Cool: Kernel Support for ObjectOriented Environments

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Cool Kernel Support for Object-Oriented
Environments

• Presented by Li Zhao

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Effort on distribution before Cool

• Until early 1990s
• bolting on distribution to existing language
  system.
• Drawback of this approach
• As the language and system are strongly coupled,
  all the layers of object management are typically
  redefined and implemented for each programming
  language that you want to install on the
  underlying OS.
• Thus what was required
• A more efficient approach providing a
  distributed platform that supports a generic
  object model allowing existing object-oriented
  languages to be layered above.

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Cool Introduction

• What is Cool
• Chorus Object-Oriented Layer
• Goals
• Provide an efficient object-oriented support
  layer built on top of the Chorus Micro-Kernel.
• Provide an generic object support platform that
  support multiple object-oriented language

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Cool Architecture
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Cool Architecture (continue)

• Cool Base
• System Level layer
• Has the interface of a set of system calls and
  extends the Chorus Micro-Kernel abstraction
• Acts as a Micro-Kernel for object-oriented system
• Is built of four main functional components
• Cool sub-system object provides the cool system
  interface
• Cool class manager responsible for managing
  class representation
• Cool mapper
• responsible for managing the mapping between
  object representation in virtual memory, and the
  secondary storage representation
• Cool activity monitor used to manage
  communication directed to objects that are in
  transit
• Cool Generic Run-time
• Cool run time system specializes the system
  interface to support a specific object model.

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Cool Abstract

• Cool System
• A set of abstraction designed to enhance those
  provided by the chorus Nucleus
• Actor
• Cool exists as a set of system actors that
  provide an object oriented interface above the
  Chorus Nucleus
• each actor implements a subset of the overall
  system functionality
• Actors communicate via the Chorus IPC mechanism
  and collectively provide the system interface
• Context
• Is an actor
• Provides an address space in which object exist
  and models a traditional address space
• Each context can support a variable number of
  virtual memory regions, sparsely allocated and
  each backed by a secondary storage entity managed
  by an external memory mapper

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Cool object
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Inter-object communication

• Object invocation
• Objects created with a global attribute are
  assigned a port for communication and use this as
  the end-point for messages. Messages, are
  delivered to the target object.
• Object migration
• Unmapping the objects segment from its source
  context
• Transmitting its descriptor and
• Mapping its segment and insert its descriptor in
  the target context list.
• Object group
• Cool also allows objects to be grouped according
  to communication categories.
• This allows a group of objects to be denoted as a
  single endpoint and allow messages to be
  delivered to all objects in a group.
• The decision to migrate an object is driven by
  the requirement to optimize a particular
  invocation.(Chorus System The Cool Approach)

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Persistence

• Object Persistence
• Cool allows system developers to detach objects
  from the context they reside in and move them to
  backing store returning a persistent object
  identifier. At later point, such objects can be
  re-mapped from store to a context. But
• Unable to perform any form of reference
  conversion, because object reference are not
  tracked by Cool.
• Context Persistence
• The entire context can be stored, including
  objects within that context.
• Insures all virtual memory references remain
  valid.

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The cool C object

• Each C object that will be used as a Cool
  object is defined from a base class Cool.
• COOL C objects are compiled and then partially
  linked at a static, user defined address. Such
  Objects are left in executable files(with the
  same name as the class) but are not fully linked.
• The COOL system then uses the COOL mapper to map
  in the correct text and data segment. At this
  point the COOL/C object is dynamically linked
  with the COOL system interface itself.

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COOL/C Object (continue)

• A number of additions have been made to the C
  object model to deal with the mapping of C to
  Cool.
• Relocatable pointers
• Used to allow the C run-time to effectively
  relocate dynamic structrues when their parent
  object is migrated.
• Members
• Members allows us to dynamically build tree
  structures of related objects and to migrate the
  entire tree from its root object.
• It is necessary for the programmer to provide
  hints on which objects belong to related
  structures.
• Active objects
• To provide a degree of parallelism, objects may
  be created as active, with a lightwight Chorus
  thread beginning execution at a designated entry
  point in that object.

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Conclusion

• The goal of cool project was to be able to
  support a large spectrum of object-oriented
  run-time.
• The Cool layer provides address space management
  and basic functionality for object management.
• Object migration consists of changing the mapping
  of the object components.

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Thank you!!!Any Question???