GOPI: A Generic Object Platform Infrastructure

1
GOPI A Generic Object Platform Infrastructure

• Geoff Coulson
• Distributed Multimedia Research Group,
  Department of Computing, Lancaster University
• geoff_at_comp.lancs.ac.uk

2
Overview

• micro-ORB based, modular middleware for QoS
  demanding, soft real-time/ multimedia
  applications
• provides QoS in a standard OS environment
• signal, request/ reply, stream, pipeline
  interaction
• static and dynamic QoS management
• low level API supports various application level
  computational models (e.g. CORBA, RM-ODP)

Personality
Personality
GOPI
3
Influences

• RM-ODP computational model
• signals underpin both operations and flows
• explicit binding
• QoS specification
• engineering principles (cf. Sumo and others)
• adaptive/ fair share based soft real-time support
• application specific protocols/ flexible protocol
  stacks
• low level resource managers for tsaps, threads,
  buffers
• non-multiplexed, upcall based system structure
• efficiency minimise copies, context switches
  user threads

4
The CORBA personality

• IDL extensions for signals, flows, QoS groups

5
Programmers view of binding

• specialise QoS/ QoSM classes for each ASP/app...
• use standard binding class...
• establish binding...

6
GOPI modules
stubs, language binding

• minimal dependencies
• each module is a separate library
• most modules are internallyconfigurable also

bind
comm
(msg)
thread
(base)
7
Bind irefs and binding topology

• irefs comprise
• iref identifier
• profiles (ASP, default QoS specification)
• handler (only meaningful in creator address
  space)
• role and interaction type information
• each iref has both customer and provider role
• INOUT for operational bindings IN/ OUT for
  others
• allows rich binding topologies

INOUT/INOUT
INOUT/INOUT
OUT/IN
OUT/IN
OUT/IN
8
Comm

• framework to support stacks of application
  specific protocols (ASPs)
• currently supported TCPASP, UDPASP, FIFOASP,
  FRAG, SHMEM, NATP, LOCAL, tIIOP
• per-ASP QoS specification and mapping
• ASP at level n maps to
• QoS specification of ASP level n-1
• or to generic thread/ buffer/ tsap resource
  managers at bottomof stack

9
Comms ASP framework

• standard ASP interface
• int asp_listen(Profile pf, InterType
  intertype)int asp_connect(Profile pf,
  InterType intertype)int asp_accept(Profile pf,
  int listening_sap)int asp_close(int sap)
• int asp_relisten(int sap, Profile pf)int
  asp_reconnect(int sap, Profile pf)int
  asp_reaccept(int sap, Profile pf)int
  asp_hdrsize(int sap)int asp_flipqos(CharSeq
  cs_qos)int asp_send(int sap, Buffer
  buf)int asp_receive(int sap, Buffer
  outbuf)int asp_call(int sap, Buffer inbuf,
  Buffer outbuf)
• first 7 operations are used by the binding
  protocol
• do per-ASP QoS mapping/ resource (re)allocation

10
NATP - an example ASP

• network audio transport protocol by N.
  Parlavantzas does adaptive audio playout (ala vat
  etc.)
• considerably more programmable than vat!
• stacked on top of FRAG/ UDP
• configured by QoS parameters (e.g.
  samples_per_pkt, pkt_interval, initial_delay,
  adaptation_algorithm)
• interacts directly with audio device but can
  track or synchronise with other streams via
  handler upcalls
• direct connection concept

11
Binding creation (bind/ comm)

• Iref bbind(Iref cust, prov CharSeq qos
  Handler qos_h)
• supports third party binding
• QoS is an opaque data structure
• interpreted and mapped by ASP in underlying comm
  module
• ltaspgt_qosbuild(CharSeq qos, t1 p1, t2 p2, ...)
• b is used to control the binding (pause, reneg,
  unbind)
• qos_h receives QoS reports from underlying ASP

QoS2
QoS3
...
...
transport connection
12
Thread

• fast, standalone user level thread package with
  per-thread timers and timed semaphores etc.
• thread pools
• support for pluggable application scheduling
  contexts (ASCs)
• int asc_init(void)bool asc_admit(Thread t,
  CharSeq params)void asc_deschedule(Thread
  t)Thread asc_schedule(void)
  Thread asc_expel(int thread_id)
• encapsulate scheduling policy, run queue,
  admission test, VP(s)
• non-preemptive, preemptive, time sliced options
• EDF and priority based scheduling in default ASC

13
Non multiplexed data path

• each binding has dedicated tsap and thread
• combination upcall/ downcall scheme
• receive side data path (send side analogous)
• 1. a deferred interrupt handler runs in thread
  modules context switch code sends msg to
  bindings thread
• uses a callback framework supported by thread
  module
• 2. when scheduled, the bindings thread downcalls
  the ASPs receive() routine
• 3. the bindings thread then upcalls the irefs
  handler
• binding QoS determines ordering of receive()
  calls

14
Performance

• tested on single SPARCstation 5/ SunOS 5.5
• simple char arrays no complex marshalling
• Orbix 2.3MT oneway ops used for Orbix streams
• GOPI program used FRAG ASP, not IIOP

15
Future work

• group ASPs and corresponding binding protocol
  extensions (ongoing)
• re-implementation or wrapping in C
• thread resource management with VPs and kernel
  lottery scheduling
• runtime configuration using Reflective Python
• http//www.comp.lancs.ac.uk/computing/users/geoff
  /GOPI/

16
Scope for reflection

• module level (replacement)
• base alternative OS wrappers, list, stack,
  hashtable classes
• thread alternate resource mgmt
• msg alternate buffer management
• bind RSVP based, ReTINA based, have new
  alongside the old, e.g. for multicast

17
More scope for reflection

• intra-module level
• thread replace/ tailor scheduler configure
  number of VPs, priority levels ...
• msg buffer pool size high/ low water marks
• comm add new ASPs configure IO notification or
  polled IO select() on read or read/write
• bind policy for caching management connections
  for INOUTs thread-per-invocation/ single thread/
  thread-pool policy for operation demux (e.g.
  hash table type)
• general
• intercept inter module calls for performance
  monitoring
• switch on/off debugging info...

18
Conclusions

• micro-ORB middleware to support soft real-time/
  multimedia applications
• supports request/ reply interaction and streams
• provide QoS in standard OS environment through
  policy-free QoS specification/ resource mgmt
• small, modular and efficient implementation
• more information
• http//www.comp.lancs.ac.uk/computing/users/geoff/
  GOPI/