Introduce reference support submodule

pom.xml

@@ -69,6 +69,7 @@
         <module>io</module>
         <module>net</module>
         <module>os</module>
+        <module>ref</module>
         <module>version</module>
         <module>vertx-context</module>
     </modules>

ref/pom.xml

@@ -0,0 +1,49 @@
+<?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>
+
+    <parent>
+        <groupId>io.smallrye.common</groupId>
+        <artifactId>smallrye-common-parent</artifactId>
+        <version>1.10.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>smallrye-common-ref</artifactId>
+
+    <name>SmallRye Common: References</name>
+
+    <dependencies>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>smallrye-common-constraint</artifactId>
+        </dependency>
+    </dependencies>
+
+    <profiles>
+        <profile>
+            <id>coverage</id>
+            <properties>
+                <argLine>@{jacocoArgLine}</argLine>
+            </properties>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.jacoco</groupId>
+                        <artifactId>jacoco-maven-plugin</artifactId>
+                        <executions>
+                            <execution>
+                                <id>report</id>
+                                <phase>verify</phase>
+                                <goals>
+                                    <goal>report</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
+</project>

ref/src/main/java/io/smallrye/common/ref/CleanerReference.java

@@ -0,0 +1,37 @@
+package io.smallrye.common.ref;
+
+import java.util.Collections;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A special version of {@link PhantomReference} that is strongly retained until it is reaped by the collection thread.
+ */
+public class CleanerReference<T, A> extends PhantomReference<T, A> {
+    private static final Set<CleanerReference<?, ?>> set = Collections
+            .newSetFromMap(new ConcurrentHashMap<CleanerReference<?, ?>, Boolean>());
+
+    /**
+     * Construct a new instance with a reaper.
+     *
+     * @param referent the referent
+     * @param attachment the attachment
+     * @param reaper the reaper to use
+     */
+    public CleanerReference(final T referent, final A attachment, final Reaper<T, A> reaper) {
+        super(referent, attachment, reaper);
+        set.add(this);
+    }
+
+    void clean() {
+        set.remove(this);
+    }
+
+    public final int hashCode() {
+        return super.hashCode();
+    }
+
+    public final boolean equals(final Object obj) {
+        return super.equals(obj);
+    }
+}

ref/src/main/java/io/smallrye/common/ref/PhantomReference.java

@@ -0,0 +1,59 @@
+package io.smallrye.common.ref;
+
+import java.lang.ref.ReferenceQueue;
+
+/**
+ * A reapable phantom reference with an attachment. If a {@link Reaper} is given, then it will be used to asynchronously
+ * clean up the referent.
+ *
+ * @param <T> the reference value type
+ * @param <A> the attachment type
+ *
+ * @see java.lang.ref.PhantomReference
+ */
+public class PhantomReference<T, A> extends java.lang.ref.PhantomReference<T> implements Reference<T, A>, Reapable<T, A> {
+    private final A attachment;
+    private final Reaper<T, A> reaper;
+
+    /**
+     * Construct a new instance with an explicit reference queue.
+     *
+     * @param referent the referent
+     * @param attachment the attachment
+     * @param q the reference queue to use
+     */
+    public PhantomReference(final T referent, final A attachment, final ReferenceQueue<? super T> q) {
+        super(referent, q);
+        this.attachment = attachment;
+        reaper = null;
+    }
+
+    /**
+     * Construct a new instance with a reaper.
+     *
+     * @param referent the referent
+     * @param attachment the attachment
+     * @param reaper the reaper to use
+     */
+    public PhantomReference(final T referent, final A attachment, final Reaper<T, A> reaper) {
+        super(referent, References.ReaperThread.REAPER_QUEUE);
+        this.reaper = reaper;
+        this.attachment = attachment;
+    }
+
+    public A getAttachment() {
+        return attachment;
+    }
+
+    public Type getType() {
+        return Type.PHANTOM;
+    }
+
+    public Reaper<T, A> getReaper() {
+        return reaper;
+    }
+
+    public String toString() {
+        return "phantom reference";
+    }
+}

