java - 如何考虑垃圾收集器测试内存使用情况？

Question

我正在测试排序算法，我想通过测试 1000 个随机 vector 来测试平均使用的内存。问题是当我在循环内运行大约 20 个随机 vector 时，垃圾收集器运行并且我丢失了计算。请问我该怎么办？我不想手动一一测试=X。

for(int j = 0; j < 1000; j++)
{
    int vetOriginal[] = Generate(); 
    for(int i = 0; i < 10; i++)
    {
        int vetParaTeste[] = vetOriginal.clone();
        long memoriaInicial = Runtime.getRuntime().freeMemory() / 1024;
        mergeSort(vetParaTeste);
        somaMemoriaKB += memoriaInicial - Runtime.getRuntime().freeMemory()/1024;
    }
}
System.out.println("Average memory used: " + somaMemoriaKB / (1000* 10));

Answer 1

好吧，我来晚了一点，你现在可能已经解决了这个问题，但以防万一其他人想知道，防止 GC 清理对象的最简单方法是保留对对象的引用它在另一个对象中。对于您创建的每个对象，将其添加到某种容器中，例如数组/散列/vector/列表或您的语言支持的任何容器。例如:

var items as Array[0..numberOfItems]

for (var i = 0; i < numberOfItems; i++) {
    var vector = createVector()
    items[i] = vector;
}

容器会增加一些开销，因此您需要先测量它，然后从最终输出中减去该量。例如:

var baseMemory = measureMemory()
var numberOfItems = 1000

// create an array of a known size (eg 1000 bytes)
var arrayOfKnownSize as Array[0..numberOfItems]

for (var i = 0; i < numberOfItems; i++)
    arrayOfKnownSize[i] = Int32(0xFF)

// calculate the size occupied by just the data ...
var expectedMemory = sizeOf(Int32) * numberOfItems 

// ... subtract this from the total memory usage and you will get the overhead 
var arrayOverhead = measureMemory() - baseMemory - expectedMemory

// now measure the memory used by an array of vectors
baseMemory = measureMemory()
var vectors as Array[0..numberOfItems]

for (var i = 0; i < numberOfItems; i++) {
    var vector = createVector()
    vectors[i] = vector;
}

// subtract the array overhead from the memory usage
var usedMemory = measureMemory() - baseMemory - arrayOverhead
var averageMemory = usedMemory / numberOfItems

然后，您将进行与之前相同的测量，将每个 vector 插入到数组中，并从内存使用量中减去 arrayOverhead 以获得最终结果。