VM: CG raster data 崩溃探究

文长不看

1. 分析内存虚拟内存和堆内存（All Heap Allocagtions）都需要关注， VM 也是有区别的，有些会导致 OOM
2. VM: CG raster data 会导致崩溃
3. 创建22小位图，Instruments 标记的是堆内存，100100 的位图，Instruments 标记的是 VM: CG raster data
4. AutoLayout 用多了也要占用内存，CollectionCell 上最好都使用手动布局（不光内存更优，性能也更好）
5. 屏幕中 Cell 数量越多，占用内存越多。
6. Cell 越复杂，占用的内存越多

背景

有人反馈了打开一个面板内存上涨了 150m。instruments 分析以后得到如下数据：

150 M 其中大头都是 VM 内存， 勾选只看堆内存（All Heap Allocagtions） 创建的内存为 46M

30.88 MB 66.3% 262648 start

8.96 MB 19.2% 2845 thread_start

6.73 MB 14.4% 55930 start_wqthread

VM 内存会把机器搞挂么？

Case 1

我写了个 demo, 设置 kCGImageSourceShouldCacheImmediately = YES， kCGImageSourceShouldCache = YES。

在 iPad pro 上暴力测试，VM 上涨到 70 G （有点心疼我自己的机器，没有继续测试了），进程也一直没有挂。

Case 2

但是如果不断调用 UIGraphicsBeginImageContextWithOptions 创建位图并且不释放， CG raster data vm bu

Case 3

malloc 分配 堆内存 2.8G 时 OOM

这里我们得出结论：分析内存虚拟内存和堆内存（All Heap Allocagtions）都需要关注， VM部分也是有区别的，有些会导致 OOM，有些不会

Case 4

创建2*2小位图，Instruments 标记的是堆内存

- (void)testCGRasterDataOOM {
    // 小图用的是堆内存
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(2, 2), NO, 1);
    NSMutableArray *arr = [NSMutableArray new];
    while (1) {
        [arr addObject:UIGraphicsGetImageFromCurrentImageContext()];
    }
}

Case 5

创建 100*100 的位图，Instruments 标记的是 VM: CG raster data

- (void)viewDidLoad {
    [super viewDidLoad];
    _imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:_imageView];
    
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(4000, 4000), NO, 1);
    [[UIColor redColor] setFill];
    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, 4000, 4000));
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSData *data = UIImageJPEGRepresentation(img, 0.9);
    
    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
    [data writeToFile:cachePath atomically:YES];
  
    while (1) {
        @autoreleasepool {
						[self.class loadCachedImageWithoutDecode];
        }
    }
}

+ (nullable UIImage *)loadCachedImageWithoutDecode {
    
    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:cachePath]) {
        
        NSURL *imageUrl = [NSURL fileURLWithPath:cachePath];
        NSDictionary *imageSourceOptions = @{(__bridge id)kCGImageSourceShouldCache : @NO ,
                                             (__bridge id)kCGImageSourceShouldCacheImmediately : @NO};
        CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)imageUrl, (__bridge CFDictionaryRef)imageSourceOptions);
        if (imageSource) {
            NSDictionary *options = @{ (__bridge id)kCGImageSourceShouldCache : @YES ,
                                       (__bridge id)kCGImageSourceTypeIdentifierHint : (id)kUTTypeJPEG,
                                       (__bridge id)kCGImageSourceShouldCacheImmediately : @YES};
            CGImageRef imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, (__bridge CFDictionaryRef)options);
            CFRelease(imageSource);
            
            if (imageRef) {
                return [UIImage imageWithCGImage:imageRef];
            }
        }
    }
    return nil;
}

AutoLayout 也会是吃内存

一个奇怪的问题：AutoLayout 也会是吃内存的，特别是约束特别多的时候（贴纸面板的这个场景一口气加载了十几页的数据，创建了非常多的 Cell。

删除了约束改成手写 frame ，删除无用的控件以后，内存下降了14 M。

优化 6.73M 解码后的图片

图片缓存的问题：只在必要的时候解码，贴纸的场景，在绘制完本地的贴纸（因为有时间、用户名信息，需要经常重绘，比较难复用），可以通过创建完之后先写入磁盘，生成一个没有解码的 UIImage来减少内存的峰值

可以利用 imageIO 实现一个 loadCachedImageWithoutDecode，也可以直接用 [UIImage imageWithData:data] 来实现一样的效果。

- (void)viewDidLoad {
    [super viewDidLoad];
    _imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:_imageView];
    
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(4000, 4000), NO, 1);
    [[UIColor redColor] setFill];
    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, 4000, 4000));
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSData *data = UIImageJPEGRepresentation(img, 0.9);
    
