Ensure that phantom references are enqueued to reference queue

2 files changed, 7 insertions, 3 deletions

diff --git a/jdisc_core/src/main/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdog.java b/jdisc_core/src/main/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdog.java
index 90e2049a868..c6355c93648 100644
--- a/jdisc_core/src/main/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdog.java
+++ b/jdisc_core/src/main/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdog.java
@@ -67,7 +67,7 @@ class ActiveContainerDeactivationWatchdog implements ActiveContainerMetrics, Aut
                                            WATCHDOG_FREQUENCY.getSeconds(),
                                            WATCHDOG_FREQUENCY.getSeconds(),
                                            TimeUnit.SECONDS);
-        this.scheduler.scheduleAtFixedRate(System::gc,
+        this.scheduler.scheduleAtFixedRate(ActiveContainerDeactivationWatchdog::triggerGc,
                                            GC_TRIGGER_FREQUENCY.getSeconds(),
                                            GC_TRIGGER_FREQUENCY.getSeconds(),
                                            TimeUnit.SECONDS);
@@ -121,6 +121,11 @@ class ActiveContainerDeactivationWatchdog implements ActiveContainerMetrics, Aut
         }
     }
 
+    private static void triggerGc() {
+        System.gc();
+        System.runFinalization(); // this is required to trigger enqueuing of phantom references on some Linux systems
+    }
+
     private void enforceDestructionOfGarbageCollectedContainers() {
         ActiveContainerPhantomReference reference;
         while ((reference = (ActiveContainerPhantomReference) garbageCollectedContainers.poll()) != null) {
diff --git a/jdisc_core/src/test/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdogTest.java b/jdisc_core/src/test/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdogTest.java
index 05207728c88..a618b82c5ec 100644
--- a/jdisc_core/src/test/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdogTest.java
+++ b/jdisc_core/src/test/java/com/yahoo/jdisc/core/ActiveContainerDeactivationWatchdogTest.java
@@ -6,7 +6,6 @@ import com.yahoo.jdisc.ResourceReference;
 import com.yahoo.jdisc.statistics.ActiveContainerMetrics;
 import com.yahoo.jdisc.test.TestDriver;
 import com.yahoo.test.ManualClock;
-import org.junit.Ignore;
 import org.junit.Test;
 
 import java.lang.ref.WeakReference;
@@ -69,7 +68,6 @@ public class ActiveContainerDeactivationWatchdogTest {
     }
 
     @Test
-    @Ignore("JVM does not give any guarantee when phantom references will be enqueued to reference queues")
     public void deactivated_container_destructed_if_its_reference_counter_is_nonzero() {
         ExecutorMock executor = new ExecutorMock();
         ActiveContainerDeactivationWatchdog watchdog =
@@ -87,6 +85,7 @@ public class ActiveContainerDeactivationWatchdogTest {
         WeakReference<ActiveContainer> containerWeakReference = new WeakReference<>(container);
         container = null; // make container instance collectable by GC
         System.gc();
+        System.runFinalization(); // this is required to trigger enqueuing of phantom references on some Linux systems
 
         assertNull("Container is not GCed - probably because the watchdog has a concrete reference to it",
                    containerWeakReference.get());