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issue 1628 handled, removed mutex and semaphore from catalog. (#1634)

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* issue 1628 handled, removed mutex and semaphore from catalog.

* issue1634, modules still exiting in pom.xml

Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>
This commit is contained in:
Rohit Singh 2021-01-27 01:49:36 +05:30 committed by GitHub
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31
mutex/README.md
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---
layout: pattern
title: Mutex
folder: mutex
permalink: /patterns/mutex/
categories: Concurrency
tags:
- Decoupling
---
## Also known as
* Mutual Exclusion Lock
* Binary Semaphore
## Intent
Create a lock which only allows a single thread to access a resource at any one instant.
## Class diagram
![alt text](./etc/mutex.png "Mutex")
## Applicability
Use a Mutex when
* You need to prevent two threads accessing a critical section at the same time
* Concurrent access to a resource could lead to a race condition
## Credits
* [Lock (computer science)](http://en.wikipedia.org/wiki/Lock_(computer_science))
* [Semaphores](http://tutorials.jenkov.com/java-concurrency/semaphores.html)

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mutex/etc/mutex.urm.puml
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@startuml
package com.iluwatar.mutex {
class App {
+ App()
+ main(args : String[]) {static}
}
class Jar {
- beans : int
- lock : Lock
+ Jar(beans : int, lock : Lock)
+ takeBean() : boolean
}
interface Lock {
+ acquire() {abstract}
+ release() {abstract}
}
class Mutex {
- owner : Object
+ Mutex()
+ acquire()
+ getOwner() : Object
+ release()
}
}
Jar --> "-lock" Lock
Mutex ..|> Lock
@enduml

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mutex/pom.xml
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<?xml version="1.0"?>
<!--
The MIT License
Copyright © 2014-2019 Ilkka Seppälä
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
-->
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId>
<version>1.24.0-SNAPSHOT</version>
</parent>
<artifactId>mutex</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<configuration>
<archive>
<manifest>
<mainClass>com.iluwatar.mutex.App</mainClass>
</manifest>
</archive>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

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mutex/src/main/java/com/iluwatar/mutex/App.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
/**
* A Mutex prevents multiple threads from accessing a resource simultaneously.
*
* <p>In this example we have two thieves who are taking beans from a jar. Only one thief can take
* a bean at a time. This is ensured by a Mutex lock which must be acquired in order to access the
* jar. Each thief attempts to acquire the lock, take a bean and then release the lock. If the lock
* has already been acquired, the thief will be prevented from continuing (blocked) until the lock
* has been released. The thieves stop taking beans once there are no beans left to take.
*/
public class App {
/**
* main method.
*/
public static void main(String[] args) {
var mutex = new Mutex();
var jar = new Jar(1000, mutex);
var peter = new Thief("Peter", jar);
var john = new Thief("John", jar);
peter.start();
john.start();
}
}

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mutex/src/main/java/com/iluwatar/mutex/Jar.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
/**
* A Jar has a resource of beans which can only be accessed by a single Thief (thread) at any one
* time. A Mutex lock is used to prevent more than one Thief taking a bean simultaneously.
*/
public class Jar {
/**
* The lock which must be acquired to access the beans resource.
*/
private final Lock lock;
/**
* The resource within the jar.
*/
private int beans;
public Jar(int beans, Lock lock) {
this.beans = beans;
this.lock = lock;
}
/**
* Method for a thief to take a bean.
*/
public boolean takeBean() {
var success = false;
try {
lock.acquire();
success = beans > 0;
if (success) {
beans = beans - 1;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.release();
}
return success;
}
}

35
mutex/src/main/java/com/iluwatar/mutex/Lock.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
/**
* Lock is an interface for a lock which can be acquired and released.
*/
public interface Lock {
void acquire() throws InterruptedException;
void release();
}

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mutex/src/main/java/com/iluwatar/mutex/Mutex.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
/**
* Mutex is an implementation of a mutual exclusion lock.
*/
public class Mutex implements Lock {
/**
* The current owner of the lock.
*/
private Object owner;
/**
* Returns the current owner of the Mutex, or null if available.
*/
public Object getOwner() {
return owner;
}
/**
* Method called by a thread to acquire the lock. If the lock has already been acquired this will
* wait until the lock has been released to re-attempt the acquire.
*/
@Override
public synchronized void acquire() throws InterruptedException {
while (owner != null) {
wait();
}
owner = Thread.currentThread();
}
/**
* Method called by a thread to release the lock.
*/
@Override
public synchronized void release() {
if (Thread.currentThread() == owner) {
owner = null;
notify();
}
}
}

