考虑到垃圾收集器，如何测试使用的内存？

Question

我正在测试一种排序算法，我想通过测试 1000 个随机向量来测试平均使用内存。问题是当我在循环中运行大约 20 个随机向量时，垃圾收集器运行并且我失去了计算。请问我该怎么办？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

好的，所以我来晚了一点，您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/哈希/向量/列表或您的语言支持的任何内容。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，因此您需要先对其进行测量，然后从最终输出中减去该数量。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，您将执行与之前相同的测量，将每个向量插入一个数组并从内存使用量中减去 arrayOverhead 以获得最终结果。