ref/src/main/java/io/smallrye/common/ref/Reapable.java

@@ -0,0 +1,17 @@
+package io.smallrye.common.ref;
+
+/**
+ * A reference which is reapable (can be automatically collected).
+ *
+ * @param <T> the reference type
+ * @param <A> the reference attachment type
+ */
+interface Reapable<T, A> {
+
+    /**
+     * Get the associated reaper.
+     *
+     * @return the reaper
+     */
+    Reaper<T, A> getReaper();
+}

ref/src/main/java/io/smallrye/common/ref/Reaper.java

@@ -0,0 +1,17 @@
+package io.smallrye.common.ref;
+
+/**
+ * A cleaner for a dead object.
+ *
+ * @param <T> the reference type
+ * @param <A> the reference attachment type
+ */
+public interface Reaper<T, A> {
+
+    /**
+     * Perform the cleanup action for a reference.
+     *
+     * @param reference the reference
+     */
+    void reap(Reference<T, A> reference);
+}

ref/src/main/java/io/smallrye/common/ref/Reference.java

@@ -0,0 +1,135 @@
+package io.smallrye.common.ref;
+
+import java.util.EnumSet;
+
+/**
+ * An enhanced reference type with a type-safe attachment.
+ *
+ * @param <T> the reference value type
+ * @param <A> the attachment type
+ *
+ * @see java.lang.ref.Reference
+ */
+public interface Reference<T, A> {
+
+    /**
+     * Get the value, or {@code null} if the reference has been cleared.
+     *
+     * @return the value
+     */
+    T get();
+
+    /**
+     * Get the attachment, if any.
+     *
+     * @return the attachment
+     */
+    A getAttachment();
+
+    /**
+     * Clear the reference.
+     */
+    void clear();
+
+    /**
+     * Get the type of the reference.
+     *
+     * @return the type
+     */
+    Type getType();
+
+    /**
+     * A reference type.
+     *
+     * @apiviz.exclude
+     */
+    enum Type {
+
+        /**
+         * A strong reference.
+         */
+        STRONG,
+        /**
+         * A weak reference.
+         */
+        WEAK,
+        /**
+         * A phantom reference.
+         */
+        PHANTOM,
+        /**
+         * A soft reference.
+         */
+        SOFT,
+        /**
+         * A {@code null} reference.
+         */
+        NULL,
+        ;
+
+        private static final int fullSize = values().length;
+
+        /**
+         * Determine whether the given set is fully populated (or "full"), meaning it contains all possible values.
+         *
+         * @param set the set
+         *
+         * @return {@code true} if the set is full, {@code false} otherwise
+         */
+        public static boolean isFull(final EnumSet<Type> set) {
+            return set != null && set.size() == fullSize;
+        }
+
+        /**
+         * Determine whether this instance is equal to one of the given instances.
+         *
+         * @param v1 the first instance
+         *
+         * @return {@code true} if one of the instances matches this one, {@code false} otherwise
+         */
+        public boolean in(final Type v1) {
+            return this == v1;
+        }
+
+        /**
+         * Determine whether this instance is equal to one of the given instances.
+         *
+         * @param v1 the first instance
+         * @param v2 the second instance
+         *
+         * @return {@code true} if one of the instances matches this one, {@code false} otherwise
+         */
+        public boolean in(final Type v1, final Type v2) {
+            return this == v1 || this == v2;
+        }
+
+        /**
+         * Determine whether this instance is equal to one of the given instances.
+         *
+         * @param v1 the first instance
+         * @param v2 the second instance
+         * @param v3 the third instance
+         *
+         * @return {@code true} if one of the instances matches this one, {@code false} otherwise
+         */
+        public boolean in(final Type v1, final Type v2, final Type v3) {
+            return this == v1 || this == v2 || this == v3;
+        }
+
+        /**
+         * Determine whether this instance is equal to one of the given instances.
+         *
+         * @param values the possible values
+         *
+         * @return {@code true} if one of the instances matches this one, {@code false} otherwise
+         */
+        public boolean in(final Type... values) {
+            if (values != null)
+                for (Type value : values) {
+                    if (this == value)
+                        return true;
+                }
+            return false;
+        }
+    }
+}