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Subdivide A Problem To A Pool Of Workers (No Shared Data)
Take a hard to compute problem and split it up between multiple worker threads. In your solution, try to fully utilize available cores or processors. (I'm looking at you, Python!)
Note: In this question, there should be no need for shared state between worker threads while the problem is being solved. Only after every thread completes computation are the answers recombined into a single output.
Example:
-Input-
(In python syntax)
In other words, a list of random strings.
-Output-
(In python syntax)
In other words, all possible permutations of each input string are computed.
Note: In this question, there should be no need for shared state between worker threads while the problem is being solved. Only after every thread completes computation are the answers recombined into a single output.
Example:
-Input-
(In python syntax)
["ab", "we", "tfe", "aoj"]
In other words, a list of random strings.
-Output-
(In python syntax)
[ ["ab", "ba", "aa", "bb", "a", "b"], ["we", "ew", "ww", "ee", "w", "e"], ...
In other words, all possible permutations of each input string are computed.
fsharp
open System
let input = [| "ab"; "we"; "tfe"; "aoj" |]
/// Computes all permutations of an array
let rec permute = function
| [| |] -> [| [| |] |]
| a ->
a
|> Array.mapi (fun i ai ->
// Take all elements in the array apart from the i.th, compute
// their permutations, then attach element i at the front of each perm
Array.sub a 0 i
|> Array.append (Array.sub a (i + 1) (a.Length - i - 1))
|> permute
|> Array.map (fun perm -> Array.append [| ai |] perm)
)
|> Array.concat
/// Computes all permutations of a string
let permuteString (s: string) =
s.ToCharArray()
|> permute
|> Array.map (fun p -> new String(p))
let output =
input
|> Array.map (fun word -> async { return (permuteString word) })
|> Async.Parallel
|> Async.RunSynchronously
let input = [| "ab"; "we"; "tfe"; "aoj" |]
/// Computes all permutations of an array
let rec permute = function
| [| |] -> [| [| |] |]
| a ->
a
|> Array.mapi (fun i ai ->
// Take all elements in the array apart from the i.th, compute
// their permutations, then attach element i at the front of each perm
Array.sub a 0 i
|> Array.append (Array.sub a (i + 1) (a.Length - i - 1))
|> permute
|> Array.map (fun perm -> Array.append [| ai |] perm)
)
|> Array.concat
/// Computes all permutations of a string
let permuteString (s: string) =
s.ToCharArray()
|> permute
|> Array.map (fun p -> new String(p))
let output =
input
|> Array.map (fun word -> async { return (permuteString word) })
|> Async.Parallel
|> Async.RunSynchronously
// like the Java and Groovy solutions, does not duplicate letters
open System
open System.Threading.Tasks
let input = [| "ab"; "we"; "tfe"; "aoj" |]
let factorial n =
seq { 1 .. n } |> Seq.reduce (*)
let swap (arr:'a[]) i j =
[| for k = 0 to arr.Length - 1 do
yield if k = i then arr.[j] elif k = j then arr.[i] else arr.[k] |]
let rec permutation (k:int,j:int) (r:'a[]) =
if j = (r.Length + 1) then r
else permutation (k/j+1, j+1) (swap r (j-1) (k%j))
let permutations (source:'a[]) = seq {
for k = 0 to (factorial source.Length) - 1 do
yield permutation (k,2) source
}
let permute (word:string) =
let letters = word.ToCharArray()
permutations letters
|> Seq.map (fun chars -> String(chars))
|> Array.ofSeq
let tasks =
input |> Array.map (fun word -> Task.Factory.StartNew(fun () -> permute word))
let taskResult (t:Task<_>) =
t.Result
let output = Task.Factory.ContinueWhenAll(tasks, fun ts -> Array.map taskResult ts).Result
open System
open System.Threading.Tasks
let input = [| "ab"; "we"; "tfe"; "aoj" |]
let factorial n =
seq { 1 .. n } |> Seq.reduce (*)
let swap (arr:'a[]) i j =
[| for k = 0 to arr.Length - 1 do
yield if k = i then arr.[j] elif k = j then arr.[i] else arr.[k] |]
let rec permutation (k:int,j:int) (r:'a[]) =
if j = (r.Length + 1) then r
else permutation (k/j+1, j+1) (swap r (j-1) (k%j))
let permutations (source:'a[]) = seq {
for k = 0 to (factorial source.Length) - 1 do
yield permutation (k,2) source
}
let permute (word:string) =
let letters = word.ToCharArray()
permutations letters
|> Seq.map (fun chars -> String(chars))
|> Array.ofSeq
let tasks =
input |> Array.map (fun word -> Task.Factory.StartNew(fun () -> permute word))
let taskResult (t:Task<_>) =
t.Result
let output = Task.Factory.ContinueWhenAll(tasks, fun ts -> Array.map taskResult ts).Result
clojure
(defn perm-chars [l]
"Returns a list of all possible permutations of strings with the
same size as the input string. This function will return duplicates
if the same character occurs multiple time in the string.
