Difference between revisions of "Atomic Stack Assignment"

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=Motivation=
 +
We will build a thread-safe implementation of a Stack using atomics.
 
=Background=
 
=Background=
−
==Implicit Locks==
 
−
[https://docs.oracle.com/javase/tutorial/essential/concurrency/syncmeth.html synchronized methods]
 
−
 
 
==Atomics==
 
==Atomics==
 
[https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html AtomicReference<V>]
 
[https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html AtomicReference<V>]
 
: [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html#get-- get()]
 
: [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html#get-- get()]
 
: [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html#compareAndSet-V-V- compareAndSet(expect, update)]
 
: [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html#compareAndSet-V-V- compareAndSet(expect, update)]
−
 
−
=Node and Stack Interfaces=
 
−
==interface Node==
 
−
<nowiki>public interface Node<E> {
 
−
E value();
 
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Optional<Node<E>> nextNode();
 
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}</nowiki>
 
−
 
−
==interface Stack==
 
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<nowiki>public interface Stack<E> {
 
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void push(E value);
 
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Optional<E> peek();
 
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Optional<E> pop();
 
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}</nowiki>
 
−
 
−
==Example==
 
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===empty===
 
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<nowiki>Stack<String> stack = new NotThreadSafeStack<>(DefaultNode::new);</nowiki>
 
−
 
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[[File:Stack_empty.svg]]
 
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In this state, <code>stack.peek()</code> will return <code>Optional.empty()</code> and <code>stack.pop()</code> will also return <code>Optional.empty()</code>.
 
−
 
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===push A, B, C, D, E===
 
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<nowiki>Stack<String> stack = new NotThreadSafeStack<>(DefaultNode::new);
 
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stack.push("A");
 
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stack.push("B");
 
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stack.push("C");
 
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stack.push("D");
 
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stack.push("E");</nowiki>
 
−
 
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[[File:Stack_edcba.svg]]
 
−
 
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In this state, <code>stack.peek()</code> will return <code>Optional.of("E")</code>.
 
−
 
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===push A, B, C, D, E, pop===
 
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<nowiki>Stack<String> stack = new NotThreadSafeStack<>(DefaultNode::new);
 
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stack.push("A");
 
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stack.push("B");
 
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stack.push("C");
 
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stack.push("D");
 
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stack.push("E");
 
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Optional<String> optOfE = stack.pop();</nowiki>
 
−
 
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[[File:Stack_dcba.svg]]
 
−
 
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In this state, <code>optOfE</code> will hold <code>Optional.of("E")</code> and <code>stack.peek()</code> will return <code>Optional.of("D")</code>.
 
  
 
=Code To Implement=
 
=Code To Implement=
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==Node==
 
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<nowiki>public interface Node<E> {
 
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E value();
 
  
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Optional<Node<E>> nextNode();
+
==AtomicStack==
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}</nowiki>
+
While ConcurrentStack could simply rely on synchronized to provide thread-safety, AtomicStack must change its data structure.  To be {{ThreadSafeLink}}, AtomicStack must correctly use [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicReference.html AtomicReference<V>].  
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===DefaultNode===
 
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The mighty [https://en.wikipedia.org/wiki/Cons cons cell] goes back to the early days of computing.  People have been building amazing systems with this data structure since the 1950s.
 
  
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We will build an [https://www.javadoc.io/static/com.google.code.findbugs/jsr305/3.0.1/javax/annotation/concurrent/Immutable.html @Immutable] class DefaultNode which implements interface Node.
+
Do NOT hold any [https://docs.oracle.com/javase/tutorial/essential/concurrency/locksync.html intrinsic locks (via synchronized)] or hold any explicit [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Lock.html Locks]. It would be wasteful (and missing the point) to pay the lock overhead when the AtomicReference will get the job done.
−
 
 
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{{CodeToImplement|DefaultNode|value<br/>nextNode|stack.node.exercise|main}}
 
  
 +
{{CodeToImplement|AtomicStack|constructor<br/>push<br/>peek<br/>pop|stack.atomic.exercise}}
 
====constructor and instance variables====
 
====constructor and instance variables====
 +
Be sure to initialize whatever state you need to implement a mutable thread-safe Stack using atomics.
  
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The constructor
 
−
 
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<nowiki>public DefaultNode(E value, Optional<Node<E>> nextNode)</nowiki>
 
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is passed a value and a nextNode.  Hang on to this data in instance variables.  As instances of DefaultNode are to be immutable, the instance variables should be marked as <code>final</code>.
 
