within
a stack,
fast
and real-time
ePlns MMU cache flnshin 8 overhead, if the old and new Domains differ.
8
in
is necessary.
to a process
memory Thus,
within
to be validated
register
protected
object
execute
matches
Locking
applications
mode.
which
accesses
memory.
handlers
are stored
between
addresses
only
contents
Process
switching
its Domain,
8 the
it can remain
of a Choices
dispatched
as resident.
other
settin
that
to switch
virtual
of interrupt and
by each
Processes
in physical
and register
class is used by the process
context
ability
A context
memory
state
copies
being
within
as resident
by all Processes.
by all Domains, memory
the
corresponding
still be protected
of the
with between
of s Space
the performance
may
state
the
processor
no memory
contained
memory
causes
Usually,
by an initial
manipulate
Since an executing
a Space
pases
registers
8 require
memory
memory.
pointer),
is maintained
of the Process
Spaces
the
either
Spaces.
are represented
of the Process
is lowest
executing,
processin
Such processes
The Kernel
if the Domain
by locking
stack
a CPU's
real-time
stack
or stack
the
method
overhead
by the various
achieved
resident
since
and
supervisory
to reload
memory
be accomplished
is parameterized
Domains,
by storing
The dispatch
switching
the processor
Interrupt data
A small
their
can
be accessed
during
list common
its virtual
and
counter
may
into the
8.
is recorded
object.
Domain
alter
and dispatchin
code in Choices
a common in which
for Processes
preemption.
object.
for a process program
that
is
by a Pro-
Switching
specifies data,
example
It is subclassed
is consulted
which
Context
that
important
memory
processes
Domains
unlnitialized
(for example,
of a process
order to handie
a Domain
constructor
of virtual
represents
is subclassed
addressable
of Spaces.
between
different
most
memory
of a process
and
data,
The
state
preemption
state
within
or through
initialized
Methods
handie
view
Domain
Implementation
executable
and
in the
class
MemoryRange
The
of virtual
for the a_regation
the complete
references
implies.
in a system. a range
Sharin 8 of memory
Process
the process.
of memory
of Spaces
Domains
Process
Each
list
of a MemoryRange
as the name
to represent
is provided
decisions.
shared
3.2
kinds
represents
The
An instance
addresses,
is used
which
manasement throush
different SpaceList
by a Process.
protection.
of memory
unprivileged as sets
81obally may
be
processes.
of such Spaces.
Processesand ProcessContsiners Methods
Class Object _Process
.... dispatch
_P_ocessContsiner _1SinsleProcessContsiner H_CPU ilFIFOSchedu]er H _RoundRob/nSehedu/e_
add add add add _
Table
3.3
2: Process
chanKeDomaln
getSchedulerInfo
setSchedulerInfo
remove
is_.mpty
-
remove
_Emp£v
-
_mo_ remove _-mo_e
_ iaEmptv 1
-
and ProcessContainer
Base
Classes.
ProcessContainers
Primitives instances name
for scheduling, blocking of the Pro_ssContainer
implies,
involve
is a container
transferring
in Choices
Subclasses Some
are de_ed
and defines or not).
Processes
LIFO,
ProcessContainers implement
queues
queuing
contain add
or priority
of processes
dispatching Table
disciplines
a single
algorithms
2 shows
Processes
and isEmpty these
methods,
(e.g.,
dling.
The
condition.
Exception The
system
"run queues"
class
defines class
HardwareExceptions architecture.
ily by an executing Processes
way for a process
in Choices
the base the
classes
method
has subclasses
for a HardwareException
of the underlying cause
3 shows
Exception
The raise method interrupt.
are introduced Table
process.
to be moved to suspend
abstraction
and
are used Exceptions
by the
"ready
abstract
of Choices raise
class
is
remove
the container
to add and
that
to intercept
to encapsulate method are
ProcessContainers.
and
remove
refined
may
and
and
and
han-
SoftwareEzception. of a hardware
hardware
exception
Raising
refined
the exception
as a result
objects
be used
exception
correct
to
Scheduling
class
implement
of a SoftwareException
the primary
its own execution.
the
be
operation.
Ezception
which
directly
may
queues"),
HardwareEzception
is called
The raise between
contain.
order.
an operating
Handling
exceptions
whether
for example,
3.4
Low level
they
into the container),
(for testing
await an event or are blocked on a Semaphore in more detail in a later section.
by its subclasses.
of the classes
The ProcessContalner
to store processes that in Choices is discussed
Exception
by using as the in Choices
some
on the Processes
Process.
(for inserting
can redefine
represent
and
in Choices are built A ProcessContainer,
ProcessContalners.
from the container),
Subclasses
in FIFO,
and
impose
to only
the operations
Processes
Scheduling ProcessContahlers.
Processes
of ProcessContainer
(for removing is empty
between
implement
subclasses
abstract
of Processes.
Processes
which
and dispatching processes class and its subclasses.
mechanism
is called
in Choices
whose
an Exception
trap or voluntarmethods
is the only
Exceptions Class
Methods
Object
w
J,Exception _HardwareException _ _Interrupt
Exception
await
ra/se
fixFault
rcl/Se
-
$_DivideByZeroTrap
ra/ae
-
_TimeSUceInterrupt
m/Be
clockTick
l_SoftwareException
ra/se
handler
1_ J,SemaphoreException
J,
handler
processing of the
CPU
subclass
of ProcessContainer,
class,
add method
3: Exception
Handling
ProcessContainer
fits naturally
CPU
-
Table
A special
1 ra/ae
_ J,_MegallnstructionT_ap
The
-
ra/se
_Abort'i_ap
3.5
raise
into this model
each
corresponding
to dispatch
and execute
Base
Classes.
