Allow reaper threads to be started at run time

Author: dmlloyd

ref/pom.xml

@@ -17,6 +17,10 @@
             <groupId>${project.groupId}</groupId>
             <artifactId>smallrye-common-constraint</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.graalvm.sdk</groupId>
+            <artifactId>graal-sdk</artifactId>
+        </dependency>
     </dependencies>
 
     <build>

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

@@ -36,7 +36,7 @@ public PhantomReference(final T referent, final A attachment, final ReferenceQue
      * @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);
+        super(referent, References.ReaperThread.getReaperQueue());
         this.reaper = reaper;
         this.attachment = attachment;
     }

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

@@ -6,6 +6,8 @@
 import java.security.PrivilegedAction;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import org.graalvm.nativeimage.ImageInfo;
+
 import io.smallrye.common.constraint.Assert;
 
 /**
@@ -17,27 +19,47 @@ private References() {
 
     private static final Reference<?, ?> NULL = new StrongReference<>(null);
 
-    static final class ReaperThread extends Thread {
+    static final class BuildTimeHolder {
         static final ReferenceQueue<Object> REAPER_QUEUE = new ReferenceQueue<Object>();
+    }
+
+    static final class ReaperThread extends Thread {
+        static ReferenceQueue<Object> getReaperQueue() {
+            return BuildTimeHolder.REAPER_QUEUE;
+        }
 
         static {
-            final AtomicInteger cnt = new AtomicInteger(1);
-            final PrivilegedAction<Void> action = () -> {
-                final ReaperThread thr = new ReaperThread();
-                thr.setName("Reference Reaper #" + cnt.getAndIncrement());
-                thr.setDaemon(true);
-                thr.start();
-                return null;
-            };
-            for (int i = 0; i < 3; i++) {
-                doPrivileged(action);
+            if (isBuildTime()) {
+                // do nothing (class should be reinitialized)
+            } else {
+                final AtomicInteger cnt = new AtomicInteger(1);
+                final PrivilegedAction<Void> action = () -> startThreadAction(cnt.getAndIncrement());
+                for (int i = 0; i < 3; i++) {
+                    doPrivileged(action);
+                }
+            }
+        }
+
+        private static boolean isBuildTime() {
+            try {
+                return ImageInfo.inImageBuildtimeCode();
+            } catch (Throwable ignored) {
+                return false;
             }
         }
 
+        private static Void startThreadAction(int id) {
+            final ReaperThread thr = new ReaperThread();
+            thr.setName("Reference Reaper #" + id);
+            thr.setDaemon(true);
+            thr.start();
+            return null;
+        }
+
         public void run() {
             for (;;)
                 try {
-                    final java.lang.ref.Reference<?> ref = REAPER_QUEUE.remove();
+                    final java.lang.ref.Reference<?> ref = ReaperThread.getReaperQueue().remove();
                     if (ref instanceof CleanerReference) {
                         ((CleanerReference<?, ?>) ref).clean();
                     }

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

@@ -55,7 +55,7 @@ public SoftReference(final T referent, final A attachment, final ReferenceQueue<
      * @param reaper the reaper to use
      */
     public SoftReference(final T referent, final A attachment, final Reaper<T, A> reaper) {
-        super(referent, References.ReaperThread.REAPER_QUEUE);
+        super(referent, References.ReaperThread.getReaperQueue());
         this.reaper = reaper;
         this.attachment = attachment;
     }

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

@@ -55,7 +55,7 @@ public WeakReference(final T referent, final A attachment, final ReferenceQueue<
      * @param reaper the reaper to use
      */
     public WeakReference(final T referent, final A attachment, final Reaper<T, A> reaper) {
-        super(referent, References.ReaperThread.REAPER_QUEUE);
+        super(referent, References.ReaperThread.getReaperQueue());
         this.attachment = attachment;
         this.reaper = reaper;
     }