Communicating Sequential Processes

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Eric Shull (@exupero) COMMUNICATING SEQUENTIAL PROCESSES

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SHARING MEMORY THE PROBLEM: NON-DETERMINISM RACE CONDITIONS DEADLOCKS HARD TO REPRODUCE HARD TO DEBUG HARD TO ENSURE RELIABILITY

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MUTEXES & LOCKS SEMAPHORES COMPARE & SWAP ATOMIC OPERATIONS SYNCHRONIZATION SOLUTIONS?

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WRITE LOCK? WRITE UNLOCK. READ LOCK? FAIL! READ LOCK? DEADLOCK? GOT IT! GOT IT! COMPLEX

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LEAKY

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NON-COMPOSABLE

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WANTED SIMPLICITY ABSTRACTIONS COMPOSABILITY CONCURRENCY

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PIPESSIMPLE COMPOSABLE NON-LEAKY PARALLEL

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CSP COMMUNICATING SEQUENTIAL PROCESSES BY C.A.R. HOARE

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(x → P) αCTR={up, right} µX : A • F(X) (s⌒t)n+1=s⌒(t⌒s)n⌒t A* = { s | s ↾ A = s } (c?x → P(x)) = (y : { y | channel(y) = c } → P(message(y))) (c!v → P) || (c?x → Q(x)) = c!v → (P || Q(v)) (right!v → P)≫(left?y → Q(y)) = P≫Q(v) DON’T PANIC π-calculus

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CONCEPTUAL THE MATH DEMONSTRATES SOUNDNESS

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PROCESSES NO THREADS NO SHARED MEMORY

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CHANNELS COMMUNICATION PASS DATA STRUCTURES VALUES AREN’T SHARED

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ONE-TO-ONE

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ONE-TO-MANY

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MANY-TO-ONE

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MANY-TO-MANY

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SOUNDS LIKE ERLANG, EXCEPT... SYNCHRONY ... CHANNEL, NOT MAILBOX

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CSPC.A.R. HOARE NEWSQUEAK ROB PIKE SQUEAKROB PIKE LUCA CARDELLI GO ROB PIKE KEN THOMPSON ROBERT GRIESEMER

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CHANNELS FUNCTIONS OR GOROUTINES FUNCTIONS OR GOROUTINES NOT THREADS MIGHT HAVE MILLIONS MORE LIGHTWEIGHT GOROUTINES: