Added LLD projects

distributed-cache/.idea/.gitignore

@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml

distributed-cache/.idea/compiler.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <annotationProcessing>
+      <profile name="Maven default annotation processors profile" enabled="true">
+        <sourceOutputDir name="target/generated-sources/annotations" />
+        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
+        <outputRelativeToContentRoot value="true" />
+        <module name="DistributedCache" />
+      </profile>
+    </annotationProcessing>
+  </component>
+</project>

distributed-cache/.idea/jarRepositories.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RemoteRepositoriesConfiguration">
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Central Repository" />
+      <option name="url" value="https://repo.maven.apache.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Maven Central repository" />
+      <option name="url" value="https://repo1.maven.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="jboss.community" />
+      <option name="name" value="JBoss Community repository" />
+      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
+    </remote-repository>
+  </component>
+</project>

distributed-cache/.idea/misc.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" project-jdk-name="11" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

distributed-cache/.idea/uiDesigner.xml

@@ -0,0 +1,124 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Palette2">
+    <group name="Swing">
+      <item class="com.intellij.uiDesigner.HSpacer" tooltip-text="Horizontal Spacer" icon="/com/intellij/uiDesigner/icons/hspacer.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="1" hsize-policy="6" anchor="0" fill="1" />
+      </item>
+      <item class="com.intellij.uiDesigner.VSpacer" tooltip-text="Vertical Spacer" icon="/com/intellij/uiDesigner/icons/vspacer.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="1" anchor="0" fill="2" />
+      </item>
+      <item class="javax.swing.JPanel" icon="/com/intellij/uiDesigner/icons/panel.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JScrollPane" icon="/com/intellij/uiDesigner/icons/scrollPane.png" removable="false" auto-create-binding="false" can-attach-label="true">
+        <default-constraints vsize-policy="7" hsize-policy="7" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JButton" icon="/com/intellij/uiDesigner/icons/button.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="0" fill="1" />
+        <initial-values>
+          <property name="text" value="Button" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JRadioButton" icon="/com/intellij/uiDesigner/icons/radioButton.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="RadioButton" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JCheckBox" icon="/com/intellij/uiDesigner/icons/checkBox.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="CheckBox" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JLabel" icon="/com/intellij/uiDesigner/icons/label.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="0" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="Label" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JTextField" icon="/com/intellij/uiDesigner/icons/textField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JPasswordField" icon="/com/intellij/uiDesigner/icons/passwordField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JFormattedTextField" icon="/com/intellij/uiDesigner/icons/formattedTextField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTextArea" icon="/com/intellij/uiDesigner/icons/textArea.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTextPane" icon="/com/intellij/uiDesigner/icons/textPane.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JEditorPane" icon="/com/intellij/uiDesigner/icons/editorPane.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JComboBox" icon="/com/intellij/uiDesigner/icons/comboBox.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="2" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JTable" icon="/com/intellij/uiDesigner/icons/table.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JList" icon="/com/intellij/uiDesigner/icons/list.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="2" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTree" icon="/com/intellij/uiDesigner/icons/tree.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTabbedPane" icon="/com/intellij/uiDesigner/icons/tabbedPane.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3">
+          <preferred-size width="200" height="200" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JSplitPane" icon="/com/intellij/uiDesigner/icons/splitPane.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3">
+          <preferred-size width="200" height="200" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JSpinner" icon="/com/intellij/uiDesigner/icons/spinner.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JSlider" icon="/com/intellij/uiDesigner/icons/slider.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JSeparator" icon="/com/intellij/uiDesigner/icons/separator.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JProgressBar" icon="/com/intellij/uiDesigner/icons/progressbar.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="0" fill="1" />
+      </item>
+      <item class="javax.swing.JToolBar" icon="/com/intellij/uiDesigner/icons/toolbar.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="0" fill="1">
+          <preferred-size width="-1" height="20" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JToolBar$Separator" icon="/com/intellij/uiDesigner/icons/toolbarSeparator.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="0" anchor="0" fill="1" />
+      </item>
+      <item class="javax.swing.JScrollBar" icon="/com/intellij/uiDesigner/icons/scrollbar.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="0" anchor="0" fill="2" />
+      </item>
+    </group>
+  </component>
+</project>

distributed-cache/.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
+  </component>
+</project>

distributed-cache/DistributedCache.iml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4" />

distributed-cache/Requirements.ME

@@ -0,0 +1,9 @@
+Should allow:
+ 1) listeners on load and evict
+ 2) hot loading elements on startup
+ 3) multiple eviction algorithms like LRU and LFU
+ 4) expiration time
+ 5) multiple fetch algorithms like write back and write through
+ 6) return futures
+ 7) request collapsing
+ 8) Avoid thrashing with rate limiting

distributed-cache/pom.xml

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>interviewready.io</groupId>
+    <artifactId>distributed-cache</artifactId>
+    <version>1.0</version>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>11</source>
+                    <target>11</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.13</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

