Week 9

Assignment: Dining Java Philosophers

Assign 4
- PDF
- due: Tue, Mar 31, 11:59pm

Channels (cont'd)

CSP, Occam, and Golang!
Peter Welch's slides introducing CSP and occam-pi (but we will use Go this semester!)
- Occam-pi Lecture Notes
- Legoland: slides 83–end of basics.pdf
  - remember:
    - everything is a process in occam and CSP, and
    - processes must be composed (explicitly) in sequence (SEQ) or in parallel (PAR)

Go demo and starter code

copy from Marc's directory into your cs377 course directory:
```
$ cd ~/cs377
$ cd -r /home/mlsmith/cs377-examples/Go ./
```

you should see the following files in your local Go directory:

$ ls
csp-dining-phils.go       deadlock.go  sort-pump.go
csp-dining-phils-orig.go  sieve.go
$

Demo and codewalk of csp-dining-philosophers.go
- Based on an implementation found here
  - on the example given in section 5.3 of Hoare's 1978 CSP paper
  - and diagrammed more closely to the implementation in the CSP Book on p. 57
  - you can copy Marc's Go examples directory into your current directory with this command:
```
$ cp -r /home/mlsmith/cs377-examples/Go ./
```
- Go language features highlighted:
  - channels
  - select
- Design basis for solution in Go: go routines (processes)
  - room (communicates with philosophers over channels)
    - for philosophers to enter/leave – at most 4 at a time to prevent deadlocking, 5th philosopher blocks
  - forks (communicate with philosophers over channels)
  - philosophers (communicate with forks over channels)
- To run this program:
```
$ go run csp-dining-philosophers.go
```
- Nondeterminism
  - still!
  - sources?

Demo and codewalk: Sieve of Eratosthenes (Prime Number Sieve) sieve.go
- Go language features highlighted:
  - Only one looping construct in Go: for loop
    - all three parts are optional: init statement, conditional expression, post statement
  - channel declarations in function headers
    - can specify syntactically whether channel is for reading from:
      <-chan
      
      or writing to:
      
      chan<-
- To run this program:
```
$ go run sieve.go
```

Assignment 5 posted
- Sort Pump Gophers PDF
- see a similar example in occam on slides 13–31 of PHW's replicators lecture notes which can be found here
- Due: Thu, April 14th