flutter engine 那些没被释放的东西

时间 2019-11-06

原文原文链接

因为flutter一直存在内存泄漏的问题，致使不少开发者不胜困扰，博主在0.9.4就开始对其代码内部内存问题在engine层面修改代码，获得解决，可是对于每一个版本都须要跟随官方打包,对于开发者并非很友好。android

然而喜出望外的是，在后来的几个版本中，官方内置开发了手动释放内存的方式😸ios

/**
 * Destroy running context for an engine.
 *
 * This method can be used to force the FlutterEngine object to release all resources.
 * After sending this message, the object will be in an unusable state until it is deallocated.
 * Accessing properties or sending messages to it will result in undefined behavior or runtime
 * errors.
 */
- (void)destroyContext;

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翻译以下：c++

销毁引擎的运行上下文。此方法可用于强制FlutterEngine对象释放全部资源。发送此消息后，对象将处于不可用状态，直到解除分配为止。访问属性或向其发送消息将致使未定义的行为或运行时错误。git

可是,可是,可是，(重要的事说三遍) 在Flutter engine开发群里面，有群友反馈还有不少问题github

没法彻底释放内存算法

偶现崩溃json

官方回复，慎用 github.com/flutter/flu…bash

偶现崩溃的是什么鬼，暂时没有遇到，很差说。以前博主遇到的崩溃是本身使用方式的问题，在fluttervc关闭以后还有任务在执行methodchannel，即还在调用plugin，这个能够在开发上避免。值得注意的是，flutter中使用c++实现，本身对于内存管理并非很好app

内存问题自测以下dom

确实存在问题，还有将近30M没有被释放，查看一下当前内存对象，以下图

一个一个看还有那些没有被释放吧

android:LruCache

Least Recently Used 近期最少使用算法。内存管理的一种页面置换算法，对于在内存中但又不用的数据块（内存块）叫作LRU，flutter engine 会根据哪些数据属于LRU而将其移出内存而腾出空间来加载另外的数据。

dart::BackgroundComplier 对isolate编译优化的类

BackgroundCompiler 在后台线程中运行优化编译的类。实现：每一个隔离一个任务，它与拥有isolate一块儿消失，后台编译器中没有OSR编译。

dart::bin::socket

vm和开发平台通讯的机制，好比jit即时编译的dill文件，经过socket传递给dart vm，vm经过rpc加载文件，重置线程，从而实现hotreload热重载

dart::BoolPrameter

dart::EnumParameter
dart::IdParameter
dart::IdParameter
dart::xxxPrameter

定义在dart vm，service.cc中，都继承自MethodParameter，作对应参数校验，参数解析用。编译dart文件用的

dart::OSThread

在dart 运行时负责操做系统线程，建立线程，移除线程，线程查找与管理。以下图

FlutterEngineRegistrar 注册使用key注册plugin的地方，全部plugin调用dart底层的方法都会经过 handlemethodcall 回调给使用者，其初始化的地方是引发内存泄漏的地方

- (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine*)flutterEngine {
  self = [super init];
  NSAssert(self, @"Super init cannot be nil");
  _pluginKey = pluginKey;// [pluginKey retain];
  _flutterEngine = flutterEngine;// [flutterEngine retain];
  return self;
}
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此处有一篇文章介绍，解决engine的循环引用文章

FlutterStandardMethodCodec 标准方法编解码

FlutterStringCodec string编解码 FlutterJsonMessageCodec json编解码

不看不知道，一看吓一跳，也居然是个单例，固然不会被释放了，也能理解，在flutter中用到jsonmssage的地方不少，用不着每次都初始化

代码实现的地方

@implementation FlutterJSONMessageCodec
+ (instancetype)sharedInstance {
  static id _sharedInstance = nil;
  if (!_sharedInstance) {
    _sharedInstance = [FlutterJSONMessageCodec new];
  }
  return _sharedInstance;
}
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std:share_ptrxxx 共享指针

指针获取 flutter isolate service dartvm symbolmapping

~~ 文章完 ~~

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完整测试代码以下

#import "FlutterTesterViewController.h"
#import <Flutter/Flutter.h>
#import "GeneratedPluginRegistrant.h" 
 
@interface FlutterTesterViewController ()
@property (nonatomic, weak) FlutterViewController * ctr;
@property (nonatomic, weak) FlutterEngine * engine;
@end

@implementation FlutterTesterViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    
    float Y = 210;
    [self createButton:@"加载boundle资源" frame:CGRectMake(80.0, Y, 160.0, 40.0) action:@selector(handleBoundleResource )];
  
    Y += 40.0 + 10;
    [self createButton:@"autorelease" frame:CGRectMake(80.0, Y, 160.0, 40.0) action:@selector(handleAutoRelase)];
    
    NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString * path = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"flutter_assets"] ;
    NSLog(@"path: %@",path);
    
}

-(void)handleNetWorkResource:(UIButton *)button{
 
}

/**

* 加载boundle资源

*/
- (void)handleBoundleResource {
    
    FlutterDartProject * dart = [[FlutterDartProject alloc] init];
    FlutterEngine * engine = [[FlutterEngine alloc] initWithName:@"ios.dart.flutter"
                                                         project:dart];
    [engine runWithEntrypoint:nil];
    FlutterViewController* flutterViewController = [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
    [GeneratedPluginRegistrant registerWithRegistry:flutterViewController];
    [self addBackButton:flutterViewController];
     [flutterViewController setInitialRoute:@"route1"];
    [self presentViewController:flutterViewController animated:YES completion:nil];
    self.engine = engine;
}

-(void)handleAutoRelase{
 
     FlutterBasicMessageChannel* channel;
    FlutterEngine * engine;
    @autoreleasepool {
        FlutterViewController* flutterViewController =
        [[FlutterViewController alloc] init];
        channel = flutterViewController.engine.systemChannel;
        engine = flutterViewController.engine;
        NSLog(@"engine111:%@",engine);
    }
    NSLog(@"engine222:%@",engine);
    [channel sendMessage:@"Hello!"];
    [channel setMessageHandler:^(id  _Nullable message, FlutterReply  _Nonnull callback) { }];
}

-(void)addBackButton:(UIViewController *)flutterViewController{
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2  * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        UIButton * btn = [UIButton buttonWithType:UIButtonTypeSystem];
        [btn setTitle:@"关闭" forState:UIControlStateNormal];
        btn.frame = CGRectMake(10, 100, 50, 30);
        [btn addTarget:self action:@selector(buttonTap:) forControlEvents:UIControlEventTouchUpInside];
        [flutterViewController.view addSubview:btn];
        self.ctr = flutterViewController;
    });
}

-(void)buttonTap:(id)sender{
//    [self.navigationController popViewControllerAnimated:YES];
    
    __weak __typeof(self)weakSelf = self;
    [self.ctr dismissViewControllerAnimated:YES completion:^{
        
        [weakSelf.engine destroyContext];
    }];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}



-(UIButton *)createButton:(NSString *)title frame:(CGRect)frame action:(SEL)selector{
 
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    [button addTarget:self
               action:selector
     forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:title forState:UIControlStateNormal];
    UIColor * bgcolor = [UIColor colorWithRed:arc4random()%256/255. green:arc4random()%256/255. blue:arc4random()%256/255. alpha:1];
    [button setBackgroundColor:bgcolor];
    button.frame = frame;
    [self.view addSubview:button];
    return button;
}

@end

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