在后台运行coreml时发生错误:计算NN输出错误时出错 [英] Error when running coreml in the background: Error computing NN outputs error

问题描述

我正在运行来自iPhone 6上的keras的mlmodel.预测经常失败，并出现错误计算NN输出错误.有人知道原因是什么吗，如果我能做些什么呢?

I'm running an mlmodel that is coming from keras on an iPhone 6. The predictions often fails with the error Error computing NN outputs. Does anyone know what could be the cause and if there is anything I can do about it?

do {
    return try model.prediction(input1: input)
} catch let err {
    fatalError(err.localizedDescription) // Error computing NN outputs error
}

编辑:我尝试了苹果公司的示例项目，那个是在后台运行的，所以它似乎特定于我们的项目或模型类型.

I tried apple's sample project and that one works in the background so it seems it's specific to either our project or model type.

推荐答案

最后，对于我们来说，设置 usesCPUOnly 标志就足够了.在iOS中似乎禁止在后台使用GPU.苹果实际上也在他们的文档中对此进行了写道..为了指定这个标志，我们不能再使用生成的模型类，而不得不调用原始的coreml类.我可以想象在将来的版本中这种变化.以下代码段摘自生成的模型类，但指定了添加的 MLPredictionOptions .

In the end it was enough for us to set the usesCPUOnly flag. Using the GPU in the background seems prohibited in iOS. Apple actually wrote about this in their documentation as well. To specify this flag we couldn't use the generated model class anymore but had to call the raw coreml classes instead. I can imagine this changing in a future version however. The snippet below is taken from the generated model class, but with the added MLPredictionOptions specified.

let options = MLPredictionOptions()
options.usesCPUOnly = true // Can't use GPU in the background

// Copied from from the generated model class
let input = model_input(input: mlMultiArray)
let output = try generatedModel.model.prediction(from: input, options: options)
let result = model_output(output: output.featureValue(for: "output")!.multiArrayValue!).output

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