A introduction of generative communication in Linda and Tuple Space

1. GENERATIVE COMMUNICATION
IN LINDA AND OBJECT/TUPLE
SPACE
- Sheng Tian, shengt@gmail.com

2. LINDA: COORDINATION AMONG
PARALLEL PROCESSES THROUGH TUPLE
SPACE.
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3. COMMUNICATE VIA TUPLE SPACE
To send to B, A generates a tuple
out(N, P2, …, Pj)
… and B withdraws it
in(N, P2, …, Pj) 3

4. BASIC OPERATIONS ON THE
TUPLES AND TUPLE SPACES
 Tuple: N, P2, …, Pj
 N is an actual parameter of type name
 P2, …, Pj is a list of parameters each of which may be either an actual or a
formal.
 Insert: out(N, P2, …, Pj)
 Execution of the out() statement results in insertion of the tuple N, P2,
…, Pj into TS
 Blocking read and delete: in(N, P2, …, Pj)
 If some type-consonant tuple whose first component is “N” exists in TS, the
tuple withdraw from TS
 If no matching tuple is available in TS, in() suspends until one is
available
 Blocking read: read(N, P2, …, Pj)
 Same as in() statement but the tuple remains in TS.
 Both in() and read() are logically nondeterminism
 Tuple names are global to a given program’s TS.
 Update tuple: delete and reinsert
 Predicate operations: inp and rdp 4

5. TUPLE SPACES BASICS
OPERATIONS
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6. AGENDA
 Background
 Basic Concepts in Generative Communication
 Distinguishing Properties of Linda
 Case Study
 Discussion
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7. BACKGROUND
 Three basic models of concurrent programming:
 Monitors (shared variables)
 Message passing
 Remote Operations
 Cons
 Partially distributed in space
 Nondistributed in time
 New Model: Generative communication
 Fully distributed in space and time
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8. BASIC CONCEPTS
 Tuple
 A tuple is a fixed-length list containing elements that do not need to
have the same type.
 Tuple/Object Space
 A virtual repository of tuple, shared amongst providers and accessors
of network services, that can be accessed concurrently
 All the participants of the distributed application share an Object
Space.
 Processes communicate among each other using these shared objects –
by updating the state of the objects as and when needed
 Linda
 A model of coordination and communication among several parallel
processes operating upon objects stored in and retrieved from Tuple
Space.
 Generative Communication Model
 Why it is said to be generative? Because, until it is explicitly
withdrawn, the tuple generated by A has an independent existence in
TS.
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9. DISTINGUISHING PROPERTIES (1/2)
 Communication orthogonality
 p1: Space-uncoupling
 A tuple in TS tagged “P” may be input by any number of
address-space-disjoint processes
 p2: Time-uncoupling
 Tuples added to TS by out() remains in TS until it is
removed by in()
 p3: Distributed sharing
 Linda allows j address-space-disjoint processes to share
some variable v by depositing it in TS.
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10. SPACE AND TIME UNCOUPLING
Space-disjoint processes A and B
communicate via TS
Time-disjoint processes C and D. C
terminates before D starts –
Likewise communicate via TS 10

11. DISTINGUISHING PROPERTIES (2/2)
 Free naming
 p4: Support for continuation passing
 Linda allows name-type values to be tuple components and to
be stored in arbitrary data structures in the same way as
values of any other type.
 p5: Structured naming
 Structured naming make TS content-addressable
 e.g.
 The statement
 in(P, i: integer, j:boolean)
 Requests a tuple with name “P”, but it is also possible to
write
 in(P, i:integer, FALSE) and in(P, 2, FALSE)
 It allows in() and read() statements to restrict, and out()
statements to widen, their focus.
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12. CASE STUDY (1/2)
 Database Search Problem
 We are given a file containing a set of search data, a target,
and a routine that computes a numeric score for single datum/
target pair.
 A manager makes a series of out requests to place the
search data in the tuple space, then performs in operations
to retrieve the results generated by workers
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13. CASE STUDY (2/2)
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begin
count = 0
until EOF do
read datum from file
OUT("datum", datum)
count = count + 1
enddo
best = 0.0
for i = 1 to count
IN("score", value)
if value > best then
best = value
endfor
for i = 1 to numworkers
OUT("datum", "stop")
endfor
end
begin
IN("datum", datum)
until datum = "stop"
do
value = compare
(datum, target)
OUT("score",
value)
IN("datum",
datum)
enddo
end
procedure manager procedure worker

14. SPACE BASED ARCHITECTURE
 Object Spaces is a paradigm for development of
distributed computing applications.
 Spaces can be used to achieve scalability through
parallel procesing.
 Objects, when deposited in an Object Space are
passive, i.e., their methods cannot be invoked while
the objects are in the Object Space.
 This paradigm inherently provides mutual exclusion.
 Linda coordination language was developed at Yale.
 Object Spaces is usually called Tuple Spaces since it
contains of tuples unrelated to each others.
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15. IMPLEMENTATIONS OF TUPLE
SPACES
 Java
 Sun’s JavaSpaces
 GigaSpaces
 OpenSpaces
 IBM’s Tspaces
 ActiveSpace
 Jada
 LighTS
 Jxtaspaces for P2P
 GLOBE
 Blitz
 C
 Scientific Computing
Associates’ TCP-Linda
 W.F. Wong’s Simple C-
Linda with Posix Threads
 HTML Page Spaces
 Masatoshi Seki’s Rinda,
part of DistributedRuby
dRuby
 Ruple for Ruby
 p4-Linda
 Python
 PyBrenda in Python
 PyLinda. Linda
implementation in Python
 Matlab: NetWorkSpaces
 Note:
 Ruple use XML documents
instead of tuples
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16. DISCUSSION (1/2)
 Message queue vs. Tuple space
 Messages go from one person to another. Only the intended
recipient of a message gets to see it.
 Tuple Space is a bag with tuple in it. The tuples in TS can
be read and processed by anyone.
 It is possible to force sequencing of messages by including a
time, matching on all messages, then selecting the message
with the earliest time.
 Message passing must has a destination. No matter it's a
single dest or a group. However Tuple space is distributed.
Workers don't know each other.
 Broadcast messages are not like Tuple Space.
 A broadcast message is received by everyone whether they
want it or not
 Tuples are extracted or copied under the control of the reader/
receiver
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17. DISCUSSION (2/2)
 Tuple Space Scalability
 Tuple Space won’t work on the Internet, because of
its underlying “distributed shared memory” idea
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