8/10/2019 Distributed Progrms

1/15

Distributed Programs

Dr. Mattox Beckman

Illinois Institute of Technology

Department of Computer Science

http://find/

8/10/2019 Distributed Progrms

2/15

Outline

http://find/

8/10/2019 Distributed Progrms

3/15

Motivation

Distributed programs are an amazing way of handling concurrency.

No interference!

Scales well to large systems.

http://find/

8/10/2019 Distributed Progrms

4/15

Syntax

A sequential process has the form

SS0; domj1gjSj od

where m 0andS0, . . . , Snare nondeterminstic programs. S0is the initialization code.

There may be loops inside of eachSi.

g B; Bis a guard is of formc?u an input command, or c!t an output command.

http://find/

8/10/2019 Distributed Progrms

5/15

Example

SR[SENDERRECIVER] (1)SENDERi:= 0; do i =|a|; link!a[i] i:= i+ 1 od (2)

RECEIVERj:= 0; do j =|b|; link?b[j] j:=j+ 1 od (3)

http://find/

8/10/2019 Distributed Progrms

6/15

Activity

Do the Distributed Program Activity

http://find/

8/10/2019 Distributed Progrms

7/15

Semantics

First we talk about termination.

< domj=1gjSj od , >

where forj {1, . . . , n}gjBj; jand |=mj=1Bj

We also want to talk about the meaning of a communication.

1=c?u2

=c!tEff(1, 2) =Eff(2, 1) =u:=t

http://find/http://goback/

8/10/2019 Distributed Progrms

8/15

Communication

Sk= dom1j=1gjRj od

Sl= dom2j=1hjTj od

gj1 =B1; 1hj2 =B2; 2

|=B1 B2

M[[Eff(1, 2)]]() ={}Si Sifori =k, lSkRj1 ; SkSl Tj2 ; Sl

http://find/http://goback/

8/10/2019 Distributed Progrms

9/15

Transforming to a nondeterministic program

Suppose each process has form

SiSi,0; domij=1Bi,j; i,jSi,j od

Letbe a list of matching communications:

={(i,j, k, l)|i,jand k,lmatch andi

8/10/2019 Distributed Progrms

10/15

Activity

Do the Distributed Conversion Activity

http://find/

8/10/2019 Distributed Progrms

11/15

Proving Deadlock

The partial correctness will be the same, but what about deadlock? Given

T(S) S1,0; S2,0; ; Sn,0;

do(i,j,k,l)Bi,j Bk,lEff(i,j, k,l); Si,j; Sk,lod

We defineTERMandBLOCK. How are they different?

TERMn

i=1mi

j=1 Bi,

jBLOCK

(i,j,k,l) (Bi,j Bk,l)

Which is the stronger ofTERMandBLOCK?

What doesBLOCK TERMtell us?

http://find/

8/10/2019 Distributed Progrms

12/15

Partial Correctness: Rule 19

{p}S1,0; ; Sn,0{I},

{I Bi,j Bk,l}Eff(i,j, k,l); Si,j; Sk,l{I}for all(i,j, k, l)

{p}S{I TERM}

What do we have to do to add weak total correctness?

http://find/

8/10/2019 Distributed Progrms

13/15

Weak Total Correctness: Rule 20

{p}S1,0; ; Sn,0{I},{I Bi,j Bk,l}Eff(i,j, k,l); Si,j; Sk,l{I}

for all(i,j, k, l) {I Bi,j Bk,l t=z}Eff(i,j, k,l); Si,j; Sk,l{t

8/10/2019 Distributed Progrms

14/15

Total Correctness: Rule 21

{p}S1,0; ; Sn,0{I},{I Bi,j Bk,l}Eff(i,j, k,l); Si,j; Sk,l{I}

for all(i,j, k, l) {I Bi,j Bk,l t=z}Eff(i,j, k,l); Si,j; Sk,l{t

8/10/2019 Distributed Progrms

15/15

Activity

Do the Distributed Deadlock Activity

http://find/