Suppress guest explicit GC with universal transform version

app/src/main/java/javax/microedition/lcdui/Canvas.java

@@ -200,7 +200,7 @@ public static void setSettings(ProfileModel settings) {
 		parallelRedraw = (mode == 0 || mode == 3) && settings.parallelRedrawScreen;
 	}
 
-	/** Enables the diagnostic only when the loaded artifact advertises the timing transform ABI. */
+	/** Enables the diagnostic only when the loaded artifact has the current universal transform. */
 	public static void setTimingOverlayEnabled(boolean enabled) {
 		timingOverlayEnabled = enabled;
 	}

app/src/main/java/javax/microedition/shell/GuestTimingBridge.java

@@ -33,8 +33,6 @@
  * provide or shadow this class.
  */
 public final class GuestTimingBridge {
-	public static final int ABI_VERSION = 4;
-
 	private static final Object LOCK = new Object();
 	private static TimingSession activeSession;
 

app/src/main/java/javax/microedition/shell/MicroLoader.java

@@ -82,7 +82,7 @@
 import javax.microedition.shell.timing.EmulationSpeed;
 import javax.microedition.shell.timing.TimingSession;
 import javax.microedition.shell.timing.TimingMode;
-import javax.microedition.shell.timing.TimingTransformMetadata;
+import javax.microedition.shell.transform.MidletTransformMetadata;
 
 public class MicroLoader {
 	private static final String TAG = MicroLoader.class.getName();
@@ -200,9 +200,9 @@ private boolean hasCompatibleTimingTransform() {
 		try {
 			Descriptor descriptor = new Descriptor(
 					new File(appDir, Config.MIDLET_MANIFEST_FILE), false);
-			return TimingTransformMetadata.isCompatible(descriptor.getAttrs());
+			return MidletTransformMetadata.isCompatible(descriptor.getAttrs());
 		} catch (IOException | RuntimeException e) {
-			Log.w(TAG, "Timing transform metadata is unavailable", e);
+			Log.w(TAG, "MIDlet transform metadata is unavailable", e);
 			return false;
 		}
 	}

app/src/main/java/javax/microedition/shell/MidletSystem.java

@@ -35,4 +35,19 @@ public static String getProperty(String key, String def) {
         return value;
     }
 
+    /**
+     * Handles an advisory garbage-collection request made by a MIDlet.
+     *
+     * <p>Forwarding every guest request to Android can start a compacting collection inside hot
+     * MIDlet loops. ART still collects normally when allocation pressure requires it.</p>
+     */
+    public static void gc() {
+        // Java ME only requires the VM to make a best effort, so the emulator may ignore the hint.
+    }
+
+    /** Preserves the receiver null check while suppressing {@link Runtime#gc()} from guest code. */
+    public static void gc(Runtime runtime) {
+        if (runtime == null) throw new NullPointerException("runtime");
+    }
+
 }

app/src/main/java/javax/microedition/shell/transform/MidletTransformMetadata.java

@@ -0,0 +1,51 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package javax.microedition.shell.transform;
+
+import java.util.Map;
+
+/**
+ * Universal compatibility marker for an installed MIDlet's transformed bytecode.
+ *
+ * <p>Increment {@link #TRANSFORM_VERSION} whenever the converter changes emitted bytecode or a
+ * runtime bridge contract used by that bytecode. Installed MIDlets with an older or missing marker
+ * are then rebuilt by the normal app reconversion path when their retained source is available.</p>
+ */
+public final class MidletTransformMetadata {
+	/** Version 1 includes guest-time virtualization and suppression of advisory explicit GC. */
+	public static final int TRANSFORM_VERSION = 1;
+	public static final String TRANSFORM_VERSION_ATTRIBUTE = "JLMod-Transform-Version";
+	private static final String LEGACY_TIMING_TRANSFORM_ATTRIBUTE =
+			"JLMod-Timing-Transform-Version";
+	private static final String LEGACY_TIMING_BRIDGE_ATTRIBUTE = "JLMod-Timing-Bridge-ABI";
+
+	private MidletTransformMetadata() {
+	}
+
+	public static void mark(Map<String, String> attributes) {
+		if (attributes == null) {
+			throw new NullPointerException("attributes");
+		}
+		attributes.remove(LEGACY_TIMING_TRANSFORM_ATTRIBUTE);
+		attributes.remove(LEGACY_TIMING_BRIDGE_ATTRIBUTE);
+		attributes.put(TRANSFORM_VERSION_ATTRIBUTE, Integer.toString(TRANSFORM_VERSION));
+	}
+
+	public static boolean isCompatible(Map<String, String> attributes) {
+		return attributes != null
+				&& Integer.toString(TRANSFORM_VERSION).equals(
+						attributes.get(TRANSFORM_VERSION_ATTRIBUTE));
+	}
+}

app/src/main/java/ru/playsoftware/j2meloader/config/ConfigActivity.java

@@ -53,7 +53,7 @@
 import java.util.List;
 import java.util.Set;
 