Ex: ab -> (aa ab ba ab)"
(if (string? l)
(recur (repeat (count l) l))
(let [s (first l)
r (rest l)]
(if (empty? r)
(map identity s)
(->> s
(map (fn [c] (map #(str c %) (perm-chars r))))
(flatten))))))
(defn perm-sz [s]
"Returns a list of all possible permutations of the input
string. May return duplicats.
Ex: ab -> (aa ab ba bb a b a b)"
(if-not (empty? s)
(let [r (perm-chars s)]
(if (= (count s) 1)
r
(->> r
(map #(perm-sz (apply str (rest %))))
(flatten)
(lazy-cat r))))))
(defn perm [s]
"Returns a list of all possible permutations of the input
string. The list of string is sorted and does not contain
duplicates.
Ex: ab -> (a aa ab b ba bb)"
(->> (reduce (fn [s e] (conj s e)) #{} (perm-sz s))
(map str)
(sort)))
(println (pmap perm ["ab" "we" "tfe" "aoj"]))
"Returns a list of all possible permutations of strings with the
same size as the input string. This function will return duplicates
if the same character occurs multiple time in the string.
Ex: ab -> (aa ab ba ab)"
(if (string? l)
(recur (repeat (count l) l))
(let [s (first l)
r (rest l)]
(if (empty? r)
(map identity s)
(->> s
(map (fn [c] (map #(str c %) (perm-chars r))))
(flatten))))))
(defn perm-sz [s]
"Returns a list of all possible permutations of the input
string. May return duplicats.
Ex: ab -> (aa ab ba bb a b a b)"
(if-not (empty? s)
(let [r (perm-chars s)]
(if (= (count s) 1)
r
(->> r
(map #(perm-sz (apply str (rest %))))
(flatten)
(lazy-cat r))))))
(defn perm [s]
"Returns a list of all possible permutations of the input
string. The list of string is sorted and does not contain
duplicates.
Ex: ab -> (a aa ab b ba bb)"
(->> (reduce (fn [s e] (conj s e)) #{} (perm-sz s))
(map str)
(sort)))
(println (pmap perm ["ab" "we" "tfe" "aoj"]))
(require 'cojure.contrib.combinatorics)
(pmap (fn [str]
(apply concat (map #(selections str (inc %))
(range (count str)))))
["ab", "we", "tfe", "aoj"])
(pmap (fn [str]
(apply concat (map #(selections str (inc %))
(range (count str)))))
["ab", "we", "tfe", "aoj"])
groovy
// as per Java answer, doesn't duplicate chars from input string, i.e. no 'aa'
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]
def threads = []
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
words.each { word ->
def t = Thread.start {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
threads << t
}
threads.each{ it.join() }
println ans
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]
def threads = []
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
words.each { word ->
def t = Thread.start {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
threads << t
}
threads.each{ it.join() }
println ans
// as per Java answer, doesn't duplicate chars from input string, i.e. no 'aa'
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
withParallelizer {
words.eachParallel { word ->
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
}
println ans
def ans = [].asSynchronized()
def words = ["ab", "we", "tfe", "aoj"]
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
withParallelizer {
words.eachParallel { word ->
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
ans << wordAns
}
}
println ans
Subdivide A Problem To A Pool Of Workers (Shared Data)
Take a hard to compute problem and split it up between multiple worker threads. In your solution, try to fully utilize available cores or processors. (I'm looking at you, Python!)
Note: In this question, there should be a need for shared state between worker threads while the problem is being solved.
Example:
-Conway Game of Life-
From Wikipedia:
The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, live or dead. Every cell interacts with its eight neighbors, which are the cells that are directly horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:
1. Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
2. Any live cell with more than three live neighbours dies, as if by overcrowding.
3. Any live cell with two or three live neighbours lives on to the next generation.
4. Any dead cell with exactly three live neighbours becomes a live cell.
The initial pattern constitutes the seed of the system. The first generation is created by applying the above rules simultaneously to every cell in the seed—births and deaths happen simultaneously, and the discrete moment at which this happens is sometimes called a tick (in other words, each generation is a pure function of the one before). The rules continue to be applied repeatedly to create further generations.
--However, for our purposes, we will assign a size to the game
Notice that in this problem, at each step or
Note: In this question, there should be a need for shared state between worker threads while the problem is being solved.
Example:
-Conway Game of Life-
From Wikipedia:
The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, live or dead. Every cell interacts with its eight neighbors, which are the cells that are directly horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:
1. Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
2. Any live cell with more than three live neighbours dies, as if by overcrowding.
3. Any live cell with two or three live neighbours lives on to the next generation.
4. Any dead cell with exactly three live neighbours becomes a live cell.
The initial pattern constitutes the seed of the system. The first generation is created by applying the above rules simultaneously to every cell in the seed—births and deaths happen simultaneously, and the discrete moment at which this happens is sometimes called a tick (in other words, each generation is a pure function of the one before). The rules continue to be applied repeatedly to create further generations.
--However, for our purposes, we will assign a size to the game
"board": 2^k * 2^k . That is, the board should be easy to subdivide.
