为移动应用集成 Rust + Flutter + Kotlin

Question

由于下周将有重要的 Rust 2018 和 Flutter 1.0 发布，我想构建一个使用 Rust 作为业务逻辑和 Flutter 作为用户界面的应用程序，它可以在 Android 和 iOS 上运行，我构建了一个并进行了测试它在 Android 上运行良好。

我只是想知道如何衡量性能并将其与原生 Android/iOS 应用程序进行比较。

应用流程是：

1. Main在Flutter中，即通过platform_channel调用native函数
2. native函数通过JNI调用rust库（调用rust库需要JNI封装）

结构如下：

使用的代码是：

main.dart:

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  static const platform = const MethodChannel('samples.flutter.io/battery');

  String _batteryLevel = 'Unknown battery level.';

  Future<void> _getBatteryLevel() async {
    String batteryLevel;
    try {
      final String hello = await platform.invokeMethod('getText');
      final int result = await platform.invokeMethod('getBatteryLevel');

      batteryLevel = '$hello Battery level at $result %.';
    } on PlatformException catch (e) {
      batteryLevel = "Failed to get battery level: '${e.message}'.";
    }

    setState(() {
      _batteryLevel = batteryLevel;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            RaisedButton(
              child: Text('Get Battery Level'),
              onPressed: _getBatteryLevel,
            ),
            Text(_batteryLevel),
          ],
        ),
      ),
    );
  }
}

JNI wrapper - RustGreetings.kt

package com.mozilla.greetings

class RustGreetings {
    companion object {
        init {
            System.loadLibrary("greetings")
        }
    }

    private external fun greeting(pattern: String): String

    fun sayHello(to: String): String = greeting(to)
}

主要的 Android 活动是：

package com.example.batterylevel

import android.os.Bundle
import io.flutter.app.FlutterActivity
import io.flutter.plugins.GeneratedPluginRegistrant
import io.flutter.plugin.common.MethodChannel

import android.content.Context
import android.content.ContextWrapper
import android.content.Intent
import android.content.IntentFilter
import android.os.BatteryManager
import android.os.Build.VERSION
import android.os.Build.VERSION_CODES

import lib.Library
import com.mozilla.greetings.RustGreetings

class MainActivity: FlutterActivity() {
  private val CHANNEL = "samples.flutter.io/battery"

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    GeneratedPluginRegistrant.registerWith(this)

    MethodChannel(flutterView, CHANNEL).setMethodCallHandler { call, result ->
      if (call.method == "getText") {
        result.success(getText())
      } else if (call.method == "getBatteryLevel") {
       // result.success(getText())
        val batteryLevel = getBatteryLevel()

        if (batteryLevel != -1) {
          result.success(batteryLevel)
        } else {
          result.error("UNAVAILABLE", "Battery level not available.", null)
        }
      }
      else {

        result.notImplemented()
      }
    }
  }

  private fun getBatteryLevel(): Int {
    val batteryLevel: Int
    if (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) {
      val batteryManager = getSystemService(Context.BATTERY_SERVICE) as BatteryManager
      batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
    } else {
      val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
      batteryLevel = intent!!.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
    }
    return batteryLevel
  }

  private fun getText(): String {
    val x = Library().someLibraryMethod()
    val g = RustGreetings()
    val r = g.sayHello("My $x Rust")
    return r
  }
}

在 Android gradle.build 中，我刚刚添加了以下内容，因为我有兴趣检查添加 kotlin JVM 库并使其与移动应用程序中的 Rust 库交互的影响：

dependencies {
    implementation(files("src/main/libs/lib.jar"))
}

我的问题是： 如何检查每个进程在被另一个进程执行或调用时的性能和影响

Answer 1

随着 Dart 中 ffi 的引入，现在事情变得更加顺畅，性能更好，因为现在直接与 Dart/Rust 交互，无需 Dart/Kotlin/Rust 或 Dart/Swift/Rust 循环，下面是一个简单的例子：

第一个src/lib.rs

#[no_mangle]
pub extern fn rust_fn(x: i32) -> i32 {   
    println!("Hello from rust\nI'll return: {}", x.pow(2));
    x.pow(2)
 }

和Cargo.toml

[package]
name = "Double_in_Rost"
version = "0.1.0"
authors = ["Hasan Yousef"]
edition = "2018"

[lib]
name = "rust_lib"
crate-type = ["dylib"] # could be `staticlib` as well

[dependencies]

运行cargo build --release 将生成target\release\rust_lib.dll 将其复制/粘贴到Dart 应用程序根目录中

如下编写 Dart 代码：

import 'dart:ffi';
import 'dart:io' show Platform;

// FFI signature of the hello_world C function
typedef ffi_func = Int32 Function(Int32 x);  //pub extern fn rust_fn(x: i32) -> i32
// Dart type definition for calling the C foreign function
typedef dart_func = int Function(int x);

void main() {
  // Open the dynamic library
  var path = './rust_lib.so';
  if (Platform.isMacOS) path = './rust_lib.dylib';
  if (Platform.isWindows) path = 'rust_lib.dll';
  final dylib = DynamicLibrary.open(path);
  // Look up the Rust/C function
  final my_func =
      dylib.lookup<NativeFunction<ffi_func>>('rust_fn').asFunction<dart_func>();
  print('Double of 3 is ${my_func(3)}');
}