AndroidRuntime: Expose GetJavaVM

Add a new header library, libandroid_runtime_vm_headers,
that exposes AndroidRuntimeGetJavaVM.

Test: boots
Bug: 190450693
Change-Id: I64053b56eb1290cff8ea191b1cc592fbc9702ce8

core/jni/Android.bp

@@ -297,6 +297,7 @@ cc_library_shared {
             header_libs: [
                 "bionic_libc_platform_headers",
                 "dnsproxyd_protocol_headers",
+                "libandroid_runtime_vm_headers",
             ],
         },
         host: {
@@ -338,3 +339,29 @@ cc_library_shared {
         never: true,
     },
 }
+
+cc_library_headers {
+    name: "libandroid_runtime_vm_headers",
+    host_supported: true,
+    vendor_available: true,
+    // TODO(b/153609531): remove when libbinder is not native_bridge_supported
+    native_bridge_supported: true,
+    // Allow only modules from the following list to create threads that can be
+    // attached to the JVM. This list should be a subset of the dependencies of
+    // libandroid_runtime.
+    visibility: [
+        "//frameworks/native/libs/binder",
+    ],
+    export_include_dirs: ["include_vm"],
+    header_libs: [
+        "jni_headers",
+    ],
+    export_header_lib_headers: [
+        "jni_headers",
+    ],
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.media",
+        "com.android.media.swcodec",
+    ],
+}

core/jni/AndroidRuntime.cpp

@@ -22,6 +22,7 @@
 #include <android-base/properties.h>
 #include <android/graphics/jni_runtime.h>
 #include <android_runtime/AndroidRuntime.h>
+#include <android_runtime/vm.h>
 #include <assert.h>
 #include <binder/IBinder.h>
 #include <binder/IPCThreadState.h>
@@ -1322,6 +1323,10 @@ void AndroidRuntime::onVmCreated(JNIEnv* env)
     return AndroidRuntime::mJavaVM;
 }
 
+extern "C" JavaVM* AndroidRuntimeGetJavaVM() {
+    return AndroidRuntime::getJavaVM();
+}
+
 /*
  * Get the JNIEnv pointer for this thread.
  *

core/jni/include_vm/android_runtime/vm.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <jni.h>
+
+// Get the Java VM. If the symbol doesn't exist at runtime, it means libandroid_runtime
+// is not loaded in the current process. If the symbol exists but it returns nullptr, it
+// means JavaVM is not yet started.
+extern "C" JavaVM* AndroidRuntimeGetJavaVM();