Notice that in this problem, at each step or
"tick", each thread/process will need to share data with its neighborhood.
fsharp
/// Represents a single cell, along with the basic transition rule
type State =
| Alive
| Dead
member this.Transition numLiveNeighbors =
match this with
| Alive when numLiveNeighbors < 2 -> Dead
| Alive when numLiveNeighbors > 3 -> Dead
| Alive -> Alive
| Dead when numLiveNeighbors = 3 -> Alive
| _ -> Dead
member this.ToChar() =
match this with
| Alive -> '*'
| Dead -> ' '
static member OfChar = function
| ' ' -> Dead
| _ -> Alive
type Board (board: State[,]) =
member this.Item
with get(i,j) = board.[i,j]
and set (i,j) v = board.[i,j] <- v
member this.Length1 = Array2D.length1 board
member this.Length2 = Array2D.length2 board
member this.CountLiveNeighbors(i, j) =
[| (-1,-1); (-1,0); (-1,1); (0,-1); (0,1); (1,-1); (1,0); (1,1) |]
|> Array.sumBy (fun (di,dj) ->
if (i + di) > 0 && (i + di) < this.Length1 && (j+dj) > 0 && (j+dj) < this.Length2 then
match board.[i+di,j+dj] with
| Alive -> 1
| _ -> 0
else
0
)
member this.Clone() = Board(Array2D.copy board)
override this.ToString() =
[|
for i in 0 .. this.Length1 - 1 do
let l = [| for j in 0 .. this.Length2 - 1 do yield board.[i,j].ToChar() |]
yield new String(l)
|]
|> String.concat ("\n")
static member OfString (s: string) =
let states =
s.Split('\n')
|> Array.map (fun line -> line.ToCharArray() |> Array.map State.OfChar)
Board (Array2D.init states.Length states.[0].Length (fun i j -> states.[i].[j]))
static member Update (inboard: Board) =
let outboard = inboard.Clone()
let Worker (i1,i2,j1,j2) =
for i in i1 .. i2 do
for j in j1 .. j2 do
outboard.[i,j] <-
inboard.CountLiveNeighbors(i, j)
|> inboard.[i,j].Transition
let N1 = inboard.Length1 / 2
let N2 = inboard.Length2 / 2
[| (0,N1,0,N2); (N1+1,inboard.Length1-1,0,N2); (0,N1,N2+1,inboard.Length2-1); (N1+1,inboard.Length1-1,N2+1,inboard.Length2-1) |]
|> Array.map (fun bounds -> async { Worker bounds})
|> Async.Parallel
|> Async.RunSynchronously
|> ignore
outboard
let blinker = " \n * \n * \n * \n " |> Board.OfString
do
let after1cycles =
blinker
|> Board.Update
let after3cycles =
after1cycles
|> Board.Update
|> Board.Update
printfn "%s" (after3cycles.ToString())
type State =
| Alive
| Dead
member this.Transition numLiveNeighbors =
match this with
| Alive when numLiveNeighbors < 2 -> Dead
| Alive when numLiveNeighbors > 3 -> Dead
| Alive -> Alive
| Dead when numLiveNeighbors = 3 -> Alive
| _ -> Dead
member this.ToChar() =
match this with
| Alive -> '*'
| Dead -> ' '
static member OfChar = function
| ' ' -> Dead
| _ -> Alive
type Board (board: State[,]) =
member this.Item
with get(i,j) = board.[i,j]
and set (i,j) v = board.[i,j] <- v
member this.Length1 = Array2D.length1 board
member this.Length2 = Array2D.length2 board
member this.CountLiveNeighbors(i, j) =
[| (-1,-1); (-1,0); (-1,1); (0,-1); (0,1); (1,-1); (1,0); (1,1) |]
|> Array.sumBy (fun (di,dj) ->
if (i + di) > 0 && (i + di) < this.Length1 && (j+dj) > 0 && (j+dj) < this.Length2 then
match board.[i+di,j+dj] with
| Alive -> 1
| _ -> 0
else
0
)
member this.Clone() = Board(Array2D.copy board)
override this.ToString() =
[|
for i in 0 .. this.Length1 - 1 do
let l = [| for j in 0 .. this.Length2 - 1 do yield board.[i,j].ToChar() |]
yield new String(l)
|]
|> String.concat ("\n")
static member OfString (s: string) =
let states =
s.Split('\n')
|> Array.map (fun line -> line.ToCharArray() |> Array.map State.OfChar)
Board (Array2D.init states.Length states.[0].Length (fun i j -> states.[i].[j]))
static member Update (inboard: Board) =
let outboard = inboard.Clone()
let Worker (i1,i2,j1,j2) =
for i in i1 .. i2 do
for j in j1 .. j2 do
outboard.[i,j] <-
inboard.CountLiveNeighbors(i, j)
|> inboard.[i,j].Transition
let N1 = inboard.Length1 / 2
let N2 = inboard.Length2 / 2
[| (0,N1,0,N2); (N1+1,inboard.Length1-1,0,N2); (0,N1,N2+1,inboard.Length2-1); (N1+1,inboard.Length1-1,N2+1,inboard.Length2-1) |]
|> Array.map (fun bounds -> async { Worker bounds})
|> Async.Parallel
|> Async.RunSynchronously
|> ignore
outboard
let blinker = " \n * \n * \n * \n " |> Board.OfString
do
let after1cycles =
blinker
|> Board.Update
let after3cycles =
after1cycles
|> Board.Update
|> Board.Update
printfn "%s" (after3cycles.ToString())
clojure
; This is a "glider"
(def *start*
[".O......"
