JavaKit: support for Android NDK JVM

Author: lhoward

Package.swift

@@ -202,7 +202,9 @@ let package = Package(
             "-L\(javaHome)/lib"
           ],
           .when(platforms: [.windows])),
-        .linkedLibrary("jvm"),
+        .linkedLibrary(
+          "jvm",
+          .when(platforms: [.iOS, .macOS, .tvOS, .watchOS, .macCatalyst, .linux, .openbsd, .wasi, .windows])),
       ]
     ),
     .target(

Samples/JavaKitSampleApp/Package.swift

@@ -30,7 +30,7 @@ func findJavaHome() -> String {
 }
 let javaHome = findJavaHome()
 
-let javaIncludePath = "\(javaHome)/include"
+let javaIncludePath = ProcessInfo.processInfo.environment["JAVA_INCLUDE_PATH"] ?? "\(javaHome)/include"
 #if os(Linux)
   let javaPlatformIncludePath = "\(javaIncludePath)/linux"
 #elseif os(macOS)

Samples/JavaKitSampleApp/Sources/JavaKitExample/JavaKitExample.swift

@@ -27,7 +27,10 @@ extension HelloSwift: HelloSwiftNativeMethods {
     let answer = self.sayHelloBack(i + j)
     print("Swift got back \(answer) from Java")
 
+#if !canImport(Android)
+    // no class variables in Kotlin
     print("We expect the above value to be the initial value, \(self.javaClass.initialValue)")
+#endif
 
     print("Updating Java field value to something different")
     self.value = 2.71828

Sources/ExampleSwiftLibrary/MySwiftLibrary.swift

@@ -23,6 +23,8 @@ import Glibc
 import CRT
 #elseif canImport(Darwin)
 import Darwin.C
+#elseif canImport(Android)
+import Android
 #endif
 
 public func helloWorld() {

Sources/JavaKit/JavaEnvironment.swift

@@ -14,6 +14,10 @@
 
 import JavaRuntime
 
+#if canImport(Android)
+typealias JNINativeInterface_ = JNINativeInterface
+#endif
+
 extension UnsafeMutablePointer<JNIEnv?> {
   var interface: JNINativeInterface_ { self.pointee!.pointee }
 }

Sources/JavaKit/JavaKitVM/JavaVirtualMachine.swift

@@ -19,6 +19,11 @@ import Foundation
 #endif
 
 public typealias JavaVMPointer = UnsafeMutablePointer<JavaVM?>
+#if canImport(Android)
+typealias JNIEnvPointer = UnsafeMutablePointer<JNIEnv?>
+#else
+typealias JNIEnvPointer = UnsafeMutableRawPointer
+#endif
 
 public final class JavaVirtualMachine: @unchecked Sendable {
   /// The JNI version that we depend on.
@@ -61,7 +66,7 @@ public final class JavaVirtualMachine: @unchecked Sendable {
   ) throws {
     self.classpath = classpath
     var jvm: JavaVMPointer? = nil
-    var environment: UnsafeMutableRawPointer? = nil
+    var environment: JNIEnvPointer? = nil
     var vmArgs = JavaVMInitArgs()
     vmArgs.version = JavaVirtualMachine.jniVersion
     vmArgs.ignoreUnrecognized = jboolean(ignoreUnrecognized ? JNI_TRUE : JNI_FALSE)
@@ -161,12 +166,18 @@ extension JavaVirtualMachine {
       return environment.assumingMemoryBound(to: JNIEnv?.self)
     }
 
+#if canImport(Android)
+    var jniEnv = environment?.assumingMemoryBound(to: JNIEnv?.self)
+#else
+    var jniEnv = environment
+#endif
+
     // Attach the current thread to the JVM.
     let attachResult: jint
     if asDaemon {
-      attachResult = jvm.pointee!.pointee.AttachCurrentThreadAsDaemon(jvm, &environment, nil)
+      attachResult = jvm.pointee!.pointee.AttachCurrentThreadAsDaemon(jvm, &jniEnv, nil)
     } else {
-      attachResult = jvm.pointee!.pointee.AttachCurrentThread(jvm, &environment, nil)
+      attachResult = jvm.pointee!.pointee.AttachCurrentThread(jvm, &jniEnv, nil)
     }
 
     // If we failed to attach, report that.
@@ -175,9 +186,13 @@ extension JavaVirtualMachine {
       throw attachError
     }
 
-    JavaVirtualMachine.destroyTLS.set(environment!)
+    JavaVirtualMachine.destroyTLS.set(jniEnv!)
 
