Hacks to avoid SIGSEGV in tests that call Preferences.setNetworkTableInstance()

lib/src/test/java/com/team2813/lib2813/preferences/IsolatedPreferences.java

@@ -17,7 +17,9 @@
 
 import edu.wpi.first.networktables.NetworkTable;
 import edu.wpi.first.networktables.NetworkTableInstance;
+import edu.wpi.first.networktables.NetworkTableListener;
 import edu.wpi.first.wpilibj.Preferences;
+import java.lang.reflect.Field;
 import org.junit.rules.ExternalResource;
 
 /**
@@ -37,18 +39,42 @@ public NetworkTable getPreferencesTable() {
   protected void before() {
     prevInstance = Preferences.getNetworkTable().getInstance();
     tempInstance = NetworkTableInstance.create();
-    tempInstance.startLocal();
     Preferences.setNetworkTableInstance(tempInstance);
+    removePreferencesListener();
   }
 
   @Override
   protected void after() {
     Preferences.setNetworkTableInstance(prevInstance);
-    if (!tempInstance.waitForListenerQueue(.6)) {
+
+    // Clear out the listener queue before destroying our temporary NetworkTableInstance.
+    //
+    // This works around a race condition in WPILib where a listener registered by Preferences can
+    // be called after the NetworkTableInstance was closed (see
+    // https://github.com/wpilibsuite/allwpilib/issues/8215).
+    if (!tempInstance.waitForListenerQueue(4)) {
       System.err.println(
-          "Timed out waiting for the NetworkTableInstance listener queue to empty (waited 600ms);"
-              + " JVM may crash");
+          "Timed out waiting for the NetworkTableInstance listener queue to empty (waited 400ms);"
+              + " will not close temporary NetworkTableInstance");
+    } else {
+      tempInstance.close();
+    }
+  }
+
+  /**
+   * Removes the listener installed by {@link
+   * Preferences#setNetworkTableInstance(NetworkTableInstance)}.
+   *
+   * <p>The listener is a constant source of SIGSEGVs in our GitHub test actions.
+   */
+  private static void removePreferencesListener() {
+    try {
+      Field listnerField = Preferences.class.getDeclaredField("m_listener");
+      listnerField.setAccessible(true);
+      NetworkTableListener listener = (NetworkTableListener) listnerField.get(null);
+      listnerField.set(null, null);
+      listener.close();
+    } catch (NoSuchFieldException | IllegalAccessException e) {
     }
-    tempInstance.close();
   }
 }

testing/src/main/java/com/team2813/lib2813/testing/junit/jupiter/IsolatedNetworkTablesExtension.java

@@ -16,7 +16,9 @@
 package com.team2813.lib2813.testing.junit.jupiter;
 
 import edu.wpi.first.networktables.NetworkTableInstance;
+import edu.wpi.first.networktables.NetworkTableListener;
 import edu.wpi.first.wpilibj.Preferences;
+import java.lang.reflect.Field;
 import org.junit.jupiter.api.extension.AfterEachCallback;
 import org.junit.jupiter.api.extension.BeforeEachCallback;
 import org.junit.jupiter.api.extension.Extension;
@@ -56,6 +58,7 @@ public void beforeEach(ExtensionContext context) {
     NetworkTableInstance ntInstance =
         DATA_KEY.getOrComputeIfAbsent(store, Data::create).testInstance;
     Preferences.setNetworkTableInstance(ntInstance);
+    removePreferencesListener();
   }
 
   @Override
@@ -71,12 +74,13 @@ public void afterEach(ExtensionContext context) {
       // This works around a race condition in WPILib where a listener registered by Preferences can
       // be called after the NetworkTableInstance was closed (see
       // https://github.com/wpilibsuite/allwpilib/issues/8215).
-      if (!data.testInstance.waitForListenerQueue(.6)) {
+      if (!data.testInstance.waitForListenerQueue(.4)) {
         System.err.println(
-            "Timed out waiting for the NetworkTableInstance listener queue to empty (waited 600ms);"
-                + " JVM may crash");
+            "Timed out waiting for the NetworkTableInstance listener queue to empty (waited 400ms);"
+                + " will not close temporary NetworkTableInstance");
+      } else {
+        data.testInstance.close();
       }
-      data.testInstance.close();
     }
   }
 
@@ -101,9 +105,25 @@ public NetworkTableInstance resolveParameter(
   private record Data(NetworkTableInstance testInstance, NetworkTableInstance prevInstance) {
     static Data create() {
       NetworkTableInstance testInstance = NetworkTableInstance.create();
-      testInstance.startLocal();
       NetworkTableInstance prevInstance = Preferences.getNetworkTable().getInstance();
       return new Data(testInstance, prevInstance);
     }
   }
+
+  /**
+   * Removes the listener installed by {@link
+   * Preferences#setNetworkTableInstance(NetworkTableInstance)}.
+   *
+   * <p>The listener is a constant source of SIGSEGVs in our GitHub test actions.
+   */
+  private static void removePreferencesListener() {
+    try {
+      Field listnerField = Preferences.class.getDeclaredField("m_listener");
+      listnerField.setAccessible(true);
+      NetworkTableListener listener = (NetworkTableListener) listnerField.get(null);
+      listnerField.set(null, null);
+      listener.close();
+    } catch (NoSuchFieldException | IllegalAccessException e) {
+    }
+  }
 }