Clojure concurrency

(do “Concurrency in Clojure”) (by (and “Alex” “Nithya”))

Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Introduction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Java Libraries JVM Evaluator Clojure/Repl Byte code public class StringUtils { public static boolean isBlank (String str) { int strLen; if (str == null || (strLen = str.length()) == 0) { return true; } for (int i = 0; i < strLen; i++) { if ((Character.isWhitespace(str.charAt(i)) == false)) { return false; } } return true; } } ( defn blank? [s] ( every? # ( Character/isWhitespace % ) s ) ) Fn name parameters body

[object Object],[object Object],[object Object],[object Object],Features ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Features Ins to generate the next component seq Item First Rest ( defn lazy-counter-iterate [base increment] ( iterate ( fn [n] ( + n increment ) ) base ) ) user=> ( def iterate-counter ( lazy-counter-iterate 2 3 ) ) user=> ( nth iterate-counter 1000000 ) user=> ( nth ( lazy-counter-iterate 2 3 ) 1000000 ) 3000002

[object Object],[object Object],[object Object],[object Object],State – You are doing it wrong Object Data Behaviour Object 2 Data Behaviour

Mutable Variables ,[object Object],location:Chennai location:Bangalore Values are constants, they never change (def location (ref “”) ) Identity - have different states in different point of time States value of an identity

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Concurrency

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],public class LinkedBlockingQueue <E> public E peek() { final ReentrantLock takeLock = this .takeLock; takeLock.lock(); try { Node<E> first = head . next ; if (first == null ) return null ; else return first. item ; } finally { takeLock.unlock(); } } Locks

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],C ompare A nd S wap

Enhancing Read Parallelism ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],public boolean add(E e) { final ReentrantLock lock = this . lock ; lock.lock(); try { Object[] elements = getArray(); int len = elements. length ; Object[] newElements = Arrays. copyOf (elements, len + 1); newElements[len] = e; setArray(newElements); return true ; } finally { lock.unlock(); } }

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],S oftware T ransaction M emory

Clojure Transactions Txn Txn Adam Mr B Minion R ~ 40 U ~ 30 (defstruct stock :name :quantity) (struct stock “CSK” 40) StocksList R ~ 30 Buy 10 Buy 5 Sell 10 CSK ~ 30 Txn Fail & Retry R - 40 U ~ 35 R - 30 U - 25 U ~ 40 Transaction Creation - (dosync (...))

Clojure STM ,[object Object],[object Object],[object Object],[object Object],[object Object]

STM ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Persistent Data Structures ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

PersistentHashMap ,[object Object],static interface INode { INode assoc (int shift, int hash, Object key, Object val, Box addedLeaf); LeafNode find (int hash, Object key); } BitMapIndexedNode

Concurrency Library ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Uncoordinated Coordinated Synchronous Var Atom Ref Asynchronous Agent

Vars ,[object Object],[object Object],[object Object],[object Object],[object Object],T1 T2 (def x 10) ; Global object (defn get-val [] (+ x y)) (defn fn [] (println x) (binding [x 2] (get-val)) Can’t see the binded value

Vars ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],user=> ( def variable 1 ) #'user/variable user=> ( . start ( Thread. ( fn [] ( println variable ) ) ) ) nil user=> 1 user=> (def variable 1) #'user/variable user=>(defn print [] (println variable)) user=> (.start (Thread. (fn [] (binding [variable 42] (print))))) nil user=> 1 (set! var-symbol value) (defn say-hello [] (println "Hello")) (binding [say-hello #(println "Goodbye")] (say-hello))

Vars... ,[object Object],[object Object],[object Object],[object Object],[object Object],( ns test-memoization ) ( defn triple[n] ( Thread/sleep 100 ) ( * n 3 ) ) ( defn invoke_triple [] ( map triple [ 1 2 3 4 4 3 2 1 ] ) ) ( time ( dorun ( invoke_triple ) ) ) -> "Elapsed time: 801.084578 msecs" ;(time (dorun (binding [triple (memoize triple)] (invoke_triple)))) -> "Elapsed time: 401.87119 msecs"

Atoms ,[object Object],[object Object],[object Object],[object Object],(def current-track (atom “Ooh la la la”)) (deref current-track ) or @current-track (reset! current-track “Humma Humma” (reset! current-track {:title : “Humma Humma”, composer” “What???”}) (def current-track (atom {:title : “Ooh la la la”, :composer: “ARR”})) (swap! current-track assoc {:title” : “Hosana”})

Refs ,[object Object],[object Object],[object Object],[object Object],[object Object]

Refs in Txn ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Changing Ref ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],( def account1 ( ref 1000 ) ) ( def account2 ( ref 2000 ) ) ( defn transfer "transfers amount of money from a to b" [a b amount] ( dosync ( alter a - amount ) ( alter b + amount ) ) ) ( transfer account1 account2 300 ) ( transfer account2 account1 50 ) ;@account1 -> 750 ;@account2 -> 2250

Validators ,[object Object],[object Object],[object Object],( ref initial-value :validator validator-fn ) user=> ( def my-ref ( ref 5 ) ) #'user/my-ref user=> ( set-validator! my-ref ( fn [x] ( < 0 x ) ) ) Nil user=> ( dosync ( alter my-ref – 10 ) ) #<CompilerException java.lang.IllegalStateException: Invalid Reference State> user=> ( dosync ( alter my-ref – 10 ) ( alter my-ref + 15 ) ) 10 user=> @my-ref 5

Watches ,[object Object],[object Object],[object Object],( add-watch identity key watch-function ) ( defn function-name [ key identity old-val new-val] expressions ) ( remove-watch identity key ) user=> ( defn my-watch [ key identity old-val new-val] ( println ( str "Old: " old-val ) ) ( println ( str "New: " new-val ) ) ) #'user/my-watch user=> ( def my-ref ( ref 5 ) ) #'user/my-ref user=> ( add-watch my-ref "watch1" my-watch ) #<Ref 5 > user=> ( dosync ( alter my-ref inc ) ) Old: 5

Other features... ,[object Object],[object Object],[object Object],[object Object],[object Object]

Agents ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Agents ,[object Object],[object Object],[object Object]

Agents ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Parallel Programming (defn heavy [f] (fn [& args] (Thread/sleep 1000) (apply f args))) (time (+ 5 5)) ;>>> "Elapsed time: 0.035009 msecs" (time ((heavy +) 5 5)) ;>>> "Elapsed time: 1000.691607 msecs" pmap (time (doall (map (heavy inc) [1 2 3 4 5]))) ;>>> "Elapsed time: 5001.055055 msecs" (time (doall (pmap (heavy inc) [1 2 3 4 5]))) ;>>> "Elapsed time: 1004.219896 msecs" ( pvalues (+ 5 5) (- 5 3) (* 2 4)) ( pcalls #(+ 5 2) #(* 2 5))

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Erlang Immutable Message Machine Machine Process Actors - a process that executes a function. Process - a lightweight user-space thread. Mailbox - essentially a queue with multiple producers

Actor Model ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Actor Model ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

References ,[object Object],[object Object],[object Object]

Clojure concurrency

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