Swift 5 MacOS 图像调整大小内存问题

我是使用 Swift 进行 Mac OS 应用程序开发的新手。但我尝试制作简单的 ImageResizer 应用程序。我必须调整 50k 图像的大小。 10个小时后，内存已增加到近120GB。我以为 Swift 也有垃圾收集器。为什么它可以增加记忆力？我会告诉你我的代码。

for i in 0..<paths.count {
    let path = paths[i]

    if let image = NSImage(contentsOf: path) {
        ...

        if self.resize(image: image, size: size, to: URL(fileURLWithPath: resizedImagePath)) {
            print("Image saved to \(resizedImagePath)")
            continue
        }
    }
}

func resize(image: NSImage, size: Int, to url: URL) -> Bool {
    if !image.isValid {
        print("invalid image")
        return false
    }

    guard let pixelsWide = image.representations.first?.pixelsWide else {
        return false
    }

    let factor: CGFloat = CGFloat(pixelsWide) / image.size.width

    var width: CGFloat = CGFloat(size)
    var height: CGFloat = CGFloat(size)
    if image.size.width > image.size.height {
        height = width * image.size.height / image.size.width
    } else {
        width = height * image.size.width / image.size.height
    }

    let rep = NSBitmapImageRep(bitmapDataPlanes: nil,
                               pixelsWide: Int(width),
                               pixelsHigh: Int(height),
                               bitsPerSample: 8,
                               samplesPerPixel: 4,
                               hasAlpha: true,
                               isPlanar: false,
                               colorSpaceName: .deviceRGB,
                               bytesPerRow: Int(width * 4),
                               bitsPerPixel: 32)
    rep?.size = NSSize(width: width / factor, height: height / factor)

    let ctx = NSGraphicsContext(bitmapImageRep: rep!)
    NSGraphicsContext.saveGraphicsState()
    NSGraphicsContext.current = ctx
    image.draw(in: NSMakeRect(0, 0, width / factor, height / factor))
    ctx?.flushGraphics()
    NSGraphicsContext.restoreGraphicsState()

    // Get NSData, and save it
    let data = rep?.representation(using: .png, properties: [:]) // properties as! [String : Any]) //
    do {
        try data?.write(to: url)
        return true
    }
    catch {
        return false
    }
}

您可以将循环内的整个代码放入自动释放池 https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmAutoreleasePools.html:

如果您编写一个创建许多临时对象的循环。您可以使用 循环内的自动释放池块用于处理这些对象 在下一次迭代之前。在循环中使用自动释放池块 有助于减少应用程序的最大内存占用。

for i in paths.indices {
    autoreleasepool {
        // all your image resizing code goes here
    }
}