View Subcategory
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)
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")))
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*))
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)))))))