distributed-cache/src/main/java/Cache.java

@@ -0,0 +1,179 @@
+import events.*;
+import models.*;
+
+import java.time.Duration;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.*;
+import java.util.function.Function;
+
+public class Cache<KEY, VALUE> {
+    private final int maximumSize;
+    private final FetchAlgorithm fetchAlgorithm;
+    private final Duration expiryTime;
+    private final Map<KEY, CompletionStage<Record<KEY, VALUE>>> cache;
+    private final ConcurrentSkipListMap<AccessDetails, List<KEY>> priorityQueue;
+    private final ConcurrentSkipListMap<Long, List<KEY>> expiryQueue;
+    private final DataSource<KEY, VALUE> dataSource;
+    private final List<Event<KEY, VALUE>> eventQueue;
+    private final ExecutorService[] executorPool;
+    private final Timer timer;
+
+    protected Cache(final int maximumSize,
+                    final Duration expiryTime,
+                    final FetchAlgorithm fetchAlgorithm,
+                    final EvictionAlgorithm evictionAlgorithm,
+                    final DataSource<KEY, VALUE> dataSource,
+                    final Set<KEY> keysToEagerlyLoad,
+                    final Timer timer,
+                    final int poolSize) {
+        this.expiryTime = expiryTime;
+        this.maximumSize = maximumSize;
+        this.fetchAlgorithm = fetchAlgorithm;
+        this.timer = timer;
+        this.cache = new ConcurrentHashMap<>();
+        this.eventQueue = new CopyOnWriteArrayList<>();
+        this.dataSource = dataSource;
+        this.executorPool = new ExecutorService[poolSize];
+        for (int i = 0; i < poolSize; i++) {
+            executorPool[i] = Executors.newSingleThreadExecutor();
+        }
+        priorityQueue = new ConcurrentSkipListMap<>((first, second) -> {
+            final var accessTimeDifference = (int) (first.getLastAccessTime() - second.getLastAccessTime());
+            if (evictionAlgorithm.equals(EvictionAlgorithm.LRU)) {
+                return accessTimeDifference;
+            } else {
+                final var accessCountDifference = first.getAccessCount() - second.getAccessCount();
+                return accessCountDifference != 0 ? accessCountDifference : accessTimeDifference;
+            }
+        });
+        expiryQueue = new ConcurrentSkipListMap<>();
+        final var eagerLoading = keysToEagerlyLoad.stream()
+                .map(key -> getThreadFor(key, addToCache(key, loadFromDB(dataSource, key))))
+                .toArray(CompletableFuture[]::new);
+        CompletableFuture.allOf(eagerLoading).join();
+    }
+
+    private <U> CompletionStage<U> getThreadFor(KEY key, CompletionStage<U> task) {
+        return CompletableFuture.supplyAsync(() -> task, executorPool[Math.abs(key.hashCode() % executorPool.length)]).thenCompose(Function.identity());
+    }
+
+    public CompletionStage<VALUE> get(KEY key) {
+        return getThreadFor(key, getFromCache(key));
+    }
+
+    public CompletionStage<Void> set(KEY key, VALUE value) {
+        return getThreadFor(key, setInCache(key, value));
+    }
+
+    private CompletionStage<VALUE> getFromCache(KEY key) {
+        final CompletionStage<Record<KEY, VALUE>> result;
+        if (!cache.containsKey(key)) {
+            result = addToCache(key, loadFromDB(dataSource, key));
+        } else {
+            result = cache.get(key).thenCompose(record -> {
+                if (hasExpired(record)) {
+                    priorityQueue.get(record.getAccessDetails()).remove(key);
+                    expiryQueue.get(record.getInsertionTime()).remove(key);
+                    eventQueue.add(new Eviction<>(record, Eviction.Type.EXPIRY, timer.getCurrentTime()));
+                    return addToCache(key, loadFromDB(dataSource, key));
+                } else {
+                    return CompletableFuture.completedFuture(record);
+                }
+            });
+        }
+        return result.thenApply(record -> {
+            priorityQueue.get(record.getAccessDetails()).remove(key);
+            final AccessDetails updatedAccessDetails = record.getAccessDetails().update(timer.getCurrentTime());
+            priorityQueue.putIfAbsent(updatedAccessDetails, new CopyOnWriteArrayList<>());
+            priorityQueue.get(updatedAccessDetails).add(key);
+            record.setAccessDetails(updatedAccessDetails);
