From f979a4075d829af95eec40aaafcfc39e9eac243c Mon Sep 17 00:00:00 2001
From: Tomasz Lelek <tomekl007@gmail.com>
Date: Wed, 26 Apr 2017 12:57:16 +0200
Subject: [PATCH] BAEL-856 code for long adder and accumulator (#1723)

* BAEL-856 code for long adder and accumulator

* BAEL-856 rearange packages

* BAEL-856 Formatting
---
 .../accumulator/LongAccumulatorTest.java      | 41 ++++++++++++
 .../concurrent/adder/LongAdderTest.java       | 65 +++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 core-java/src/test/java/com/baeldung/concurrent/accumulator/LongAccumulatorTest.java
 create mode 100644 core-java/src/test/java/com/baeldung/concurrent/adder/LongAdderTest.java

diff --git a/core-java/src/test/java/com/baeldung/concurrent/accumulator/LongAccumulatorTest.java b/core-java/src/test/java/com/baeldung/concurrent/accumulator/LongAccumulatorTest.java
new file mode 100644
index 0000000000..46e107b607
--- /dev/null
+++ b/core-java/src/test/java/com/baeldung/concurrent/accumulator/LongAccumulatorTest.java
@@ -0,0 +1,41 @@
+package com.baeldung.concurrent.accumulator;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAccumulator;
+import java.util.function.LongBinaryOperator;
+import java.util.stream.IntStream;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class LongAccumulatorTest {
+
+    @Test
+    public void givenLongAccumulator_whenApplyActionOnItFromMultipleThrads_thenShouldProduceProperResult() throws InterruptedException {
+        //given
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+        LongBinaryOperator higherValueFinder = (currentValue, previousValue) -> currentValue > previousValue ? currentValue : previousValue;
+        LongAccumulator accumulator = new LongAccumulator(higherValueFinder, 0L);
+
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable accumulateAction = () -> IntStream
+          .rangeClosed(0, numberOfIncrements)
+          .forEach(accumulator::accumulate);
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(accumulateAction);
+        }
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+
+        assertEquals(accumulator.get(), 100);
+    }
+}
diff --git a/core-java/src/test/java/com/baeldung/concurrent/adder/LongAdderTest.java b/core-java/src/test/java/com/baeldung/concurrent/adder/LongAdderTest.java
new file mode 100644
index 0000000000..854db5d9b9
--- /dev/null
+++ b/core-java/src/test/java/com/baeldung/concurrent/adder/LongAdderTest.java
@@ -0,0 +1,65 @@
+package com.baeldung.concurrent.adder;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAdder;
+import java.util.stream.IntStream;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class LongAdderTest {
+    @Test
+    public void givenMultipleThread_whenTheyWriteToSharedLongAdder_thenShouldCalculateSumForThem() throws InterruptedException {
+        //given
+        LongAdder counter = new LongAdder();
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable incrementAction = () -> IntStream
+          .range(0, numberOfIncrements)
+          .forEach((i) -> counter.increment());
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(incrementAction);
+        }
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+
+        assertEquals(counter.sum(), numberOfIncrements * numberOfThreads);
+        assertEquals(counter.sum(), numberOfIncrements * numberOfThreads);
+    }
+
+    @Test
+    public void givenMultipleThread_whenTheyWriteToSharedLongAdder_thenShouldCalculateSumForThemAndResetAdderAfterward() throws InterruptedException {
+        //given
+        LongAdder counter = new LongAdder();
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable incrementAction = () -> IntStream
+          .range(0, numberOfIncrements)
+          .forEach((i) -> counter.increment());
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(incrementAction);
+        }
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+
+        assertEquals(counter.sumThenReset(), numberOfIncrements * numberOfThreads);
+        assertEquals(counter.sum(), 0);
+    }
+}