JNI: Fix reference leak in QJniArray

When the array type is QJniObject or a subclass, then we need to
explicitly release the local reference returned by GetObjectArrayElement
in the QJniArray::at implementation. Do this by constructing the
QJniObject via fromLocalRef, which does exactly that.
Amends 80d4d55e250af1d643805bde3821987112cf09c1.

Add a test case that stresses the local reference pool, and fix the old
test case (which operates on a QJniArray<jobject>) to also release the
local references.

Change-Id: Ie293b1db9f1b6825376bbf12338b22dfc3f8c6e9
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

1 files changed, 24 insertions, 3 deletions

diff --git a/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp b/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
index c39a6d0343..c658c35bb0 100644
--- a/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
+++ b/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
@@ -113,6 +113,7 @@ private slots:
     void templateApiCheck();
     void isClassAvailable();
     void fromLocalRef();
+    void largeObjectArray();
 
     void callback_data();
     void callback();
@@ -1534,9 +1535,10 @@ void tst_QJniObject::templateApiCheck()
         const auto reverse = testClass.callMethod<jobject[]>("reverseObjectArray", newArray);
         QVERIFY(reverse.isValid());
         QCOMPARE(reverse.size(), 3);
-        QCOMPARE(QJniObject(reverse.at(0)).toString(), u"three"_s);
-        QCOMPARE(QJniObject(reverse.at(1)).toString(), u"two"_s);
-        QCOMPARE(QJniObject(reverse.at(2)).toString(), u"one"_s);
+        // QJniArray::at returns a jobject that's a local reference; make sure we don't free it twice
+        QCOMPARE(QJniObject::fromLocalRef(reverse.at(0)).toString(), u"three"_s);
+        QCOMPARE(QJniObject::fromLocalRef(reverse.at(1)).toString(), u"two"_s);
+        QCOMPARE(QJniObject::fromLocalRef(reverse.at(2)).toString(), u"one"_s);
     }
 
     // jbooleanArray ------------------------------------------------------------------------------
@@ -1842,6 +1844,25 @@ void tst_QJniObject::fromLocalRef()
         QJniObject o = QJniObject::fromLocalRef(env->FindClass("java/lang/String"));
 }
 
+void tst_QJniObject::largeObjectArray()
+{
+    QJniArray<jobject> newArray(QList<QJniObject>{QJniObject::fromString(u"one"_s),
+                                                    QJniObject::fromString(u"two"_s),
+                                                    QJniObject::fromString(u"three"_s)});
+    QVERIFY(newArray.isValid());
+    const QJniArray<QJniObject> reverse = TestClass::callStaticMethod<jobject[]>(
+                                                            "staticReverseObjectArray", newArray);
+    QVERIFY(reverse.isValid());
+    QCOMPARE(reverse.size(), 3);
+
+    // make sure we don't leak local references
+    for (int i = 0; i < 10000; ++i) {
+        QVERIFY(reverse.at(0).isValid());
+        QVERIFY(reverse.at(1).isValid());
+        QVERIFY(reverse.at(2).isValid());
+    }
+}
+
 
 static std::optional<TestClass> calledWithObject;
 static int callbackWithObject(JNIEnv *, jobject, TestClass that)