    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
    [data writeToFile:cachePath atomically:YES];
    
//    self.image = [self.class loadCachedImageWithoutDecode];
//    self.image = img;
//    self.image = [UIImage imageWithData:data];
}

+ (nullable UIImage *)loadCachedImageWithoutDecode {
    
    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:cachePath]) {
        
        NSURL *imageUrl = [NSURL fileURLWithPath:cachePath];
        NSDictionary *imageSourceOptions = @{(__bridge id)kCGImageSourceShouldCache : @NO ,
                                             (__bridge id)kCGImageSourceShouldCacheImmediately : @NO};
        CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)imageUrl, (__bridge CFDictionaryRef)imageSourceOptions);
        if (imageSource) {
            NSDictionary *options = @{ (__bridge id)kCGImageSourceShouldCache : @NO ,
                                       (__bridge id)kCGImageSourceTypeIdentifierHint : (id)kUTTypeJPEG,
                                       (__bridge id)kCGImageSourceShouldCacheImmediately : @NO};
            CGImageRef imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, (__bridge CFDictionaryRef)options);
            CFRelease(imageSource);
            
            if (imageRef) {
                return [UIImage imageWithCGImage:imageRef];
            }
        }
    }
    return nil;
}

【10 屏消耗内存】

	20*20	50*50	100*100
空	17 m	4.6m	1.66m
贴一个 imageView	20.9m	5.5m	1.97m
贴一个 UIView	20.5m	5.4m	1.96m

本文测试使用的代码

#import "ViewController.h"
#import <MobileCoreServices/MobileCoreServices.h>

@interface ViewController (){
    int allocatedMB;
    Byte *p[10000];
}
@property (nonatomic) UIImage *image;
@property (nonatomic) UIImageView *imageView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    _imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:_imageView];
    
//    UIImage *img = [self createDecodedImage];
    
//    NSData *data = UIImageJPEGRepresentation(img, 0.9);
//
//    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
//    [data writeToFile:cachePath atomically:YES];
//
//    self.image = [self.class loadCachedImageWithoutDecode];
////    self.image = img;
////    self.image = [UIImage imageWithData:data];
//    [self.class loadCachedImageWithoutDecode];
    [self testCGRasterDataOOM];
}

- (void)testHeepOOM {
    while (1) {
        [NSThread sleepForTimeInterval:0.1];
        [self allocateMemory];
    }
}

- (void)testImageNoReleaseOOM {
    NSMutableArray *arr = [NSMutableArray new];
    while (1) {
        [NSThread sleepForTimeInterval:0.1];
        [arr addObject:[self createDecodedImage]];
    }
}

- (void)testCGRasterDataOOMSmallSize {
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(2, 2), NO, 1);
    NSMutableArray *arr = [NSMutableArray new];
    while (1) {
        [arr addObject:UIGraphicsGetImageFromCurrentImageContext()];
    }
}

- (void)testCGRasterDataOOM {
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(100, 100), NO, 1);
    NSMutableArray *arr = [NSMutableArray new];
    while (1) {
        [NSThread sleepForTimeInterval:0.01];
        [arr addObject:UIGraphicsGetImageFromCurrentImageContext()];
    }
}

- (void)allocateMemory {
    p[allocatedMB] = malloc(10485760);
    memset(p[allocatedMB], 0, 10485760);
    allocatedMB += 1;
}

- (UIImage *)createDecodedImage {
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(4000, 4000), NO, 1);
    [[UIColor redColor] setFill];
    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, 4000, 4000));
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    img = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    return img;
}

+ (nullable UIImage *)loadCachedImageWithoutDecode {
    NSString *cachePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"abc.jpeg"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:cachePath]) {
        
        NSURL *imageUrl = [NSURL fileURLWithPath:cachePath];
        NSDictionary *imageSourceOptions = @{(__bridge id)kCGImageSourceShouldCache : @NO ,
                                             (__bridge id)kCGImageSourceShouldCacheImmediately : @NO};
        CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)imageUrl, (__bridge CFDictionaryRef)imageSourceOptions);
        if (imageSource) {
            NSDictionary *options = @{ (__bridge id)kCGImageSourceShouldCache : @YES ,
                                       (__bridge id)kCGImageSourceTypeIdentifierHint : (id)kUTTypeJPEG,
                                       (__bridge id)kCGImageSourceShouldCacheImmediately : @YES};
            CGImageRef imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, (__bridge CFDictionaryRef)options);
            CFRelease(imageSource);
            
            if (imageRef) {
                return [UIImage imageWithCGImage:imageRef];
            }
        }
    }
    return nil;
}

@end

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