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@eborden
Last active August 29, 2015 14:21
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Rust's "Dining Philosophers" solution reimplemented in unidiomatic Haskell
module Main where
import Prelude hiding (sequence)
import Control.Concurrent
import Data.Foldable
import Data.Traversable
data Philosopher = Philosopher
{ name :: String
, left :: Int
, right :: Int
}
data Table = Table { forks :: [MVar ()] }
type BufferLock = MVar ()
eat :: BufferLock -> Table -> Philosopher -> IO ()
eat buf t p = do
let l = forks t !! left p
r = forks t !! right p
withMVar l (\_ -> withMVar r (\ _ -> do
putStrLock buf (name p ++ " is eating")
threadDelay 1000000
putStrLock buf (name p ++ " is done eating")))
table :: Int -> IO Table
table i = fmap Table . sequence . take i . repeat $ newMVar ()
philosophers :: [Philosopher]
philosophers =
[ Philosopher "1" 0 1
, Philosopher "2" 1 2
, Philosopher "3" 2 3
, Philosopher "4" 3 4
, Philosopher "5" 0 4
]
-- Avoids interleaving of string output
putStrLock :: BufferLock -> String -> IO ()
putStrLock m s = withMVar m (\_ -> putStrLn s)
main = do
buf <- newMVar ()
t <- table (length philosophers)
forM_ philosophers (forkIO . eat buf t)
getLine
use std::thread;
use std::sync::{Mutex, Arc};
struct Philosopher {
name: String,
left: usize,
right: usize,
}
impl Philosopher {
fn new(name: &str, left: usize, right: usize) -> Self {
Philosopher {
name: name.to_string(),
left: left,
right: right,
}
}
fn eat(&self, table: &Table) {
let _left = table.forks[self.left].lock().unwrap();
let _right = table.forks[self.right].lock().unwrap();
println!("{} is eating", self.name);
thread::sleep_ms(1000);
println!("{} is done eating", self.name);
}
}
struct Table {
forks: Vec<Mutex<()>>,
}
fn main() {
let t = Arc::new(Table {forks:
vec![ Mutex::new(())
, Mutex::new(())
, Mutex::new(())
, Mutex::new(())
, Mutex::new(())
]
});
let p = vec![ Philosopher::new("1", 0, 1)
, Philosopher::new("2", 1 , 2)
, Philosopher::new("3", 2, 3)
, Philosopher::new("4", 3, 4)
, Philosopher::new("5", 0, 4)
];
let handles: Vec<_> = p.into_iter().map(|x| {
let t = t.clone();
thread::spawn(move || {
x.eat(&t);
})
}).collect();
for h in handles {
h.join().unwrap();
}
}
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