Difference between revisions of "Atomicity"

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=Code To Fix=
 
=Code To Fix=
: ''get then put is not atomic<br>
+
''get then put is not atomic<br>
 
call [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html#compute-K-java.util.function.BiFunction- compute]<br>call [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html#compute-K-java.util.function.BiFunction- compute]<br>use [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html ConcurrentHashMap]<br>use [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html ConcurrentHashMap]<br>or say shoot!<br>or say shoot!''
 
call [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html#compute-K-java.util.function.BiFunction- compute]<br>call [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html#compute-K-java.util.function.BiFunction- compute]<br>use [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html ConcurrentHashMap]<br>use [https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html ConcurrentHashMap]<br>or say shoot!<br>or say shoot!''
  

Revision as of 21:26, 12 April 2018

Motivation

Many race conditions can be prevented by proper encapsulation avoiding check-then-write and read-then-modify-then-write in non-atomically.

Background

Concurrency Tutorial

Synchronized Methods
Intrinsic Locks

ConcurrentMap

compute

Code To Investigate

YUCK

class: CheckThenActCourse.java DEMO: Java.png
methods: isSpaceRemaining
add
drop
package: atomicity.course.studio
source folder: src//java
public class CheckThenActCourse {
	private final Collection<Student> students;
	private final int limit;

	public CheckThenActCourse(int limit, Supplier<Collection<Student>> collectionSupplier) {
		this.students = collectionSupplier.get();
		this.limit = limit;
	}

	public int getLimit() {
		return this.limit;
	}

	public boolean isSpaceRemaining() {
		synchronized (this.students) {
			return this.students.size() < this.limit;
		}
	}

	public void add(Student student) {
		synchronized (this.students) {
			this.students.add(student);
		}
	}

	public boolean drop(Student student) {
		synchronized (this.students) {
			return this.students.remove(student);
		}
	}
}

Code To Implement

class: Course.java Java.png
methods: addIfSpace
drop
package: atomicity.course.studio
source folder: student/src/main/java

method: public boolean addIfSpace(Student student) Sequential.svg (sequential implementation only)

method: public boolean drop(Student student) Sequential.svg (sequential implementation only)

Code To Fix

get then put is not atomic
call compute
call compute
use ConcurrentHashMap
use ConcurrentHashMap
or say shoot!
or say shoot!

class: StockPortfolio.java Java.png
methods: transfer
package: atomicity.stockportfolio.studio
source folder: student/src/main/java
private final ConcurrentMap<String, Integer> map;
private int transfer(String listingSymbol, int deltaShareCount) {
	Integer oldValue = this.map.get(listingSymbol);
	Integer newValue;
	if (oldValue != null) {
		newValue = oldValue + deltaShareCount;
	} else {
		newValue = deltaShareCount;
	}
	this.map.put(listingSymbol, newValue);
	return newValue;
}

Testing Your Solution

Correctness

class: AtomicityTestSuite.java Junit.png
package: atomicity
source folder: testing/src/test/java