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mutex/src/main/java/com/iluwatar/mutex/Thief.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Thief is a class which continually tries to acquire a jar and take a bean from it. When the jar
* is empty the thief stops.
*/
public class Thief extends Thread {
private static final Logger LOGGER = LoggerFactory.getLogger(Thief.class);
/**
* The name of the thief.
*/
private final String name;
/**
* The jar.
*/
private final Jar jar;
public Thief(String name, Jar jar) {
this.name = name;
this.jar = jar;
}
/**
* In the run method the thief repeatedly tries to take a bean until none are left.
*/
@Override
public void run() {
var beans = 0;
while (jar.takeBean()) {
beans = beans + 1;
LOGGER.info("{} took a bean.", name);
}
LOGGER.info("{} took {} beans.", name, beans);
}
}

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mutex/src/test/java/com/iluwatar/mutex/AppTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
/**
* Application Test Entrypoint
*/
class AppTest {
@Test
void shouldExecuteApplicationWithoutException() {
assertDoesNotThrow(() -> App.main(new String[]{}));
}
}

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mutex/src/test/java/com/iluwatar/mutex/JarTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
import static org.junit.jupiter.api.Assertions.assertFalse;
import java.util.stream.IntStream;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
/**
* Test case for taking beans from a Jar
*/
public class JarTest {
@Test
public void testTakeBeans() {
var mutex = new Mutex();
var jar = new Jar(10, mutex);
IntStream.range(0, 10).mapToObj(i -> jar.takeBean()).forEach(Assertions::assertTrue);
assertFalse(jar.takeBean());
}
}

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mutex/src/test/java/com/iluwatar/mutex/MutexTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.mutex;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.fail;
import org.junit.jupiter.api.Test;
/**
* Test case for acquiring and releasing a Mutex
*/
public class MutexTest {
@Test
public void acquireReleaseTest() {
var mutex = new Mutex();
assertNull(mutex.getOwner());
try {
mutex.acquire();
assertEquals(mutex.getOwner(), Thread.currentThread());
} catch (InterruptedException e) {
fail(e.toString());
}
mutex.release();
assertNull(mutex.getOwner());
}
}

2
pom.xml
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@ -141,8 +141,6 @@
<module>module</module>
<module>monad</module>
<module>mute-idiom</module>
<module>mutex</module>
<module>semaphore</module>
<module>hexagonal</module>
<module>abstract-document</module>
<module>aggregator-microservices</module>

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semaphore/README.md
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---
layout: pattern
title: Semaphore
folder: semaphore
permalink: /patterns/semaphore/
categories: Concurrency
tags:
- Performance
---
## Also known as
Counting Semaphore
## Intent
Create a lock which mediates access to a pool of resources.
Only a limited number of threads, specified at the creation
of the semaphore, can access the resources at any given time.
A semaphore which only allows one concurrent access to a resource
is called a binary semaphore.
## Class diagram
![alt text](./etc/semaphore.png "Semaphore")
## Applicability
Use a Semaphore when
* You have a pool of resources to allocate to different threads
* Concurrent access to a resource could lead to a race condition
## Credits
* [Semaphore(programming)] (http://en.wikipedia.org/wiki/Semaphore_(programming))
* [Semaphores] (http://tutorials.jenkov.com/java-concurrency/semaphores.html)

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@startuml
package com.iluwatar.semaphore {
class App {
+ App()
+ main(args : String[]) {static}
}
class Fruit {
- type : FruitType
+ Fruit(type : FruitType)
+ getType() : FruitType
+ toString() : String
}
enum FruitType {
+ APPLE {static}
+ LEMON {static}
+ ORANGE {static}
+ valueOf(name : String) : FruitType {static}
+ values() : FruitType[] {static}
}
class FruitBowl {
- fruit : List<Fruit>
+ FruitBowl()
+ countFruit() : int
+ put(f : Fruit)
+ take() : Fruit
+ toString() : String
}
class FruitShop {
- available : boolean[]
- bowls : FruitBowl[]
- semaphore : Semaphore
+ FruitShop()
+ countFruit() : int
+ returnBowl(bowl : FruitBowl)
+ takeBowl() : FruitBowl
}
interface Lock {
+ acquire() {abstract}
+ release() {abstract}
}
class Semaphore {
- counter : int
- licenses : int
+ Semaphore(licenses : int)
+ acquire()
+ getAvailableLicenses() : int
+ getNumLicenses() : int
+ release()
}
}
FruitType ..+ Fruit
Fruit --> "-type" FruitType
FruitShop --> "-semaphore" Semaphore
FruitBowl --> "-fruit" Fruit
Semaphore ..|> Lock
@enduml