"..O....."
"OOO....."
"........"
"........"
"........"
"........"])
(def *width* (count (first *start*)))
(def *height* (count *start*))
(def *live* \O)
(def *dead* \.)
(def *n-generations-to-show* 3)
(defn cell-at
([b coord]
(cell-at b coord {:col 0 :row 0}))
([b coord offset]
(let [x (mod (+ (:col coord) (:col offset)) *width*)
y (mod (+ (:row coord) (:row offset)) *height*)]
(nth (nth b y) x))))
(defn neighbor-count [b coord]
(->> (for [x (range -1 2) y (range -1 2)] {:col x :row y})
(filter #(not (= {:col 0 :row 0} %)))
(map (partial cell-at b coord))
(reduce (fn [sum n] (+ sum (if (= *live* n) 1 0))) 0)))
(defn next-generation-cell [b coord]
(let [nc (neighbor-count b coord)]
(cond (< nc 2) *dead*
(> nc 3) *dead*
(= nc 3) *live*
true (cell-at b coord))))
(defn next-generation-row [b row]
(->> (range *width*)
(map #(next-generation-cell b {:col % :row row}))
(apply str)))
(defn next-generation [b]
(->> (range *height*)
(pmap #(next-generation-row b %))))
(defn generation-seq [b]
(let [ng (next-generation b)]
(lazy-seq (cons ng (generation-seq ng)))))
(doseq [g (take *n-generations-to-show* (generation-seq *start*))]
(doseq [l g]
(println l))
(println))
(shutdown-agents)
; This version calculates each separate line on a separate thread (pmap in next-generation)
(def *start*
[".O......"
"..O....."
"OOO....."
"........"
"........"
"........"
"........"])
(def *width* (count (first *start*)))
(def *height* (count *start*))
(def *live* \O)
(def *dead* \.)
(def *n-generations-to-show* 3)
(defn cell-at
([b coord]
(cell-at b coord {:col 0 :row 0}))
([b coord offset]
(let [x (mod (+ (:col coord) (:col offset)) *width*)
y (mod (+ (:row coord) (:row offset)) *height*)]
(nth (nth b y) x))))
(defn neighbor-count [b coord]
(->> (for [x (range -1 2) y (range -1 2)] {:col x :row y})
(filter #(not (= {:col 0 :row 0} %)))
(map (partial cell-at b coord))
(reduce (fn [sum n] (+ sum (if (= *live* n) 1 0))) 0)))
(defn next-generation-cell [b coord]
(let [nc (neighbor-count b coord)]
(cond (< nc 2) *dead*
(> nc 3) *dead*
(= nc 3) *live*
true (cell-at b coord))))
(defn next-generation-row [b row]
(->> (range *width*)
(map #(next-generation-cell b {:col % :row row}))
(apply str)))
(defn next-generation [b]
(->> (range *height*)
(pmap #(next-generation-row b %))))
(defn generation-seq [b]
(let [ng (next-generation b)]
(lazy-seq (cons ng (generation-seq ng)))))
(doseq [g (take *n-generations-to-show* (generation-seq *start*))]
(doseq [l g]
(println l))
(println))
(shutdown-agents)
; This version calculates each separate line on a separate thread (pmap in next-generation)
groovy
// some crude assumptions made for size and amount of parallelism
enum State { ALIVE, DEAD }
import static State.*
seed = '''\
* *
** **
** *
*
**
***
**
* \
'''
def computeNextGen(inboard, outboard, n) {
// crudely split into 4 chunks but could be smarter if we wanted
int half = n/2
def t1 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, 0, half) }
def t2 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, half, n) }
def t3 = Thread.start { computeNextGen(inboard, outboard, n, half, n, 0, half) }
def t4 = Thread.start { computeNextGen(inboard, outboard, n, half, n, half, n) }
[t1, t2, t3, t4].each{ it.join() }
}
def computeNextGen(inboard, outboard, n, minx, maxx, miny, maxy) {
for (int i = minx; i < maxx; i++)
for (int j = 0; j < maxy; j++)
if (i == 0 || i == n-1 || j == 0 || j == n-1)
outboard[i][j] = DEAD
for (int i = minx; i < maxx; i++) {
for (int j = miny; j < maxy; j++) {
if (i == 0 || i == n-1 || j == 0 || j == n-1)
continue
int count = 0
[[-1, 0, 1], [-1, 0, 1]].combinations().each{ dx, dy ->
if ((dx || dy) && inboard[i+dx][j+dy] == ALIVE) count++
}
switch(count) {
case {count == 3}:
case {inboard[i][j] == ALIVE && count == 2}:
outboard[i][j] = ALIVE; break
default:
outboard[i][j] = DEAD
}
}
}
}
void printBoard(board) {
println '--------'
println board*.collect{ it == DEAD ? ' ' : '*' }*.join().join('\n')
}
void initBoard(seed, board) {
def row = 0
seed.readLines().each { line ->
def col = 0
line.each { ch ->
board[row][col++] = ch == '*' ? ALIVE : DEAD
