What I Teach(Do what I say, not what I do)

Andrew LumsdaineIndiana University

B524: Parallelism in Programming Languages and Systems

Andrew LumsdaineComputer Science Department

Indiana UniversityBloomington, IN 47401

Course Text

• Andrews, “Foundations of Multithreaded, Parallel, and Distributed Programming”

Supplemental Text

• Schneider, “On Concurrent Programming”

Supplemental Texts

• Andrews, Concurrent Programming

Course Outline

• Introduction / overview• Program logic• Semantics of concurrency• Safety properties• Fine grained atomicity• Semaphores, locks, etc• Message passing• Case studies

Semantics of Concurrent Execution

• Await Rule

• Co Rule

{P Λ B} S {Q}

{P} < await (B) S;> {Q}

{Pi} Si {Qi} are interference free

{P1 Λ P2 Λ … Pn}Co S1 ; // S2 … // Sn; oc{Q1 Λ Q2 Λ … Qn}

Critical Section Problemsem mutex = 1;

process CS[i = 1 to n] { while (true) { P(mutex); critical section; V(mutex); noncritical section; }}

Correctness?

sem mx = 1;

process CS[i = 1 to n] { while (true) { P(mx); critical section; V(mx); noncritical section; }}

€

I :mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

Is {I} preserved by P(mx)?

Correctness

€

{V = ( : in(CS j )j≠ i∑ ∨after(CS j ) :1)}

entry i

{V = ( : in(CS j )j≠ i∑ ∨after(CS j ) :1)}

€

{¬(in(CSi)∨after(CSi))}

entry i{in(CSi)}

Correctness

€

{V = ( : in(CS j )j∑ ∨after(CS j ) :1)}

entry i

{V +1= ( : in(CS j )j∑ ∨after(CS j ) :1)}

Correctness

€

{mx > 0⇒ (mx −1=1− (V +1)}

entry i{mx =1= (V +1)}

€

(mx −1=1− (V +1))⇒ (mx > 0⇒ (mx −1=1− (V +1)))

€

{mx −1=1− (V +1)}

entry i{mx =1− (V +1)}

Correctness

€

mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

∧V = ( : in(CS j )j∑ ∨after(CS j ) :1)

⇒ mx −1=1− (V +1)∧V = ( : in(CS j )j∑ ∨after(CS j ) :1)

€

mx =1− (V +1)∧V +1= ( : in(CS j )j∑ ∨after(CS j ) :1)

⇒ mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

Correctness

€

mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

∧V = ( : in(CS j )j∑ ∨after(CS j ) :1)

entry i

mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

€

mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)

entry i

mx =1− ( : in(CS j )j∑ ∨after(CS j ) :1)