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semaphore/pom.xml
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<?xml version="1.0"?>
<!--
The MIT License
Copyright © 2014-2019 Ilkka Seppälä
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
-->
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId>
<version>1.24.0-SNAPSHOT</version>
</parent>
<artifactId>semaphore</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<configuration>
<archive>
<manifest>
<mainClass>com.iluwatar.semaphore.App</mainClass>
</manifest>
</archive>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

50
semaphore/src/main/java/com/iluwatar/semaphore/App.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
/**
* A Semaphore mediates access by a group of threads to a pool of resources.
*
* <p>In this example a group of customers are taking fruit from a fruit shop. There is a bowl each
* of apples, oranges and lemons. Only one customer can access a bowl simultaneously. A Semaphore is
* used to indicate how many resources are currently available and must be acquired in order for a
* bowl to be given to a customer. Customers continually try to take fruit until there is no fruit
* left in the shop.
*/
public class App {
/**
* main method.
*/
public static void main(String[] args) {
var shop = new FruitShop();
new Customer("Peter", shop).start();
new Customer("Paul", shop).start();
new Customer("Mary", shop).start();
new Customer("John", shop).start();
new Customer("Ringo", shop).start();
new Customer("George", shop).start();
}
}

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semaphore/src/main/java/com/iluwatar/semaphore/Customer.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A Customer attempts to repeatedly take Fruit from the FruitShop by taking Fruit from FruitBowl
* instances.
*/
public class Customer extends Thread {
private static final Logger LOGGER = LoggerFactory.getLogger(Customer.class);
/**
* Name of the Customer.
*/
private final String name;
/**
* The FruitShop he is using.
*/
private final FruitShop fruitShop;
/**
* Their bowl of Fruit.
*/
private final FruitBowl fruitBowl;
/**
* Customer constructor.
*/
public Customer(String name, FruitShop fruitShop) {
this.name = name;
this.fruitShop = fruitShop;
this.fruitBowl = new FruitBowl();
}
/**
* The Customer repeatedly takes Fruit from the FruitShop until no Fruit remains.
*/
public void run() {
while (fruitShop.countFruit() > 0) {
var bowl = fruitShop.takeBowl();
if (bowl != null) {
var fruit = bowl.take();
if (fruit != null) {
LOGGER.info("{} took an {}", name, fruit);
fruitBowl.put(fruit);
fruitShop.returnBowl(bowl);
}
}
}
LOGGER.info("{} took {}", name, fruitBowl);
}
}

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@ -1,64 +0,0 @@
/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
/**
* Fruit is a resource stored in a FruitBowl.
*/
public class Fruit {
/**
* Enumeration of Fruit Types.
*/
public enum FruitType {
ORANGE, APPLE, LEMON
}
private final FruitType type;
public Fruit(FruitType type) {
this.type = type;
}
public FruitType getType() {
return type;
}
/**
* toString method.
*/
public String toString() {
switch (type) {
case ORANGE:
return "Orange";
case APPLE:
return "Apple";
case LEMON:
return "Lemon";
default:
return "";
}
}
}

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semaphore/src/main/java/com/iluwatar/semaphore/FruitBowl.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
import java.util.ArrayList;
import java.util.List;
/**
* A FruitBowl contains Fruit.
*/
public class FruitBowl {
private final List<Fruit> fruit = new ArrayList<>();
/**
* Returns the amount of fruits left in bowl.
*
* @return The amount of Fruit left in the bowl.
*/
public int countFruit() {
return fruit.size();
}
/**
* Put an item of Fruit into the bowl.
*
* @param f fruit
*/
public void put(Fruit f) {
fruit.add(f);
}
/**
* Take an item of Fruit out of the bowl.
*
* @return The Fruit taken out of the bowl, or null if empty.
*/
public Fruit take() {
if (fruit.isEmpty()) {
return null;
} else {
return fruit.remove(0);
}
}
/**
* toString method.
*/
public String toString() {
var apples = 0;
var oranges = 0;
var lemons = 0;
for (var f : fruit) {
switch (f.getType()) {
case APPLE:
apples++;
break;
case ORANGE:
oranges++;
break;
case LEMON:
lemons++;
break;
default:
}
}
return apples + " Apples, " + oranges + " Oranges, and " + lemons + " Lemons";
}
}