}
row++
}
}
def N = 8
def NUM_CYCLES = 3
def board1 = new State[N][N]
def board2 = new State[N][N]
initBoard(seed, board1)
NUM_CYCLES.times {
computeNextGen board1, board2, N
printBoard board2
computeNextGen board2, board1, N
printBoard board1
}
enum State { ALIVE, DEAD }
import static State.*
seed = '''\
* *
** **
** *
*
**
***
**
* \
'''
def computeNextGen(inboard, outboard, n) {
// crudely split into 4 chunks but could be smarter if we wanted
int half = n/2
def t1 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, 0, half) }
def t2 = Thread.start { computeNextGen(inboard, outboard, n, 0, half, half, n) }
def t3 = Thread.start { computeNextGen(inboard, outboard, n, half, n, 0, half) }
def t4 = Thread.start { computeNextGen(inboard, outboard, n, half, n, half, n) }
[t1, t2, t3, t4].each{ it.join() }
}
def computeNextGen(inboard, outboard, n, minx, maxx, miny, maxy) {
for (int i = minx; i < maxx; i++)
for (int j = 0; j < maxy; j++)
if (i == 0 || i == n-1 || j == 0 || j == n-1)
outboard[i][j] = DEAD
for (int i = minx; i < maxx; i++) {
for (int j = miny; j < maxy; j++) {
if (i == 0 || i == n-1 || j == 0 || j == n-1)
continue
int count = 0
[[-1, 0, 1], [-1, 0, 1]].combinations().each{ dx, dy ->
if ((dx || dy) && inboard[i+dx][j+dy] == ALIVE) count++
}
switch(count) {
case {count == 3}:
case {inboard[i][j] == ALIVE && count == 2}:
outboard[i][j] = ALIVE; break
default:
outboard[i][j] = DEAD
}
}
}
}
void printBoard(board) {
println '--------'
println board*.collect{ it == DEAD ? ' ' : '*' }*.join().join('\n')
}
void initBoard(seed, board) {
def row = 0
seed.readLines().each { line ->
def col = 0
line.each { ch ->
board[row][col++] = ch == '*' ? ALIVE : DEAD
}
row++
}
}
def N = 8
def NUM_CYCLES = 3
def board1 = new State[N][N]
def board2 = new State[N][N]
initBoard(seed, board1)
NUM_CYCLES.times {
computeNextGen board1, board2, N
printBoard board2
computeNextGen board2, board1, N
printBoard board1
}
Create a multithreaded "Hello World"
Create a program which outputs the string
Example:
-Output-
Thread one says Hello World!
Thread two says Hello World!
Thread four says Hello World!
Thread three says Hello World!
-Notice that the threads can print in any order.
"Hello World" to the console, multiple times, using separate threads or processes.
Example:
-Output-
Thread one says Hello World!
Thread two says Hello World!
Thread four says Hello World!
Thread three says Hello World!
-Notice that the threads can print in any order.
fsharp
let mappedString =
["Thread one says Hello World!";
"Thread two says Hello World!";
"Thread four says Hello World!";
"Thread three says Hello World!"]
|> Seq.map (fun str -> async { printfn "%s" str })
Async.RunSynchronously (Async.Parallel mappedString)
["Thread one says Hello World!";
"Thread two says Hello World!";
"Thread four says Hello World!";
"Thread three says Hello World!"]
|> Seq.map (fun str -> async { printfn "%s" str })
Async.RunSynchronously (Async.Parallel mappedString)
erlang
-module(spam).
-export([spam/1]).
spam(N) when N<5 ->
spawn(fun() -> io:format("Hello World from thread ~p~n",[N]) end),
spam(N+1);
spam(_) -> void.
-export([spam/1]).
spam(N) when N<5 ->
spawn(fun() -> io:format("Hello World from thread ~p~n",[N]) end),
spam(N+1);
spam(_) -> void.
clojure
(doseq [msg ["one" "two" "three" "four"]]
(future (println "Thread" msg "says Hello World!")))
(future (println "Thread" msg "says Hello World!")))
(dorun (pmap #(println (str "Thread " % " says Hello World!")) '("one" "two" "three" "four")))
(dorun (map (fn [n] (.start (Thread. #(println (str "Thread " n " says Hello World!")))))
'("one" "two" "three" "four")))
'("one" "two" "three" "four")))
groovy
["one","two","three","four"].each { tid ->
Thread.start {
println "Thread $tid says Hello World!"
}
}
Thread.start {
println "Thread $tid says Hello World!"
}
}
import static groovyx.gpars.Parallelizer.*
withParallelizer {
["one","two","three","four"].eachParallel {
println "Thread $it says Hello World!"
}
}
withParallelizer {
["one","two","three","four"].eachParallel {
println "Thread $it says Hello World!"
