1. Structured Thread Models Kahn Process Networks, CSP, Go 1Dennis Kafura – CS5204 – Operating Systems

2. Structured Threads Dennis Kafura – CS5204 – Operating Systems Kahn Process Network Deterministic Processes Unbounded FIFO channels Non-blocking writes, blocking reads 2 Note: figure from Wikipedia

3. Structured Threads CS 5204 – Operating Systems3 Communicating Sequential Processes (CSP) single thread of control autonomous encapsulated named static synchronous reliable unidirectional point­to­point fixed topology sequential process communication channel

4. Structured Threads Go Language go routine  Executed concurrently  No return value  Syntax: go list.sort() Channels  Typed  Specified bounds on channel capacity  Used for Return value(s) from go routine Communication with/among go routine(s)  Syntax ci := make(chan int) // unbuffered channel of integers cj := make(chan int, 0) // unbuffered channel of integers Ck := make (chan int, 100) //buffered channel of integers Dennis Kafura – CS5204 – Operating Systems4 See: http://golang.org/doc/effective_go.html#concurrency

5. Structured Threads Go example Dennis Kafura – CS5204 – Operating Systems5 var sem = make(chan int, MaxOutstanding) func handle(r *Request) { sem <- 1 // Wait for active queue to drain. process(r) // May take a long time. <-sem // Done; enable next request to run. } func Serve(queue chan *Request) { for { req <-queue go handle(req) // Don't wait for handle to finish. }

6. Structured Threads Common Ideas Concurrency  Single threaded, deterministic processes  Non-determinism limited to interleaved execution of deterministic processes Interaction  Communication only via specified channels  no shared memory Unify communication and synchronization  Reads block when data unavailable  Write blocks if channel capacity exceeded or receiver not ready  Relates state of receiver to state of sender Dennis Kafura – CS5204 – Operating Systems6