120
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
/**
* A FruitShop contains three FruitBowl instances and controls access to them.
*/
public class FruitShop {
/**
* The FruitBowl instances stored in the class.
*/
private final FruitBowl[] bowls = {
new FruitBowl(),
new FruitBowl(),
new FruitBowl()
};
/**
* Access flags for each of the FruitBowl instances.
*/
private final boolean[] available = {
true,
true,
true
};
/**
* The Semaphore that controls access to the class resources.
*/
private final Semaphore semaphore;
/**
* FruitShop constructor.
*/
public FruitShop() {
for (var i = 0; i < 100; i++) {
bowls[0].put(new Fruit(Fruit.FruitType.APPLE));
bowls[1].put(new Fruit(Fruit.FruitType.ORANGE));
bowls[2].put(new Fruit(Fruit.FruitType.LEMON));
}
semaphore = new Semaphore(3);
}
/**
* Returns the amount of fruits left in shop.
*
* @return The amount of Fruit left in the shop.
*/
public synchronized int countFruit() {
return bowls[0].countFruit() + bowls[1].countFruit() + bowls[2].countFruit();
}
/**
* Method called by Customer to get a FruitBowl from the shop. This method will try to acquire the
* Semaphore before returning the first available FruitBowl.
*/
public synchronized FruitBowl takeBowl() {
FruitBowl bowl = null;
try {
semaphore.acquire();
if (available[0]) {
bowl = bowls[0];
available[0] = false;
} else if (available[1]) {
bowl = bowls[1];
available[1] = false;
} else if (available[2]) {
bowl = bowls[2];
available[2] = false;
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
semaphore.release();
}
return bowl;
}
/**
* Method called by a Customer instance to return a FruitBowl to the shop. This method releases
* the Semaphore, making the FruitBowl available to another Customer.
*/
public synchronized void returnBowl(FruitBowl bowl) {
if (bowl == bowls[0]) {
available[0] = true;
} else if (bowl == bowls[1]) {
available[1] = true;
} else if (bowl == bowls[2]) {
available[2] = true;
}
}
}

35
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
/**
* Lock is an interface for a lock which can be acquired and released.
*/
public interface Lock {
void acquire() throws InterruptedException;
void release();
}

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@ -1,77 +0,0 @@
/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
/**
* Semaphore is an implementation of a semaphore lock.
*/
public class Semaphore implements Lock {
private final int licenses;
/**
* The number of concurrent resource accesses which are allowed.
*/
private int counter;
public Semaphore(int licenses) {
this.licenses = licenses;
this.counter = licenses;
}
/**
* Returns the number of licenses managed by the Semaphore.
*/
public int getNumLicenses() {
return licenses;
}
/**
* Returns the number of available licenses.
*/
public int getAvailableLicenses() {
return counter;
}
/**
* Method called by a thread to acquire the lock. If there are no resources available this will
* wait until the lock has been released to re-attempt the acquire.
*/
public synchronized void acquire() throws InterruptedException {
while (counter == 0) {
wait();
}
counter = counter - 1;
}
/**
* Method called by a thread to release the lock.
*/
public synchronized void release() {
if (counter < licenses) {
counter = counter + 1;
notify();
}
}
}

39
semaphore/src/test/java/com/iluwatar/semaphore/AppTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
/**
* Application Test Entrypoint
*/
class AppTest {
@Test
void shouldExecuteWithoutException() {
assertDoesNotThrow(() -> App.main(new String[]{}));
}
}

55
semaphore/src/test/java/com/iluwatar/semaphore/FruitBowlTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;
import org.junit.jupiter.api.Test;
/**
* Test taking from and putting Fruit into a FruitBowl
*/
public class FruitBowlTest {
@Test
public void fruitBowlTest() {
var fbowl = new FruitBowl();
assertEquals(0, fbowl.countFruit());
for (var i = 1; i <= 10; i++) {
fbowl.put(new Fruit(Fruit.FruitType.LEMON));
assertEquals(i, fbowl.countFruit());
}
for (var i = 9; i >= 0; i--) {
assertNotNull(fbowl.take());
assertEquals(i, fbowl.countFruit());
}
assertNull(fbowl.take());
}
}

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semaphore/src/test/java/com/iluwatar/semaphore/SemaphoreTest.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.semaphore;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.fail;
import org.junit.jupiter.api.Test;
/**
* Test case for acquiring and releasing a Semaphore
*/
public class SemaphoreTest {
@Test
public void acquireReleaseTest() {
var sphore = new Semaphore(3);
assertEquals(3, sphore.getAvailableLicenses());
for (var i = 2; i >= 0; i--) {
try {
sphore.acquire();
assertEquals(i, sphore.getAvailableLicenses());
} catch (InterruptedException e) {
fail(e.toString());
}
}
for (var i = 1; i <= 3; i++) {
sphore.release();
assertEquals(i, sphore.getAvailableLicenses());
}
sphore.release();
assertEquals(3, sphore.getAvailableLicenses());
}
}