Test TetheringManager could be GC after getting connector

There is pollingConnector thread which start polling connector if
TetheringManager is created earlier than TetheringService started(during
device boot up). TetheringManager won't be GCed if pollingConnector
thread do not finish its task yet.

Bug: 177265744
Bug: 191798390
Bug: 187972579
Test: atest TetheringServiceTest
Change-Id: Id8c7d10c5172e1d5de460c5311ff9c20261facef

Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringServiceTest.java

@@ -28,6 +28,7 @@ import static android.net.TetheringManager.TETHER_ERROR_NO_ERROR;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.eq;
@@ -46,6 +47,7 @@ import android.net.TetheringManager;
 import android.net.TetheringRequestParcel;
 import android.net.ip.IpServer;
 import android.os.Bundle;
+import android.os.ConditionVariable;
 import android.os.Handler;
 import android.os.IBinder;
 import android.os.ResultReceiver;
@@ -63,7 +65,6 @@ import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
-import org.mockito.Matchers;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
@@ -503,38 +504,81 @@ public final class TetheringServiceTest {
         });
     }
 
+    private class ConnectorSupplier<T> implements Supplier<T> {
+        private T mResult = null;
+
+        public void set(T result) {
+            mResult = result;
+        }
+
+        @Override
+        public T get() {
+            return mResult;
+        }
+    }
+
+    private void forceGc() {
+        System.gc();
+        System.runFinalization();
+        System.gc();
+    }
+
     @Test
     public void testTetheringManagerLeak() throws Exception {
         runAsAccessNetworkState((none) -> {
             final ArrayList<ITetheringEventCallback> callbacks = new ArrayList<>();
+            final ConditionVariable registeredCv = new ConditionVariable(false);
             doAnswer((invocation) -> {
                 final Object[] args = invocation.getArguments();
                 callbacks.add((ITetheringEventCallback) args[0]);
+                registeredCv.open();
                 return null;
-            }).when(mTethering).registerTetheringEventCallback(Matchers.anyObject());
+            }).when(mTethering).registerTetheringEventCallback(any());
 
-            final Supplier<IBinder> supplier = () -> mMockConnector.getIBinder();
+            doAnswer((invocation) -> {
+                final Object[] args = invocation.getArguments();
+                callbacks.remove((ITetheringEventCallback) args[0]);
+                return null;
+            }).when(mTethering).unregisterTetheringEventCallback(any());
+
+            final ConnectorSupplier<IBinder> supplier = new ConnectorSupplier<>();
 
             TetheringManager tm = new TetheringManager(mMockConnector.getService(), supplier);
             assertNotNull(tm);
-            assertEquals("Internal callback is not registered", 1, callbacks.size());
+            assertEquals("Internal callback should not be registered", 0, callbacks.size());
 
-            final WeakReference weakTm = new WeakReference(tm);
+            final WeakReference<TetheringManager> weakTm = new WeakReference(tm);
             assertNotNull(weakTm.get());
 
+            // TetheringManager couldn't be GCed because pollingConnector thread implicitly
+            // reference TetheringManager object.
             tm = null;
+            forceGc();
+            assertNotNull(weakTm.get());
+
+            // After getting connector, pollingConnector thread stops and internal callback is
+            // registered.
+            supplier.set(mMockConnector.getIBinder());
+            final long timeout = 500L;
+            if (!registeredCv.block(timeout)) {
+                fail("TetheringManager poll connector fail after " + timeout + " ms");
+            }
+            assertEquals("Internal callback is not registered", 1, callbacks.size());
+            assertNotNull(weakTm.get());
+
             final int attempts = 100;
             final long waitIntervalMs = 50;
             for (int i = 0; i < attempts; i++) {
-                System.gc();
-                System.runFinalization();
-                System.gc();
+                forceGc();
                 if (weakTm.get() == null) break;
 
                 Thread.sleep(waitIntervalMs);
             }
             assertNull("TetheringManager weak reference still not null after " + attempts
                     + " attempts", weakTm.get());
+
+            // BUG: internal callback do not be unregistered after TetheringManager is GCed.
+            assertEquals(1, callbacks.size());
         });
     }
 }