Swift 3 CGImage 内存问题

Question

我的 Swift3 代码中有这个函数，实际上我几乎是从 Apple 示例代码中翻译过来的。

我的应用程序处理来自从摄像头捕获实时馈送的 sampleBuffers。

此函数正确地从 CMSampleBuffer 创建并返回图像。 它工作正常，但内存一直在增长，直到应用程序崩溃。

通过 Instruments，我看到有一些图像数据没有发布。 如果我评论我执行“context.makeImage”的行，内存就会保持不变。阅读该 func 文档，它说它从上下文中复制数据。所以我在想有一些数据被复制了，一个副本没有发布。

“问题”是 Swift 自动处理 CoreFoundations 内存保留/释放，所以我没有办法处理它。

如您所见，我尝试使用自动释放池，但它不起作用。

有什么想法吗？

谢谢

func image(from sampleBuffer:CMSampleBuffer) -> UIImage?{

    /* https://developer.apple.com/library/content/qa/qa1702/_index.html */
    let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)

    guard imageBuffer != nil else{
        return nil
    }

    return autoreleasepool{ () -> UIImage in

        CVPixelBufferLockBaseAddress(imageBuffer!, .readOnly);

        let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer!)

        // Get the number of bytes per row for the pixel buffer
        let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer!);
        // Get the pixel buffer width and height
        let width = CVPixelBufferGetWidth(imageBuffer!);
        let height = CVPixelBufferGetHeight(imageBuffer!);

        let colorSpace = CGColorSpaceCreateDeviceRGB();

        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)
            .union(.byteOrder32Little)

        // Create a bitmap graphics context with the sample buffer data
        let context = CGContext(data: baseAddress, width: width, height: height, bitsPerComponent: 8,
                                bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue);

        // Create a Quartz image from the pixel data in the bitmap graphics context
        let quartzImage = context!.makeImage();
        // Unlock the pixel buffer
        CVPixelBufferUnlockBaseAddress(imageBuffer!,.readOnly);

        let image = UIImage(cgImage: quartzImage!)

        return image
    }
}

Answer 1

与其他 Core* libraries which are not ARC compliant 一样，您可能需要将 CM 调用包装在 autorelease 中。

func image(from sampleBuffer:CMSampleBuffer) -> UIImage?{
 

    var ret: UIImage?
    autoreleasepool {

        /* https://developer.apple.com/library/content/qa/qa1702/_index.html */
        let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)


        CVPixelBufferLockBaseAddress(imageBuffer!, .readOnly);

        let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer!)

        // Get the number of bytes per row for the pixel buffer
        let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer!);
        // Get the pixel buffer width and height
        let width = CVPixelBufferGetWidth(imageBuffer!);
        let height = CVPixelBufferGetHeight(imageBuffer!);

        let colorSpace = CGColorSpaceCreateDeviceRGB();

        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)
            .union(.byteOrder32Little)

        // Create a bitmap graphics context with the sample buffer data
        let context = CGContext(data: baseAddress, width: width, height: height, bitsPerComponent: 8,
                                bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue);

        // Create a Quartz image from the pixel data in the bitmap graphics context
        let quartzImage = context!.makeImage();
        // Unlock the pixel buffer
        CVPixelBufferUnlockBaseAddress(imageBuffer!,.readOnly);

        let image = UIImage(cgImage: quartzImage!)

        ret = image
    }
    return ret
}

详情请见this answer。

Answer 2

我找到了解决问题的方法。

我不知道 UIKit 不是线程安全的。似乎在与主线程不同的线程中执行该代码不允许系统按应有的方式释放内存。

在主线程上，内存被正确释放和管理。