}
}
Create read/write lock on a shared resource.
Create multiple threads or processes who are either readers or writers. There should be more readers then writers.
(From Wikipedia):
Multiple readers can read the data in parallel but an exclusive lock is needed while writing the data. When a writer is writing the data, readers will be blocked until the writer is finished writing.
Example:
-Output-
Thread one says that the value is 8.
Thread three says that the value is 8.
Thread two is taking the lock.
Thread four tried to read the value, but could not.
Thread five tried to write to the value, but could not.
Thread two is changing the value to 9.
Thread two is releasing the lock.
Thread four says that the value is 9.
...
--Notice that when a needed resource is locked, a thread can set a timer and try again in the future, or wait to be notified that the resource is no longer locked.
(From Wikipedia):
Multiple readers can read the data in parallel but an exclusive lock is needed while writing the data. When a writer is writing the data, readers will be blocked until the writer is finished writing.
Example:
-Output-
Thread one says that the value is 8.
Thread three says that the value is 8.
Thread two is taking the lock.
Thread four tried to read the value, but could not.
Thread five tried to write to the value, but could not.
Thread two is changing the value to 9.
Thread two is releasing the lock.
Thread four says that the value is 9.
...
--Notice that when a needed resource is locked, a thread can set a timer and try again in the future, or wait to be notified that the resource is no longer locked.
fsharp
open System.Threading
let lock = new ReaderWriterLock()
let mutable value = 0
let lockTimeout = 1
let ReaderThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireReaderLock(lockTimeout)
try
printfn "Thread %i says that the value is %i" t value
finally
lock.ReleaseReaderLock()
with _ ->
printfn "Thread %i tried to read the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))
let WriterThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireWriterLock(lockTimeout)
try
value <- random.Next(10)
printfn "Thread %i is changing the value to %i" t value
Thread.MemoryBarrier()
finally
lock.ReleaseWriterLock()
printfn "Thread %i is releasing the lock." t
with _ ->
printfn "Thread %i tried to write the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))
[| 0 .. 20 |]
|> Array.iter (fun t ->
async {
if t % 3 = 0 then
WriterThread t
else
ReaderThread t
}
|> Async.Start
)
let lock = new ReaderWriterLock()
let mutable value = 0
let lockTimeout = 1
let ReaderThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireReaderLock(lockTimeout)
try
printfn "Thread %i says that the value is %i" t value
finally
lock.ReleaseReaderLock()
with _ ->
printfn "Thread %i tried to read the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))
let WriterThread t =
let random = new System.Random()
for i in 0 .. 100 do
try
lock.AcquireWriterLock(lockTimeout)
try
value <- random.Next(10)
printfn "Thread %i is changing the value to %i" t value
Thread.MemoryBarrier()
finally
lock.ReleaseWriterLock()
printfn "Thread %i is releasing the lock." t
with _ ->
printfn "Thread %i tried to write the value, but could not (timeout)." t
Thread.Sleep(random.Next(50))
[| 0 .. 20 |]
|> Array.iter (fun t ->
async {
if t % 3 = 0 then
WriterThread t
else
ReaderThread t
}
|> Async.Start
)
clojure
; NOTE! Using explicit locking is NOT the Clojure way. It was done
; this way in order to comply exactly with the problem
; specification. Sharing data in Clojure would normally be done by
; using "atom", "agent" or "ref" depending on situation. None of those
; methods would ever result in the reader not being able to read (as
; required by the problem) since reading is wait-free in clojure.
(def *readers* (map #(agent %) '("one" "two" "three")))
(def *writers* (map #(agent %) '("four" "five")))
(def *mutex* (agent :unlocked))
(def *value* 0)
; mutex implementation
(defn lock [state who success-fn fail-fn]
(send who (if (= state :locked) fail-fn success-fn))
:locked)
(defn unlock [mutex]
:unlocked)
; Must be invoked with send-off since this handler blocks
(defn rand-sleep [state next-fn]
(Thread/sleep (rand-int 5))
(send *agent* next-fn)
state)
; Reader functions
(declare try-read)
(defn reader-got-lock [name]
(println (format "Thread %s says that the value is %d." name *value*))
(send *mutex* unlock)
(send-off *agent* rand-sleep try-read)
name)
(defn reader-did-not-get-lock [name]
(println (format "Thread %s tried to read the value, but could not." name))
(send-off *agent* rand-sleep try-read)
name)
(defn try-read [name]
(send *mutex* lock *agent* reader-got-lock reader-did-not-get-lock)
name)
; Writer functions
(declare try-write)
(defn writer-got-lock [name]
(println (format "Thread %s is taking the lock." name))
(def *value* (rand-int 10))
(println (format "Thread %s is changing the value to %d." name *value*))
(send *mutex* unlock)
(println (format "Thread %s is relasing the lock." name))
(send-off *agent* rand-sleep try-write)
name)
(defn writer-did-not-get-lock [name]
(println (format "Thread %s tried to write the value, but could not." name))
(send-off *agent* rand-sleep try-write)
name)
(defn try-write [name]
(send *mutex* lock *agent* writer-got-lock writer-did-not-get-lock)
name)
(dorun (map #(send % try-write) *writers*))
(dorun (map #(send % try-read) *readers*))
; this way in order to comply exactly with the problem
; specification. Sharing data in Clojure would normally be done by
; using "atom", "agent" or "ref" depending on situation. None of those
; methods would ever result in the reader not being able to read (as
; required by the problem) since reading is wait-free in clojure.