+            return record.getValue();
+        });
+    }
+
+    public CompletionStage<Void> setInCache(KEY key, VALUE value) {
+        CompletionStage<Void> result = CompletableFuture.completedFuture(null);
+        if (cache.containsKey(key)) {
+            result = cache.remove(key)
+                    .thenAccept(oldRecord -> {
+                        priorityQueue.get(oldRecord.getAccessDetails()).remove(key);
+                        expiryQueue.get(oldRecord.getInsertionTime()).remove(key);
+                        if (hasExpired(oldRecord)) {
+                            eventQueue.add(new Eviction<>(oldRecord, Eviction.Type.EXPIRY, timer.getCurrentTime()));
+                        } else {
+                            eventQueue.add(new Update<>(new Record<>(key, value, timer.getCurrentTime()), oldRecord, timer.getCurrentTime()));
+                        }
+                    });
+        }
+        return result.thenCompose(__ -> addToCache(key, CompletableFuture.completedFuture(value))).thenCompose(record -> {
+            final CompletionStage<Void> writeOperation = persistRecord(record);
+            return fetchAlgorithm == FetchAlgorithm.WRITE_THROUGH ? writeOperation : CompletableFuture.completedFuture(null);
+        });
+    }
+
+    private CompletionStage<Record<KEY, VALUE>> addToCache(final KEY key, final CompletionStage<VALUE> valueFuture) {
+        manageEntries();
+        final var recordFuture = valueFuture.thenApply(value -> {
+            final Record<KEY, VALUE> record = new Record<>(key, value, timer.getCurrentTime());
+            expiryQueue.putIfAbsent(record.getInsertionTime(), new CopyOnWriteArrayList<>());
+            expiryQueue.get(record.getInsertionTime()).add(key);
+            priorityQueue.putIfAbsent(record.getAccessDetails(), new CopyOnWriteArrayList<>());
+            priorityQueue.get(record.getAccessDetails()).add(key);
+            return record;
+        });
+        cache.put(key, recordFuture);
+        return recordFuture;
+    }
+
+    private synchronized void manageEntries() {
+        if (cache.size() >= maximumSize) {
+            while (!expiryQueue.isEmpty() && hasExpired(expiryQueue.firstKey())) {
+                final List<KEY> keys = expiryQueue.pollFirstEntry().getValue();
+                for (final KEY key : keys) {
+                    final Record<KEY, VALUE> expiredRecord = cache.remove(key).toCompletableFuture().join();
+                    priorityQueue.remove(expiredRecord.getAccessDetails());
+                    eventQueue.add(new Eviction<>(expiredRecord, Eviction.Type.EXPIRY, timer.getCurrentTime()));
+                }
+            }
+        }
+        if (cache.size() >= maximumSize) {
+            List<KEY> keys = priorityQueue.pollFirstEntry().getValue();
+            while (keys.isEmpty()) {
+                keys = priorityQueue.pollFirstEntry().getValue();
+            }
+            for (final KEY key : keys) {
+                final Record<KEY, VALUE> lowestPriorityRecord = cache.remove(key).toCompletableFuture().join();
+                expiryQueue.get(lowestPriorityRecord.getInsertionTime()).remove(lowestPriorityRecord.getKey());
+                eventQueue.add(new Eviction<>(lowestPriorityRecord, Eviction.Type.REPLACEMENT, timer.getCurrentTime()));
+            }
+        }
+    }
+
+    private CompletionStage<Void> persistRecord(final Record<KEY, VALUE> record) {
+        return dataSource.persist(record.getKey(), record.getValue(), record.getInsertionTime())
+                .thenAccept(__ -> eventQueue.add(new Write<>(record, timer.getCurrentTime())));
+    }
+
+    private boolean hasExpired(final Record<KEY, VALUE> record) {
+        return hasExpired(record.getInsertionTime());
+    }
+
+    private boolean hasExpired(final Long time) {
+        return Duration.ofNanos(timer.getCurrentTime() - time).compareTo(expiryTime) > 0;
+    }
+
+    public List<Event<KEY, VALUE>> getEventQueue() {
+        return eventQueue;
+    }
+
+    private CompletionStage<VALUE> loadFromDB(final DataSource<KEY, VALUE> dataSource, KEY key) {
+        return dataSource.load(key).whenComplete((value, throwable) -> {
+            if (throwable == null) {
+                eventQueue.add(new Load<>(new Record<>(key, value, timer.getCurrentTime()), timer.getCurrentTime()));
+            }
+        });
+    }
+}
+