−
 
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====value====
 
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return the value.
 
−
 
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====nextNode====
 
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return the next node.
 
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==Stack==
 
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<nowiki>public interface Stack<E> {
 
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void push(E value);
 
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Optional<E> peek();
 
−
 
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Optional<E> pop();
 
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}</nowiki>
 
−
 
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===NotThreadSafeStack===
 
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[https://www.javadoc.io/static/com.google.code.findbugs/jsr305/3.0.1/javax/annotation/concurrent/NotThreadSafe.html @NotThreadSafe]
 
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{{CodeToImplement|NotThreadSafeStack|constructor<br/>nodeConstructor<br/>push<br/>peek<br/>pop|stack.notthreadsafe.exercise}}
 
−
 
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====constructor and instance variables====
 
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====nodeConstructor====
 
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====push====
 
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====peek====
 
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====pop====
 
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===ConcurrentStack===
 
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[https://www.javadoc.io/static/com.google.code.findbugs/jsr305/3.0.1/javax/annotation/concurrent/ThreadSafe.html @ThreadSafe]
 
−
 
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{{CodeToImplement|ConcurrentStack|constructor<br/>nodeConstructor<br/>push<br/>peek<br/>pop|stack.concurrent.exercise}}
 
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====constructor and instance variables====
 
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====nodeConstructor====
 
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====push====
 
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====peek====
 
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====pop====
 
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===AtomicStack===
 
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[https://www.javadoc.io/static/com.google.code.findbugs/jsr305/3.0.1/javax/annotation/concurrent/ThreadSafe.html @ThreadSafe]
 
−
 
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{{CodeToImplement|AtomicStack|constructor<br/>nodeConstructor<br/>push<br/>peek<br/>pop|stack.atomic.exercise}}
 
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====constructor and instance variables====
 
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====nodeConstructor====
 
 
====push====
 
====push====
 
====peek====
 
====peek====
Line 124: Line 23:
  
 
=Testing=
 
=Testing=
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{{TestSuite|StackTestSuite|stack.exercise}}
 
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==DefaultNode==
 
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{{TestSuite|_DefaultNodeTestSuite|stack.node.exercise}}
 
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==NotThreadSafeStack==
 
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{{TestSuite|_NotThreadSafeStackTestSuite|stack.notthreadsafe.exercise}}
 
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==ConcurrentStack==
 
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{{TestSuite|__ConcurrentStackTestSuite|stack.concurrent.exercise}}
 
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===sequential===
 
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{{TestSuite|_ConcurrentStackSequentialTestSuite|stack.concurrent.exercise}}
 
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===parallel===
 
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{{TestSuite|_ConcurrentStackParallelTestSuite|stack.concurrent.exercise}}
 
−
 
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==AtomicStack==
 
 
{{TestSuite|__AtomicStackTestSuite|stack.atomic.exercise}}
 
{{TestSuite|__AtomicStackTestSuite|stack.atomic.exercise}}
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===sequential===
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=Pledge, Acknowledgments, Citations=
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{{TestSuite|_AtomicStackSequentialTestSuite|stack.atomic.exercise}}
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{{Pledge|atomic-stack}}
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===parallel===
 
−
{{TestSuite|_AtomicStackParallelTestSuite|stack.atomic.exercise}}
 

Latest revision as of 02:25, 23 April 2024

Motivation

We will build a thread-safe implementation of a Stack using atomics.

Background

Atomics

AtomicReference<V>

get()
compareAndSet(expect, update)

Code To Implement

AtomicStack

While ConcurrentStack could simply rely on synchronized to provide thread-safety, AtomicStack must change its data structure. To be @ThreadSafe, AtomicStack must correctly use AtomicReference<V>.

Do NOT hold any intrinsic locks (via synchronized) or hold any explicit Locks. It would be wasteful (and missing the point) to pay the lock overhead when the AtomicReference will get the job done.

class: AtomicStack.java Java.png
methods: constructor
push
peek
pop
package: stack.atomic.exercise
source folder: student/src/main/java

constructor and instance variables

Be sure to initialize whatever state you need to implement a mutable thread-safe Stack using atomics.

push

peek

pop

Testing

class: __AtomicStackTestSuite.java Junit.png
package: stack.atomic.exercise
source folder: testing/src/test/java

Pledge, Acknowledgments, Citations

file: atomic-stack-pledge-acknowledgments-citations.txt

More info about the Honor Pledge

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