(def *readers* (map #(agent %) '("one" "two" "three")))
(def *writers* (map #(agent %) '("four" "five")))
(def *mutex* (agent :unlocked))
(def *value* 0)
; mutex implementation
(defn lock [state who success-fn fail-fn]
(send who (if (= state :locked) fail-fn success-fn))
:locked)
(defn unlock [mutex]
:unlocked)
; Must be invoked with send-off since this handler blocks
(defn rand-sleep [state next-fn]
(Thread/sleep (rand-int 5))
(send *agent* next-fn)
state)
; Reader functions
(declare try-read)
(defn reader-got-lock [name]
(println (format "Thread %s says that the value is %d." name *value*))
(send *mutex* unlock)
(send-off *agent* rand-sleep try-read)
name)
(defn reader-did-not-get-lock [name]
(println (format "Thread %s tried to read the value, but could not." name))
(send-off *agent* rand-sleep try-read)
name)
(defn try-read [name]
(send *mutex* lock *agent* reader-got-lock reader-did-not-get-lock)
name)
; Writer functions
(declare try-write)
(defn writer-got-lock [name]
(println (format "Thread %s is taking the lock." name))
(def *value* (rand-int 10))
(println (format "Thread %s is changing the value to %d." name *value*))
(send *mutex* unlock)
(println (format "Thread %s is relasing the lock." name))
(send-off *agent* rand-sleep try-write)
name)
(defn writer-did-not-get-lock [name]
(println (format "Thread %s tried to write the value, but could not." name))
(send-off *agent* rand-sleep try-write)
name)
(defn try-write [name]
(send *mutex* lock *agent* writer-got-lock writer-did-not-get-lock)
name)
(dorun (map #(send % try-write) *writers*))
(dorun (map #(send % try-read) *readers*))
groovy
def lock = new ReentrantLock()
Integer value = 8
20.times { i ->
if (i % 3 == 0) {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to write the value, but could not."
lock.lock()
}
value = (int) (Math.random() * 10)
println "Thread " + i + " is changing the value to " + value
lock.unlock()
println "Thread " + i + " is releasing the lock."
}
} else {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to read the value, but could not."
lock.lock()
}
println "Thread " + i + " says that the value is " + value + "."
lock.unlock()
}
}
}
Integer value = 8
20.times { i ->
if (i % 3 == 0) {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to write the value, but could not."
lock.lock()
}
value = (int) (Math.random() * 10)
println "Thread " + i + " is changing the value to " + value
lock.unlock()
println "Thread " + i + " is releasing the lock."
}
} else {
Thread.start {
if (!lock.tryLock()) {
println "Thread " + i + " tried to read the value, but could not."
lock.lock()
}
println "Thread " + i + " says that the value is " + value + "."
lock.unlock()
}
}
}
Separate user interaction and computation.
Allow your program to accept user interaction while conducting a long running computation.
Example:
Hello user! Please input a string to permute: (input thread)
abcdef
Passing on abcdef... (input thread)
Please input another string to permute: (input thread)
lol
Passing on lol... (input thread)
Done Work On abcdef! (worker thread)
Please input another string to permute: (input thread)
EXIT
Quitting, I
--Notice, that this could be accomplished on the command line or within a GUI. The point is that computation and user interaction should take place on separate threads of control.
Example:
Hello user! Please input a string to permute: (input thread)
abcdef
Passing on abcdef... (input thread)
Please input another string to permute: (input thread)
lol
Passing on lol... (input thread)
Done Work On abcdef! (worker thread)
["abcdef", "abcefd", ... ] (worker thread)
Please input another string to permute: (input thread)
EXIT
Quitting, I
'll let my worker thread know... (input thread)
We're quitting! Alright! (worker thread)
--Notice, that this could be accomplished on the command line or within a GUI. The point is that computation and user interaction should take place on separate threads of control.
fsharp
open System
/// Computes all permutations of an array
let rec permute = function
| [| |] -> [| [| |] |]
| a ->
a
|> Array.mapi (fun i ai ->
Array.sub a 0 i
|> Array.append (Array.sub a (i + 1) (a.Length - i - 1))
|> permute
|> Array.map (fun perm -> Array.append [| ai |] perm)
)
|> Array.concat
/// Computes all permutations of a string
let permuteString (s: string) =
s.ToCharArray()
|> permute
|> Array.map (fun p -> new String(p))
type PermuteMessage =
| PermuteString of string
| Cancel
let mailbox = new MailboxProcessor<PermuteMessage>(fun inbox ->
let rec loop() =
async {
let! msg = inbox.Receive()
match msg with
| PermuteString s ->
printfn "[Worker] Starting to work on %s" s
let p = permuteString s
printfn "[Worker] Done my work on %s" s
let firstElems =
if s.Length > 4 then
let first = p |> Seq.truncate 4 |> Seq.toArray
String.Join(", ", first) + ", ..."
