flutter engine 那些沒被釋放的東西

因爲flutter一直存在內存泄漏的問題，致使不少開發者不勝困擾，博主在0.9.4就開始對其代碼內部內存問題在engine層面修改代碼，獲得解決，可是對於每一個版本都須要跟隨官方打包,對於開發者並非很友好。

然而喜出望外的是，在後來的幾個版本中，官方內置開發了手動釋放內存的方式😸

/**
 * 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;

複製代碼

翻譯以下：

銷燬引擎的運行上下文。 此方法可用於強制FlutterEngine對象釋放全部資源。 發送此消息後，對象將處於不可用狀態，直到解除分配爲止。 訪問屬性或向其發送消息將致使未定義的行爲或運行時錯誤。

可是,可是,可是，(重要的事說三遍) 在Flutter engine開發羣裏面，有羣友反饋還有不少問題

1. 沒法徹底釋放內存

2. 偶現崩潰

3. 官方回覆，慎用 github.com/flutter/flu…

偶現崩潰的是什麼鬼，暫時沒有遇到，很差說。 以前博主遇到的崩潰是本身使用方式的問題，在fluttervc關閉以後還有任務在執行methodchannel，即還在調用plugin，這個能夠在開發上避免。 值得注意的是，flutter中使用c++實現，本身對於內存管理並非很好

內存問題自測以下

確實存在問題，還有將近30M沒有被釋放，查看一下當前內存對象，以下圖

一個一個看還有那些沒有被釋放吧

android:LruCache

Least Recently Used 近期最少使用算法。 內存管理的一種頁面置換算法，對於在內存中但又不用的數據塊（內存塊）叫作LRU，flutter engine 會根據哪些數據屬於LRU而將其移出內存而騰出空間來加載另外的數據。

dart::BackgroundComplier 對isolate編譯優化的類

BackgroundCompiler 在後臺線程中運行優化編譯的類。 實現：每一個隔離一個任務，它與擁有isolate一塊兒消失，後臺編譯器中沒有OSR編譯。

dart::bin::socket

vm和開發平臺通訊的機制，好比jit即時編譯的dill文件，經過socket傳遞給dart vm，vm經過rpc加載文件，重置線程，從而實現hotreload熱重載

dart::BoolPrameter

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

定義在dart vm，service.cc中，都繼承自MethodParameter，作對應參數校驗，參數解析用。編譯dart文件用的

dart::OSThread

在dart 運行時負責操做系統線程，建立線程，移除線程，線程查找與管理。 以下圖

FlutterEngineRegistrar 註冊使用key註冊plugin的地方，全部plugin調用dart底層的方法都會經過 handlemethodcall 回調給使用者， 其初始化的地方是引發內存泄漏的地方

- (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;
}
複製代碼

此處有一篇文章介紹，解決engine的循環引用 文章

FlutterStandardMethodCodec 標準方法編解碼

FlutterStringCodec string編解碼 FlutterJsonMessageCodec json編解碼

不看不知道，一看嚇一跳，也居然是個單例，固然不會被釋放了，也能理解，在flutter中用到jsonmssage的地方不少，用不着每次都初始化

代碼實現的地方

@implementation FlutterJSONMessageCodec
+ (instancetype)sharedInstance {
  static id _sharedInstance = nil;
  if (!_sharedInstance) {
    _sharedInstance = [FlutterJSONMessageCodec new];
  }
  return _sharedInstance;
}
複製代碼

std:share_ptrxxx 共享指針

指針獲取 flutter isolate service dartvm symbolmapping

~~ 文章完 ~~

若是你想深刻討論flutter的問題，歡迎加入咱們的QQ羣 217429001

完整測試代碼以下

#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:@"加載boundle資源" 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{
 
}

/**

* 加載boundle資源

*/
- (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:@"關閉" 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

複製代碼

原創不易，版權全部，轉載請備註 code4flutter.com