distributed-cache/src/main/java/CacheBuilder.java

@@ -0,0 +1,75 @@
+import models.EvictionAlgorithm;
+import models.FetchAlgorithm;
+import models.Timer;
+
+import java.time.Duration;
+import java.util.HashSet;
+import java.util.Set;
+
+public class CacheBuilder<KEY, VALUE> {
+    private int maximumSize;
+    private Duration expiryTime;
+    private final Set<KEY> onStartLoad;
+    private EvictionAlgorithm evictionAlgorithm;
+    private FetchAlgorithm fetchAlgorithm;
+    private DataSource<KEY, VALUE> dataSource;
+    private Timer timer;
+    private int poolSize;
+
+    public CacheBuilder() {
+        maximumSize = 1000;
+        expiryTime = Duration.ofDays(365);
+        fetchAlgorithm = FetchAlgorithm.WRITE_THROUGH;
+        evictionAlgorithm = EvictionAlgorithm.LRU;
+        onStartLoad = new HashSet<>();
+        poolSize = 1;
+        timer = new Timer();
+    }
+
+    public CacheBuilder<KEY, VALUE> maximumSize(final int maximumSize) {
+        this.maximumSize = maximumSize;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> expiryTime(final Duration expiryTime) {
+        this.expiryTime = expiryTime;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> loadKeysOnStart(final Set<KEY> keys) {
+        this.onStartLoad.addAll(keys);
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> evictionAlgorithm(final EvictionAlgorithm evictionAlgorithm) {
+        this.evictionAlgorithm = evictionAlgorithm;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> fetchAlgorithm(final FetchAlgorithm fetchAlgorithm) {
+        this.fetchAlgorithm = fetchAlgorithm;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> dataSource(final DataSource<KEY, VALUE> dataSource) {
+        this.dataSource = dataSource;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> timer(final Timer timer) {
+        this.timer = timer;
+        return this;
+    }
+
+    public CacheBuilder<KEY, VALUE> poolSize(final int poolSize) {
+        this.poolSize = poolSize;
+        return this;
+    }
+
+    public Cache<KEY, VALUE> build() {
+        if (dataSource == null) {
+            throw new IllegalArgumentException("No datasource configured");
+        }
+        return new Cache<>(maximumSize, expiryTime, fetchAlgorithm, evictionAlgorithm, dataSource, onStartLoad, timer, poolSize);
+    }
+}

distributed-cache/src/main/java/DataSource.java

@@ -0,0 +1,8 @@
+import java.util.concurrent.CompletionStage;
+
+public interface DataSource<KEY, VALUE> {
+
+    CompletionStage<VALUE> load(KEY key);
+
+    CompletionStage<Void> persist(KEY key, VALUE value, long timestamp);
+}

distributed-cache/src/main/java/events/Event.java

@@ -0,0 +1,37 @@
+package events;
+
+import models.Record;
+
+import java.util.UUID;
+
+public abstract class Event<KEY, VALUE> {
+    private final String id;
+    private final Record<KEY, VALUE> element;
+    private final long timestamp;
+
+    public Event(Record<KEY, VALUE> element, long timestamp) {
+        this.element = element;
+        this.timestamp = timestamp;
+        id = UUID.randomUUID().toString();
+    }
+
+    public String getId() {
+        return id;
+    }
+
+    public Record<KEY, VALUE> getElement() {
+        return element;
+    }
+
+    public long getTimestamp() {
+        return timestamp;
+    }
+
+    @Override
+    public String toString() {
+        return this.getClass().getName() + "{" +
+                "element=" + element +
+                ", timestamp=" + timestamp +
+                "}\n";
+    }
+}

distributed-cache/src/main/java/events/Eviction.java

@@ -0,0 +1,28 @@
+package events;
+
+import models.Record;
+
+public class Eviction<K, V> extends Event<K, V> {
+    private final Type type;
+
+    public Eviction(Record<K, V> element, Type type, long timestamp) {
+        super(element, timestamp);
+        this.type = type;
+    }
+
+    public Type getType() {
+        return type;
+    }
+
+    public enum Type {
+        EXPIRY, REPLACEMENT
+    }
+
+    @Override
+    public String toString() {
+        return "Eviction{" +
+                "type=" + type +
+                ", "+super.toString() +
+                "}\n";
+    }
+}

distributed-cache/src/main/java/events/Load.java

@@ -0,0 +1,10 @@
+package events;
+
+import models.Record;
+
+public class Load<K, V> extends Event<K, V> {
+
+    public Load(Record<K, V> element, long timestamp) {
+        super(element, timestamp);
+    }
+}

distributed-cache/src/main/java/events/Update.java

@@ -0,0 +1,13 @@
+package events;
+
+import models.Record;
+
+public class Update<K, V> extends Event<K, V> {
+
+    private final Record<K, V> previousValue;
+
+    public Update(Record<K, V> element, Record<K, V> previousValue, long timestamp) {
+        super(element, timestamp);
+        this.previousValue = previousValue;
+    }
+}

distributed-cache/src/main/java/events/Write.java

@@ -0,0 +1,10 @@
+package events;
+
+import models.Record;
+
+public class Write<K, V> extends Event<K, V> {
+
+    public Write(Record<K, V> element, long timestamp) {
+        super(element, timestamp);
+    }
+}