else
String.Join(", ", p)
printfn "[Worker] Result is %s" firstElems
return! loop()
| Cancel ->
printfn "[Worker] Nuff done, I'm quitting!"
return ()
}
loop()
)
do
printfn "[Input] Setting up worker."
mailbox.Start()
let loop = ref true
while !loop do
printfn "[Input] Please enter a word, or EXIT to exit"
let s = Console.ReadLine()
match s with
| "EXIT" ->
printfn "[Input] Sending worker the cancellation notice."
mailbox.Post(Cancel)
loop := false
| _ ->
printfn "[Input] Sending task to the worker."
mailbox.Post(PermuteString s)
/// Computes all permutations of an array
let rec permute = function
| [| |] -> [| [| |] |]
| a ->
a
|> Array.mapi (fun i ai ->
Array.sub a 0 i
|> Array.append (Array.sub a (i + 1) (a.Length - i - 1))
|> permute
|> Array.map (fun perm -> Array.append [| ai |] perm)
)
|> Array.concat
/// Computes all permutations of a string
let permuteString (s: string) =
s.ToCharArray()
|> permute
|> Array.map (fun p -> new String(p))
type PermuteMessage =
| PermuteString of string
| Cancel
let mailbox = new MailboxProcessor<PermuteMessage>(fun inbox ->
let rec loop() =
async {
let! msg = inbox.Receive()
match msg with
| PermuteString s ->
printfn "[Worker] Starting to work on %s" s
let p = permuteString s
printfn "[Worker] Done my work on %s" s
let firstElems =
if s.Length > 4 then
let first = p |> Seq.truncate 4 |> Seq.toArray
String.Join(", ", first) + ", ..."
else
String.Join(", ", p)
printfn "[Worker] Result is %s" firstElems
return! loop()
| Cancel ->
printfn "[Worker] Nuff done, I'm quitting!"
return ()
}
loop()
)
do
printfn "[Input] Setting up worker."
mailbox.Start()
let loop = ref true
while !loop do
printfn "[Input] Please enter a word, or EXIT to exit"
let s = Console.ReadLine()
match s with
| "EXIT" ->
printfn "[Input] Sending worker the cancellation notice."
mailbox.Post(Cancel)
loop := false
| _ ->
printfn "[Input] Sending task to the worker."
mailbox.Post(PermuteString s)
clojure
(defn background-computation [_ s]
(let [res (permutations s)]
(println (format "Done Work On %s!" s))
(println res)))
(defn shutdown-app [_]
(println "We're quitting! Alright!")
(shutdown-agents))
(println "Hello user! Please input a string to permute: ")
(let [worker-agent (agent nil)]
(loop [input (str (read))]
(if (= input "EXIT")
(do (println "Quitting, I'll let my worker thread know...")
(send worker-agent shutdown-app))
(do (println (format "Passing on %s..." input))
(send worker-agent background-computation input)
(println "Please input another string to permute: ")
(recur (str (read)))))))
(let [res (permutations s)]
(println (format "Done Work On %s!" s))
(println res)))
(defn shutdown-app [_]
(println "We're quitting! Alright!")
(shutdown-agents))
(println "Hello user! Please input a string to permute: ")
(let [worker-agent (agent nil)]
(loop [input (str (read))]
(if (= input "EXIT")
(do (println "Quitting, I'll let my worker thread know...")
(send worker-agent shutdown-app))
(do (println (format "Passing on %s..." input))
(send worker-agent background-computation input)
(println "Please input another string to permute: ")
(recur (str (read)))))))
groovy
def threads = new ConcurrentLinkedQueue<Thread>()
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
println 'Welcome to the parallel permuter'
System.in.withReader { r ->
while (true) {
print 'Enter word:'
def word = r.readLine()
if (word == 'EXIT') {
while (!threads.isEmpty())
threads.poll().stop(new ThreadDeath())
break
} else
threads << Thread.start {
try {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
println '\nAnswer:' + wordAns
print 'Enter word:'
} catch (ThreadDeath td) {
println 'Thread aborted!'
}
}
}
}
void permutations(String prefix, String w, Set<String> permSet) {
int n = w.size()
if (!n) permSet << prefix
else n.times { i ->
permutations(prefix + w[i], w[0..<i] + w[i+1..<n], permSet)
}
}
println 'Welcome to the parallel permuter'
System.in.withReader { r ->
while (true) {
print 'Enter word:'
def word = r.readLine()
if (word == 'EXIT') {
while (!threads.isEmpty())
threads.poll().stop(new ThreadDeath())
break
} else
threads << Thread.start {
try {
def wordAns = [] as Set
for (int i = 0; i < word.size(); i++)
for (int j = i + 1; j <= word.size(); j++)
permutations("", word[i..<j], wordAns)
println '\nAnswer:' + wordAns
print 'Enter word:'
} catch (ThreadDeath td) {
println 'Thread aborted!'
}
}
}
}
