diff --git a/guarded-suspension/README.md b/guarded-suspension/README.md index 01c03f192..35044f9b2 100644 --- a/guarded-suspension/README.md +++ b/guarded-suspension/README.md @@ -10,12 +10,12 @@ tags: --- ## Intent -Use Guareded suspension pattern to handle a situation when you want to execute a method on object which is not in a proper state. +Use Guarded suspension pattern to handle a situation when you want to execute a method on object which is not in a proper state. ![Guarded Suspension diagram](./etc/guarded-suspension.png) ## Applicability -Use Guareded Suspension pattern when: - -* the developer knows that the method execution will be blocked for a finite period of time +Use Guarded Suspension pattern when the developer knows that the method execution will be blocked for a finite period of time +## Related patterns +* Balking diff --git a/guarded-suspension/etc/guarded-suspension.png b/guarded-suspension/etc/guarded-suspension.png index db962e539..bd3fa5661 100644 Binary files a/guarded-suspension/etc/guarded-suspension.png and b/guarded-suspension/etc/guarded-suspension.png differ diff --git a/guarded-suspension/pom.xml b/guarded-suspension/pom.xml index 9e44d410b..e3a13f2c8 100644 --- a/guarded-suspension/pom.xml +++ b/guarded-suspension/pom.xml @@ -38,6 +38,7 @@ junit junit + test \ No newline at end of file diff --git a/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/App.java b/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/App.java new file mode 100644 index 000000000..8747c84e5 --- /dev/null +++ b/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/App.java @@ -0,0 +1,76 @@ +/** + * The MIT License + * Copyright (c) 2014 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. + */ +/** + * Guarded-suspension is a concurrent design pattern for handling situation when to execute some action we need + * condition to be satisfied. + *

+ * Implementation is based on GuardedQueue, which has two methods: get and put, + * the condition is that we cannot get from empty queue so when thread attempt + * to break the condition we invoke Object's wait method on him and when other thread put an element + * to the queue he notify the waiting one that now he can get from queue. + */ +package com.iluwatar.guarded.suspension; + +import java.util.concurrent.ExecutorService; +import java.util.concurrent.Executors; +import java.util.concurrent.TimeUnit; + +/** + * Created by robertt240 on 1/26/17. + */ +public class App { + /** + * Example pattern execution + * + * @param args - command line args + */ + public static void main(String[] args) { + GuardedQueue guardedQueue = new GuardedQueue(); + ExecutorService executorService = Executors.newFixedThreadPool(3); + + //here we create first thread which is supposed to get from guardedQueue + executorService.execute(() -> { + guardedQueue.get(); + } + ); + + //here we wait two seconds to show that the thread which is trying to get from guardedQueue will be waiting + try { + Thread.sleep(2000); + } catch (InterruptedException e) { + e.printStackTrace(); + } + //now we execute second thread which will put number to guardedQueue and notify first thread that it could get + executorService.execute(() -> { + guardedQueue.put(20); + } + ); + executorService.shutdown(); + try { + executorService.awaitTermination(30, TimeUnit.SECONDS); + } catch (InterruptedException e) { + e.printStackTrace(); + } + } + +} diff --git a/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java b/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java index 47939141f..89b330bfb 100644 --- a/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java +++ b/guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java @@ -31,7 +31,7 @@ import java.util.Queue; public class GuardedQueue { private static final Logger LOGGER = LoggerFactory.getLogger(GuardedQueue.class); - private Queue sourceList; + private final Queue sourceList; public GuardedQueue() { this.sourceList = new LinkedList<>(); @@ -49,7 +49,7 @@ public class GuardedQueue { e.printStackTrace(); } } - + LOGGER.info("getting"); return sourceList.peek(); } @@ -57,9 +57,9 @@ public class GuardedQueue { * @param e number which we want to put to our queue */ public synchronized void put(Integer e) { + LOGGER.info("putting"); sourceList.add(e); - notify(); LOGGER.info("notifying"); - + notify(); } } diff --git a/guarded-suspension/src/test/java/com/iluwatar/guarded/suspension/GuardedQueueTest.java b/guarded-suspension/src/test/java/com/iluwatar/guarded/suspension/GuardedQueueTest.java index 45251acbf..41eaccd49 100644 --- a/guarded-suspension/src/test/java/com/iluwatar/guarded/suspension/GuardedQueueTest.java +++ b/guarded-suspension/src/test/java/com/iluwatar/guarded/suspension/GuardedQueueTest.java @@ -47,4 +47,12 @@ public class GuardedQueueTest { Assert.assertEquals(Integer.valueOf(10), value); } + @Test + public void testPut() { + GuardedQueue g = new GuardedQueue(); + g.put(12); + Assert.assertEquals(Integer.valueOf(12), g.get()); + + } + } \ No newline at end of file diff --git a/pom.xml b/pom.xml index 5ddd3bf98..d2ea715a7 100644 --- a/pom.xml +++ b/pom.xml @@ -121,7 +121,7 @@ factory-kit feature-toggle value-object - module + module monad mute-idiom mutex @@ -134,6 +134,8 @@ event-asynchronous queue-load-leveling object-mother + guarded-suspension +