distributed-cache/src/main/java/models/AccessDetails.java

@@ -0,0 +1,50 @@
+package models;
+
+import java.util.Objects;
+import java.util.concurrent.atomic.LongAdder;
+
+public class AccessDetails {
+    private final LongAdder accessCount;
+    private long lastAccessTime;
+
+    public AccessDetails(long lastAccessTime) {
+        accessCount = new LongAdder();
+        this.lastAccessTime = lastAccessTime;
+    }
+
+    public long getLastAccessTime() {
+        return lastAccessTime;
+    }
+
+    public int getAccessCount() {
+        return (int) accessCount.longValue();
+    }
+
+    public AccessDetails update(long lastAccessTime) {
+        final AccessDetails accessDetails = new AccessDetails(lastAccessTime);
+        accessDetails.accessCount.add(this.accessCount.longValue() + 1);
+        return accessDetails;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        AccessDetails that = (AccessDetails) o;
+        return lastAccessTime == that.lastAccessTime &&
+                this.getAccessCount() == that.getAccessCount();
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getAccessCount(), lastAccessTime);
+    }
+
+    @Override
+    public String toString() {
+        return "AccessDetails{" +
+                "accessCount=" + accessCount +
+                ", lastAccessTime=" + lastAccessTime +
+                '}';
+    }
+}

distributed-cache/src/main/java/models/EvictionAlgorithm.java

@@ -0,0 +1,5 @@
+package models;
+
+public enum EvictionAlgorithm {
+    LRU, LFU
+}

distributed-cache/src/main/java/models/FetchAlgorithm.java

@@ -0,0 +1,5 @@
+package models;
+
+public enum FetchAlgorithm {
+    WRITE_THROUGH, WRITE_BACK
+}

distributed-cache/src/main/java/models/Record.java

@@ -0,0 +1,46 @@
+package models;
+
+public class Record<KEY, VALUE> {
+    private final KEY key;
+    private final VALUE value;
+    private final long insertionTime;
+    private AccessDetails accessDetails;
+
+    public Record(KEY key, VALUE value, long insertionTime) {
+        this.key = key;
+        this.value = value;
+        this.insertionTime = insertionTime;
+        this.accessDetails = new AccessDetails(insertionTime);
+    }
+
+    public KEY getKey() {
+        return key;
+    }
+
+    public VALUE getValue() {
+        return value;
+    }
+
+    public long getInsertionTime() {
+        return insertionTime;
+    }
+
+    public AccessDetails getAccessDetails() {
+        return accessDetails;
+    }
+
+    public void setAccessDetails(final AccessDetails accessDetails) {
+        this.accessDetails = accessDetails;
+    }
+
+    @Override
+    public String toString() {
+        return "Record{" +
+                "key=" + key +
+                ", value=" + value +
+                ", insertionTime=" + insertionTime +
+                ", accessDetails=" + accessDetails +
+                '}';
+    }
+}
+

distributed-cache/src/main/java/models/Timer.java

@@ -0,0 +1,7 @@
+package models;
+
+public class Timer {
+    public long getCurrentTime() {
+        return System.nanoTime();
+    }
+}