-    return environment!.assumingMemoryBound(to: JNIEnv?.self)
+#if canImport(Android)
+    return jniEnv!
+#else
+    return jniEnv!.assumingMemoryBound(to: JNIEnv?.self)
+#endif
   }
 
   /// Detach the current thread from the Java Virtual Machine. All Java

Sources/JavaRuntime/AndroidSupport.cpp

@@ -0,0 +1,98 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef __ANDROID__
+
+#include <JavaRuntime.h>
+#include <android/log.h>
+#include <dlfcn.h>
+
+// these are not exported by the Android SDK
+
+extern "C" {
+  using JavaRuntime_GetDefaultJavaVMInitArgs_fn = jint (*)(void *vm_args);
+  using JavaRuntime_CreateJavaVM_fn = jint (*)(JavaVM **, JNIEnv **, void *);
+  using JavaRuntime_GetCreatedJavaVMs_fn = jint (*)(JavaVM **, jsize, jsize *);
+}
+
+static JavaRuntime_GetDefaultJavaVMInitArgs_fn
+    JavaRuntime_GetDefaultJavaVMInitArgs;
+static JavaRuntime_CreateJavaVM_fn JavaRuntime_CreateJavaVM;
+static JavaRuntime_GetCreatedJavaVMs_fn JavaRuntime_GetCreatedJavaVMs;
+
+static void *JavaRuntime_dlhandle;
+
+__attribute__((constructor)) static void JavaRuntime_init(void) {
+  JavaRuntime_dlhandle = dlopen("libnativehelper.so", RTLD_NOW | RTLD_LOCAL);
+  if (JavaRuntime_dlhandle == nullptr) {
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "failed to open libnativehelper.so: %s", dlerror());
+    return;
+  }
+
+  JavaRuntime_GetDefaultJavaVMInitArgs =
+      reinterpret_cast<JavaRuntime_GetDefaultJavaVMInitArgs_fn>(
+          dlsym(JavaRuntime_dlhandle, "JNI_GetDefaultJavaVMInitArgs"));
+  if (JavaRuntime_GetDefaultJavaVMInitArgs == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_GetDefaultJavaVMInitArgs not found: %s",
+                        dlerror());
+
+  JavaRuntime_CreateJavaVM = reinterpret_cast<JavaRuntime_CreateJavaVM_fn>(
+      dlsym(JavaRuntime_dlhandle, "JNI_CreateJavaVM"));
+  if (JavaRuntime_CreateJavaVM == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_CreateJavaVM not found: %s", dlerror());
+
+  JavaRuntime_GetCreatedJavaVMs =
+      reinterpret_cast<JavaRuntime_GetCreatedJavaVMs_fn>(
+          dlsym(JavaRuntime_dlhandle, "JNI_GetCreatedJavaVMs"));
+  if (JavaRuntime_GetCreatedJavaVMs == nullptr)
+    __android_log_print(ANDROID_LOG_FATAL, "JavaRuntime",
+                        "JNI_GetCreatedJavaVMs not found: %s", dlerror());
+}
+
+__attribute__((destructor)) static void JavaRuntime_deinit(void) {
+  if (JavaRuntime_dlhandle) {
+    dlclose(JavaRuntime_dlhandle);
+    JavaRuntime_dlhandle = nullptr;
+  }
+
+  JavaRuntime_GetDefaultJavaVMInitArgs = nullptr;
+  JavaRuntime_CreateJavaVM = nullptr;
+  JavaRuntime_GetCreatedJavaVMs = nullptr;
+}
+
+jint JNI_GetDefaultJavaVMInitArgs(void *vm_args) {
+  if (JavaRuntime_GetDefaultJavaVMInitArgs == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_GetDefaultJavaVMInitArgs)(vm_args);
+}
+
+jint JNI_CreateJavaVM(JavaVM **vm, JNIEnv **env, void *vm_args) {
+  if (JavaRuntime_CreateJavaVM == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_CreateJavaVM)(vm, env, vm_args);
+}
+
+jint JNI_GetCreatedJavaVMs(JavaVM **vmBuf, jsize bufLen, jsize *nVMs) {
+  if (JavaRuntime_GetCreatedJavaVMs == nullptr)
+    return JNI_ERR;
+
+  return (*JavaRuntime_GetCreatedJavaVMs)(vmBuf, bufLen, nVMs);
+}
+
+#endif