Subclass
CPU,
represents
since
a system
to an actual a Process
an actual
physical
can consist
of more
processor.
on the
The
processor
To effect
the
process
Exception
transfer
must
is raised,
of the
first
the context
stack. These supervisory to hold a single process invokes of any
the
Exception
particular
Exception
CPU
be saved.
handler.
behave
define
the raise
the
exception,
class
after
defines Exceptions
7This executed CPU
and
stack within added
processing
methods
to install
the itself
context
by
the
context
is saved
the
remove
It returns of the
an exception.
the
to another
from the second ProeessContainer two processors at the same time.
method
exe-
When
an
on its supervisory
class
ProcenContainet), added
its
Proceu
a race to
another
10
a minimum
exception
would
where
resulting
in
amount
the the
Process
it
of context The
CPU
an Exception
handling
to remove Proceu
store
Exceptions.
invoking
attempted
CPU
state
of Exceptions
the process.
if a Process exist
CPU,
of hardware
voluntarily If the
the
all classes
resume
initialisation.
(i.e.
from
Not
as the handlers
of the
stack/
Process
CPU.
to save only
by a Process
during
patticulaz
and
the
to the
objects
independent
supervisory
it will immediately
Exception
CPU
is executed
to remove
Process
syneXronously
of any
handler
code
add another
can be raised is created
process
The
preemption.
by raising
to a per-processor
contain
and
because,
redefines
it represents.
to another,
executing
The Exception
by switching usually
way; some
process
of the currently
in a ProcessContainer, this
one
is accomplished
class
stacks exist one per Process object and need only be large enough context. Once the state is saved on this stack, the raise method
process
handlers
from
This
Multi-
than one instance
CPU
method of the CPU class is used by Exceptions to implement CPU the Process for which the CPU has most recently saved a context. cuting
processor.
itself
could being
be
code
was
from
the
removed
executed
by
object's raise method, or voked"
through
more
detail
most
notably
3.6
the
asynchronously
hardware
in the following
sections.
anism
that
traps
for handling
traps
machine
traps
and protection (for example,
Many
a "system
occur
await.
The
occurs,
at which
if they
the
sequence
the
processor
tion object the
and
interrupt
awaited.
and
placed
ready having
queue
When on the
"in-
discussed
and
Exceptions,
in
one
occurs
ready
queue
await
the
of the
the interrupt
and
queue.
This would,
until class
queue" Figure
Process The
Process1 shows
R is running
CPU
object
from
and
the
on
InterruptExcep-
to hold the Process
the
a
InterruptException
occurs,
interrupts,
un-awaited
described
process
awaiting
added
to the
interrupt
then
cause
however,
11
CPU.
class.
The
objects
the require
context
must
have
removed
from
is then
chosen
effect switch
an extra
a
a time-slice
TimeSHceInterrupts
process same
that
For example,
is preempted, Another
to the
above,
interrupts.
TimeSliceIntereupt
ProcessContainer. added
its execution
"ready
is removed
cur-
object.
running
and
the
defines
must
's occurrence.
from
ser-
resumes,
to do with
of the interrupt.
a ProcessContainer W
handler
then
InterruptExceptions
of the
the interrupt
Process
memory program
Trap
to block
adds it to the system's
interrupt
virtual
and
nothing
be resumed. method
R is removed
provides
The
This
explicit
of HardwareException
the occurrence the
and
Process
have
a mech-
of its execution.
types),
by a Process
may
provides
instruction),
trapping
subclass
The raise
hardware
by an instance
the ready
in general,
Before
to the CPU
result
like instruction).
is invoked
Finally
Choices
ProcessContainer
a process
chosen from first method.
added
them,
is handled
not
Process
illegal
and,
process,
Trap class
of various
of the
variable
to the synchronous
awaiting
"SVC"
awaiting
detail.
as an instance
and
In addition
and
context
is awaiting
ProcessContainer.
ProcessContainer process
W
In the figure,
queue
being
are
later.
The
as a direct
faults
the Process
to be missed.
in more
Process
contains
interrupt.
ready
method time
the Process
of events
an
the
of the interrupted
and resumes
page
InterruptEzception
await
are not
the context
Container
call" via
The
subclasses.
may generate
asynchronously
process.
the interrupt saves
are discussed
divide-by-zero
within
new method, be awaited
exceptions
uses of ProcessContainers
major
(for example,
condition Process.
interrupts
executing
a process
(for example, errors
vices the exception or terminates that
rently
of an Exception
Exceptions class has several
access
method Hardware
of semaphores,
The HardwareException includes
raise
mechanism. Combined
in the implementation
Hardware
by the
exception
are
the
CPU,
from
the
can be achieved
by
to a second
context
switch
process over
the
CPU
Ready Queue
Object _er
Raise Message (from hardware)
Queue
Interrupt Object Figure
4
Processing.
Semaphores
In Choices, V, defined
a semaphore [9] is implemented abstractly as follows:
P (Semaphore) count
count
:
count
:= count
( count
if
Wakeup A constructor semaphore.