distributed-cache/src/test/java/TestCache.java

@@ -0,0 +1,366 @@
+import events.Eviction;
+import events.Load;
+import events.Update;
+import events.Write;
+import models.EvictionAlgorithm;
+import models.FetchAlgorithm;
+import models.SettableTimer;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.time.Duration;
+import java.util.*;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.stream.Collectors;
+
+public class TestCache {
+
+    private static final String PROFILE_MUMBAI_ENGINEER = "profile_mumbai_engineer", PROFILE_HYDERABAD_ENGINEER = "profile_hyderabad_engineer";
+    private final Map<String, String> dataMap = new ConcurrentHashMap<>();
+    private DataSource<String, String> dataSource;
+    private final Queue<CompletableFuture<Void>> writeOperations = new LinkedList<>();
+    private DataSource<String, String> writeBackDataSource;
+
+    @Before
+    public void setUp() {
+        dataMap.clear();
+        writeOperations.clear();
+        dataMap.put(PROFILE_MUMBAI_ENGINEER, "violet");
+        dataMap.put(PROFILE_HYDERABAD_ENGINEER, "blue");
+        dataSource = new DataSource<>() {
+            @Override
+            public CompletionStage<String> load(String key) {
+                if (dataMap.containsKey(key)) {
+                    return CompletableFuture.completedFuture(dataMap.get(key));
+                } else {
+                    return CompletableFuture.failedStage(new NullPointerException());
+                }
+            }
+
+            @Override
+            public CompletionStage<Void> persist(String key, String value, long timestamp) {
+                dataMap.put(key, value);
+                return CompletableFuture.completedFuture(null);
+            }
+        };
+
+        writeBackDataSource = new DataSource<>() {
+            @Override
+            public CompletionStage<String> load(String key) {
+                if (dataMap.containsKey(key)) {
+                    return CompletableFuture.completedFuture(dataMap.get(key));
+                } else {
+                    return CompletableFuture.failedStage(new NullPointerException());
+                }
+            }
+
+            @Override
+            public CompletionStage<Void> persist(String key, String value, long timestamp) {
+                final CompletableFuture<Void> hold = new CompletableFuture<>();
+                writeOperations.add(hold);
+                return hold.thenAccept(__ -> dataMap.put(key, value));
+            }
+        };
+    }
+
+    private void acceptWrite() {
+        final CompletableFuture<Void> write = writeOperations.poll();
+        if (write != null) {
+            write.complete(null);
+        }
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testCacheConstructionWithoutDataSourceFailure() {
+        new CacheBuilder<>().build();
+    }
+
+    @Test
+    public void testCacheDefaultBehavior() throws ExecutionException, InterruptedException {
+        final var cache = new CacheBuilder<String, String>().dataSource(dataSource).build();
+        Assert.assertNotNull(cache);
+        assert isEqualTo(cache.get(PROFILE_MUMBAI_ENGINEER), "violet");
+        assert cache.get("random")
+                .exceptionally(throwable -> Boolean.TRUE.toString())
+                .thenApply(Boolean::valueOf)
+                .toCompletableFuture()
+                .get();
+        assert isEqualTo(cache.set(PROFILE_MUMBAI_ENGINEER, "brown").thenCompose(__ -> cache.get(PROFILE_MUMBAI_ENGINEER)), "brown");
+        Assert.assertEquals(3, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        assert cache.getEventQueue().get(1) instanceof Update;
+        assert cache.getEventQueue().get(2) instanceof Write;
+    }
+
+    @Test
+    public void Eviction_LRU() {
+        final var maximumSize = 2;
+        final var cache = new CacheBuilder<String, String>()
+                .maximumSize(maximumSize)
+                .evictionAlgorithm(EvictionAlgorithm.LRU)
+                .fetchAlgorithm(FetchAlgorithm.WRITE_BACK)
+                .dataSource(writeBackDataSource).build();
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        for (int i = 0; i < maximumSize; i++) {
+            cache.set("key" + i, "value" + i).toCompletableFuture().join();
+        }
+        Assert.assertEquals(2, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        assert cache.getEventQueue().get(1) instanceof Eviction;
+        final var evictionEvent = (Eviction<String, String>) cache.getEventQueue().get(1);
+        Assert.assertEquals(Eviction.Type.REPLACEMENT, evictionEvent.getType());
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, evictionEvent.getElement().getKey());
+        cache.getEventQueue().clear();
+        final var permutation = new ArrayList<Integer>();
+        for (int i = 0; i < maximumSize; i++) {
+            permutation.add(i);
+        }
+        Collections.shuffle(permutation);
+        for (final int index : permutation) {
+            cache.get("key" + index).toCompletableFuture().join();
+        }
+        for (int i = 0; i < maximumSize; i++) {
+            cache.set("random" + permutation.get(i), "random_value").toCompletableFuture().join();
+            assert cache.getEventQueue().get(i) instanceof Eviction;
+            final var eviction = (Eviction<String, String>) cache.getEventQueue().get(i);
+            Assert.assertEquals(Eviction.Type.REPLACEMENT, eviction.getType());
+            Assert.assertEquals("key" + permutation.get(i), eviction.getElement().getKey());
+        }
+    }
+
+    @Test
+    public void Eviction_LFU() {
+        final var maximumSize = 2;
+        final var cache = new CacheBuilder<String, String>()
+                .maximumSize(maximumSize)
+                .evictionAlgorithm(EvictionAlgorithm.LFU)
+                .fetchAlgorithm(FetchAlgorithm.WRITE_BACK)
+                .dataSource(writeBackDataSource)
+                .build();