-import javax.microedition.shell.timing.TimingTransformMetadata;
+import javax.microedition.shell.transform.MidletTransformMetadata;
 import javax.microedition.util.ContextHolder;
 
 import kotlin.io.FilesKt;
@@ -996,7 +996,7 @@ private boolean hasCompatibleTimingTransform() {
 		try {
 			Descriptor descriptor = new Descriptor(
 					new File(appDir, Config.MIDLET_MANIFEST_FILE), false);
-			return TimingTransformMetadata.isCompatible(descriptor.getAttrs());
+			return MidletTransformMetadata.isCompatible(descriptor.getAttrs());
 		} catch (IOException | RuntimeException e) {
 			return false;
 		}

app/src/main/java/ru/woesss/j2me/installer/AppInstaller.java

@@ -62,7 +62,7 @@
 import ru.woesss.j2me.jar.Descriptor;
 import ru.woesss.util.TextUtils;
 import ru.woesss.util.zip.ZipFile;
-import javax.microedition.shell.timing.TimingTransformMetadata;
+import javax.microedition.shell.transform.MidletTransformMetadata;
 
 public class AppInstaller {
     private static final String TAG = AppInstaller.class.getSimpleName();
@@ -431,7 +431,7 @@ void install(SingleEmitter<Integer> emitter) throws ConverterException, IOExcept
                 manifest.merge(newDesc);
                 newDesc = manifest;
             }
-            TimingTransformMetadata.mark(newDesc.getAttrs());
+            MidletTransformMetadata.mark(newDesc.getAttrs());
 
             File resJar = child(tmpDir, Config.MIDLET_RES_FILE);
             FileUtils.copyFileUsingChannel(srcJar, resJar);

app/src/main/java/ru/woesss/j2me/installer/AppReconverter.java

@@ -27,7 +27,7 @@
 import java.io.IOException;
 import java.util.jar.JarFile;
 
-import javax.microedition.shell.timing.TimingTransformMetadata;
+import javax.microedition.shell.transform.MidletTransformMetadata;
 
 import ru.playsoftware.j2meloader.config.Config;
 import ru.playsoftware.j2meloader.librarydb.LibraryIconOverride;
@@ -61,9 +61,9 @@ public static boolean needsReconversion(File appDir) {
         if (payload == null || !Config.isUsableFile(descriptorFile)) return true;
         try {
             Descriptor descriptor = new Descriptor(descriptorFile, false);
-            return !TimingTransformMetadata.isCompatible(descriptor.getAttrs());
+            return !MidletTransformMetadata.isCompatible(descriptor.getAttrs());
         } catch (IOException | RuntimeException error) {
-            Log.w(TAG, "Unable to validate converted timing marker: " + appDir, error);
+            Log.w(TAG, "Unable to validate converted transform marker: " + appDir, error);
             return true;
         }
     }
@@ -129,7 +129,7 @@ public static void reconvert(File requestedAppDir) throws IOException, Converter
                 if (!generatedPayload.isFile() || generatedPayload.length() <= 0L) {
                     throw new ConverterException("DX produced no converted MIDlet payload");
                 }
-                TimingTransformMetadata.mark(descriptor.getAttrs());
+                MidletTransformMetadata.mark(descriptor.getAttrs());
                 FileUtils.copyFileUsingChannel(retainedJar, fileWithSuffix(staging, Config.MIDLET_RES_FILE));
                 extractIcon(descriptor, retainedJar, staging);
                 descriptor.writeTo(fileWithSuffix(staging, Config.MIDLET_MANIFEST_FILE));

app/src/test/java/javax/microedition/shell/MidletSystemTest.java

@@ -0,0 +1,30 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package javax.microedition.shell;
+
+import org.junit.Test;
+
+public class MidletSystemTest {
+	@Test
+	public void advisoryGcRequestsReturnWithoutCollecting() {
+		MidletSystem.gc();
+		MidletSystem.gc(Runtime.getRuntime());
+	}
+
+	@Test(expected = NullPointerException.class)
+	public void runtimeGcBridgePreservesReceiverNullCheck() {
+		MidletSystem.gc((Runtime) null);
+	}
+}

app/src/test/java/javax/microedition/shell/transform/MidletTransformMetadataTest.java

@@ -0,0 +1,60 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package javax.microedition.shell.transform;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class MidletTransformMetadataTest {
+	@Test
+	public void currentVersionIsCompatibleAfterMarking() {
+		Map<String, String> attributes = new HashMap<>();
+		MidletTransformMetadata.mark(attributes);
+
+		assertTrue(MidletTransformMetadata.isCompatible(attributes));
+	}
+
+	@Test
+	public void missingOrChangedUniversalVersionIsRejected() {
+		Map<String, String> attributes = new HashMap<>();
+		MidletTransformMetadata.mark(attributes);
+		attributes.put(MidletTransformMetadata.TRANSFORM_VERSION_ATTRIBUTE, "999");
+
+		assertFalse(MidletTransformMetadata.isCompatible(attributes));
+		assertFalse(MidletTransformMetadata.isCompatible(new HashMap<>()));
+		assertFalse(MidletTransformMetadata.isCompatible(null));
+	}
+
+	@Test
+	public void legacyTimingOnlyMarkerTriggersUniversalReconversion() {
+		Map<String, String> attributes = new HashMap<>();
+		attributes.put("JLMod-Timing-Transform-Version", "6");
+		attributes.put("JLMod-Timing-Bridge-ABI", "4");
+
+		assertFalse(MidletTransformMetadata.isCompatible(attributes));
+
+		MidletTransformMetadata.mark(attributes);
+
+		assertTrue(MidletTransformMetadata.isCompatible(attributes));
+		assertNull(attributes.get("JLMod-Timing-Transform-Version"));
+		assertNull(attributes.get("JLMod-Timing-Bridge-ABI"));
+	}
+}