NumPy阵列内存管理 [英] Numpy array memory management

问题描述

我对Numpy阵列内存管理有疑问.假设我使用以下命令从缓冲区创建一个numpy数组:

I have a question about Numpy array memory management. Suppose I create a numpy array from a buffer using the following:

>>> s = "abcd"
>>> arr = numpy.frombuffer(buffer(s), dtype = numpy.uint8)
>>> arr.flags
  C_CONTIGUOUS : True
  F_CONTIGUOUS : True
  OWNDATA : False
  WRITEABLE : False
  ALIGNED : True
  UPDATEIFCOPY : False
>>> del s # What happens to arr?

在上述情况下，"arr"是否引用了"s"?如果我删除"s"，这会释放为"s"分配的内存，从而使"arr"潜在地引用未分配的内存吗?

In the situation above, does 'arr' hold a reference to 's'? If I delete 's', will this free the memory allocated for 's' and thus make 'arr' potentially referencing unallocated memory?

我还有其他一些问题:

• 如果这是有效的，Python如何知道何时释放由s分配的内存? gc.get_referrents(arr)函数似乎并不表明'arr'持有对's'的引用.
• 如果这是无效的，我如何将对"s"的引用注册到"arr"中，以便当所有对它的引用都消失时，Python GC会自动获得"s"?

推荐答案

以下内容应使事情澄清一些:

The following should clarify things a little:

>>> s = 'abcd'
>>> arr = np.frombuffer(buffer(s), dtype='uint8')
>>> arr.base
<read-only buffer for 0x03D1BA60, size -1, offset 0 at 0x03D1BA00>
>>> del s
>>> arr.base
<read-only buffer for 0x03D1BA60, size -1, offset 0 at 0x03D1BA00>

在第一种情况下，del s不起作用，因为数组指向的是从中创建的buffer，在其他任何地方均未引用该数组.

In the first case del s has no effect, because what the array is pointing to is a buffer created from it, which is not referenced anywhere else.

>>> t = buffer('abcd')
>>> arr = np.frombuffer(t, dtype='uint8')
>>> arr.base
<read-only buffer for 0x03D1BA60, size -1, offset 0 at 0x03C8D920>
>>> arr.base is t
True
>>> del t
>>> arr.base
<read-only buffer for 0x03D1BA60, size -1, offset 0 at 0x03C8D920>

在第二种情况下，当您使用del t时，您摆脱了指向buffer对象的变量t，但是由于数组仍然具有对该同一buffer的引用，因此不会将其删除.虽然我不确定如何检查它，但是如果您现在del arr，则buffer对象应该丢失其最后一个引用，并会自动进行垃圾收集.

In the second case, when you del t, you get rid of the variable t pointing to the buffer object, but because the array still has a reference to that same buffer, it is not deleted. While I am not sure how to check it, if you now del arr, the buffer object should lose its last reference and be automatically garbage-collected.

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