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        for (int i = 0; i < maximumSize; i++) {
+            cache.set("key" + i, "value" + i).toCompletableFuture().join();
+        }
+        Assert.assertEquals(2, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        assert cache.getEventQueue().get(1) instanceof Eviction;
+        final var evictionEvent = (Eviction<String, String>) cache.getEventQueue().get(1);
+        Assert.assertEquals(Eviction.Type.REPLACEMENT, evictionEvent.getType());
+        Assert.assertEquals("key0", evictionEvent.getElement().getKey());
+        for (int i = 0; i < maximumSize; i++) {
+            acceptWrite();
+        }
+        final var permutation = new ArrayList<Integer>();
+        for (int i = 0; i < maximumSize; i++) {
+            permutation.add(i);
+        }
+        Collections.shuffle(permutation);
+        for (final int index : permutation) {
+            for (int i = 0; i <= index; i++) {
+                cache.get("key" + index).toCompletableFuture().join();
+            }
+        }
+        cache.getEventQueue().clear();
+        for (int i = 0; i < maximumSize; i++) {
+            cache.set("random" + i, "random_value").toCompletableFuture().join();
+            acceptWrite();
+            for (int j = 0; j <= maximumSize; j++) {
+                cache.get("random" + i).toCompletableFuture().join();
+            }
+            Assert.assertEquals(Eviction.class.getName(), cache.getEventQueue().get(i * 2).getClass().getName());
+            Assert.assertEquals(Write.class.getName(), cache.getEventQueue().get(i * 2 + 1).getClass().getName());
+            final var eviction = (Eviction<String, String>) cache.getEventQueue().get(i * 2);
+            System.out.println(cache.getEventQueue().get(i));
+            Assert.assertEquals(Eviction.Type.REPLACEMENT, eviction.getType());
+            Assert.assertEquals("key" + i, eviction.getElement().getKey());
+        }
+    }
+
+    @Test
+    public void ExpiryOnGet() {
+        final var timer = new SettableTimer();
+        final var startTime = System.nanoTime();
+        final var cache = new CacheBuilder<String, String>().timer(timer).dataSource(dataSource).expiryTime(Duration.ofSeconds(10)).build();
+        timer.setTime(startTime);
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        Assert.assertEquals(1, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, cache.getEventQueue().get(0).getElement().getKey());
+        timer.setTime(startTime + Duration.ofSeconds(10).toNanos() + 1);
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        Assert.assertEquals(3, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(1) instanceof Eviction;
+        assert cache.getEventQueue().get(2) instanceof Load;
+        final var eviction = (Eviction<String, String>) cache.getEventQueue().get(1);
+        Assert.assertEquals(Eviction.Type.EXPIRY, eviction.getType());
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, eviction.getElement().getKey());
+    }
+
+    @Test
+    public void ExpiryOnSet() {
+        final var timer = new SettableTimer();
+        final var startTime = System.nanoTime();
+        final var cache = new CacheBuilder<String, String>().timer(timer).dataSource(dataSource).expiryTime(Duration.ofSeconds(10)).build();
+        timer.setTime(startTime);
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        Assert.assertEquals(1, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, cache.getEventQueue().get(0).getElement().getKey());
+        timer.setTime(startTime + Duration.ofSeconds(10).toNanos() + 1);
+        cache.set(PROFILE_MUMBAI_ENGINEER, "blue").toCompletableFuture().join();
+        Assert.assertEquals(3, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(1) instanceof Eviction;
+        assert cache.getEventQueue().get(2) instanceof Write;
+        final var eviction = (Eviction<String, String>) cache.getEventQueue().get(1);
+        Assert.assertEquals(Eviction.Type.EXPIRY, eviction.getType());
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, eviction.getElement().getKey());
+    }
+
+    @Test
+    public void ExpiryOnEviction() {
+        final var timer = new SettableTimer();
+        final var startTime = System.nanoTime();
+        final var cache = new CacheBuilder<String, String>().maximumSize(2).timer(timer).dataSource(dataSource).expiryTime(Duration.ofSeconds(10)).build();
+        timer.setTime(startTime);
+        cache.get(PROFILE_MUMBAI_ENGINEER).toCompletableFuture().join();
+        cache.get(PROFILE_HYDERABAD_ENGINEER).toCompletableFuture().join();
+        timer.setTime(startTime + Duration.ofSeconds(10).toNanos() + 1);
+        cache.set("randomKey", "randomValue").toCompletableFuture().join();
+        Assert.assertEquals(5, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(2) instanceof Eviction;
+        assert cache.getEventQueue().get(3) instanceof Eviction;
+        assert cache.getEventQueue().get(4) instanceof Write;
+        final var eviction1 = (Eviction<String, String>) cache.getEventQueue().get(2);
+        Assert.assertEquals(Eviction.Type.EXPIRY, eviction1.getType());
+        Assert.assertEquals(PROFILE_MUMBAI_ENGINEER, eviction1.getElement().getKey());
+        final var eviction2 = (Eviction<String, String>) cache.getEventQueue().get(3);
+        Assert.assertEquals(Eviction.Type.EXPIRY, eviction2.getType());
+        Assert.assertEquals(PROFILE_HYDERABAD_ENGINEER, eviction2.getElement().getKey());
+    }
+
+    @Test
+    public void FetchingWriteBack() {
+        final var cache = new CacheBuilder<String, String>()
+                .maximumSize(1)
+                .dataSource(writeBackDataSource)
+                .fetchAlgorithm(FetchAlgorithm.WRITE_BACK)
+                .build();
+        cache.set("randomKey", "randomValue").toCompletableFuture().join();
+        Assert.assertEquals(0, cache.getEventQueue().size());
+        Assert.assertNull(dataMap.get("randomValue"));
+        acceptWrite();
+    }
+
+    @Test
+    public void FetchingWriteThrough() {
+        final var cache = new CacheBuilder<String, String>().dataSource(dataSource).fetchAlgorithm(FetchAlgorithm.WRITE_THROUGH).build();
+        cache.set("randomKey", "randomValue").toCompletableFuture().join();
+        Assert.assertEquals(1, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Write;
+        Assert.assertEquals("randomValue", dataMap.get("randomKey"));
+    }
+
+    @Test
+    public void EagerLoading() {
+        final var eagerlyLoad = new HashSet<String>();
+        eagerlyLoad.add(PROFILE_MUMBAI_ENGINEER);
+        eagerlyLoad.add(PROFILE_HYDERABAD_ENGINEER);
+        final var cache = new CacheBuilder<String, String>()
+                .loadKeysOnStart(eagerlyLoad)
+                .dataSource(dataSource)
+                .build();
+        Assert.assertEquals(2, cache.getEventQueue().size());
+        assert cache.getEventQueue().get(0) instanceof Load;
+        assert cache.getEventQueue().get(1) instanceof Load;
+        cache.getEventQueue().clear();
+        dataMap.clear();
+        isEqualTo(cache.get(PROFILE_MUMBAI_ENGINEER), "violet");
+        isEqualTo(cache.get(PROFILE_HYDERABAD_ENGINEER), "blue");
+        Assert.assertEquals(0, cache.getEventQueue().size());
+    }
+
+    @Test
+    public void RaceConditions() throws ExecutionException, InterruptedException {
+        final var cache = new CacheBuilder<String, String>()
+                .poolSize(8)
+                .dataSource(dataSource).build();
+        final var cacheEntries = new HashMap<String, List<String>>();
+        final var numberOfEntries = 100;
+        final var numberOfValues = 1000;
+        final String[] keyList = new String[numberOfEntries];
+        final Map<String, Integer> inverseMapping = new HashMap<>();
+        for (int entry = 0; entry < numberOfEntries; entry++) {
+            final var key = UUID.randomUUID().toString();
+            keyList[entry] = key;
+            inverseMapping.put(key, entry);
+            cacheEntries.put(key, new ArrayList<>());
+            final var firstValue = UUID.randomUUID().toString();
+            dataMap.put(key, firstValue);
+            cacheEntries.get(key).add(firstValue);
+            for (int value = 0; value < numberOfValues - 1; value++) {
+                cacheEntries.get(key).add(UUID.randomUUID().toString());
+            }
+        }
+        final Random random = new Random();
+        final List<CompletionStage<String>> futures = new ArrayList<>();
+        final List<String> queries = new ArrayList<>();
+        final int[] updates = new int[numberOfEntries];
+        for (int i = 0; i < 1000000; i++) {
+            final var index = random.nextInt(numberOfEntries);
+            final var key = keyList[index];
+            if (Math.random() <= 0.05) {
+                if (updates[index] - 1 < numberOfEntries) {
+                    updates[index]++;
+                }
+                cache.set(key, cacheEntries.get(key).get(updates[index] + 1));
+            } else {
+                queries.add(key);
+                futures.add(cache.get(key));
+            }
+        }
+        final CompletionStage<List<String>> results = CompletableFuture.allOf(futures.toArray(CompletableFuture[]::new))
+                .thenApply(__ -> futures.stream()
+                        .map(CompletionStage::toCompletableFuture)
+                        .map(CompletableFuture::join)
+                        .collect(Collectors.toList()));
+        final int[] currentIndexes = new int[numberOfEntries];
+        final StringBuilder stringBuilder = new StringBuilder();
+        results.thenAccept(values -> {
+            for (int i = 0; i < values.size(); i++) {
+                final var key = queries.get(i);
+                final var possibleValuesForKey = cacheEntries.get(key);
+                final var currentValue = currentIndexes[inverseMapping.get(key)];
+                if (!possibleValuesForKey.get(currentValue).equals(values.get(i))) {
+                    int offset = 1;
+                    while (currentValue + offset < numberOfValues && !possibleValuesForKey.get(currentValue + offset).equals(values.get(i))) {
+                        offset++;
+                    }
+                    if (currentValue + offset == numberOfValues) {
+                        System.out.println(Arrays.stream(stringBuilder.toString().split("\n")).filter(line -> line.contains(key)).collect(Collectors.joining("\n")));
+                        System.err.println(key);
+                        System.err.println(possibleValuesForKey);
+                        System.err.println(possibleValuesForKey.get(currentValue) + " index: " + currentIndexes[inverseMapping.get(key)]);
+                        System.err.println(values.get(i));
+                        throw new IllegalStateException();
+                    }
+                    currentIndexes[inverseMapping.get(key)] += offset;
+                    stringBuilder.append(key).append(" index: ").append(currentIndexes[inverseMapping.get(key)]).append(" ").append(values.get(i)).append('\n');
+                }
+            }
+        }).toCompletableFuture().join();
+    }
+
+    private boolean isEqualTo(CompletionStage<String> future, String value) {
+        return future.thenApply(result -> {
+            if (result.equals(value)) {
+                return true;
+            } else {
+                throw new AssertionError();
+            }
+        }).toCompletableFuture().join();
+    }
+}

distributed-cache/src/test/java/models/SettableTimer.java

@@ -0,0 +1,14 @@
+package models;
+
+public class SettableTimer extends Timer {
+    private long time = -1;
+
+    @Override
+    public long getCurrentTime() {
+        return time == -1 ? System.nanoTime() : time;
+    }
+
+    public void setTime(long time) {
+        this.time = time;
+    }
+}