Package org.python.core.buffer

Class ZeroByteBuffer

java.lang.Object
org.python.core.buffer.BaseBuffer
org.python.core.buffer.Base1DBuffer
org.python.core.buffer.BaseArrayBuffer
org.python.core.buffer.ZeroByteBuffer
All Implemented Interfaces:
AutoCloseable, BufferProtocol, PyBUF, PyBuffer
public class ZeroByteBuffer extends BaseArrayBuffer
Buffer API over a zero length, one-dimensional array of one-byte items. The buffer is nominally writable, but since there is nowhere to write to, any attempt to write or read throws an IndexOutOfBoundsException. This class exists mostly to represent zero-length arrays, and particularly, zero-length slices for which implementations of PyBuffer.getBufferSlice(int, int, int, int) in any case need special logic. Bulk operations like copyTo(byte[], int)) and toString() efficiently do nothing, instead of calling complicated logic that finally does nothing.

  • Constructor Details

    • ZeroByteBuffer

      public ZeroByteBuffer(int flags, BufferProtocol obj, boolean readonly, boolean hasArray) throws PyException
      Construct an instance of a zero-length buffer, choosing whether it should report itself to be read-only through BaseBuffer.isReadonly() or as having a backing array through BaseBuffer.hasArray(). These properties are moot, as any attempt to write to the pretended backing array produces an IndexOutOfBoundsException, but it is less surprising for client code that may ask, if the results are customary for the exporting object.
      Parameters:
      flags - consumer requirements
      obj - exporting object (or null)
      readonly - set true if not to be considered writable
      hasArray - set true if to be considered as backed by an array
      Throws:
      PyException - BufferError when client expectations do not correspond with the type

  • Method Details

    • getLen

      public int getLen()
      Description copied from interface: PyBUF
      The total number of bytes represented by the view, which will be the product of the elements of the shape array, and the item size in bytes.
      Specified by:
      getLen in interface PyBUF
      Overrides:
      getLen in class Base1DBuffer
      Returns:
      the total number of bytes represented.

    • byteIndex

      public int byteIndex(int index) throws IndexOutOfBoundsException
      In a ZeroByteBuffer, the index is always out of bounds.
      Specified by:
      byteIndex in interface PyBuffer
      Overrides:
      byteIndex in class BaseBuffer
      Parameters:
      index - item-index from consumer
      Returns:
      corresponding byte-index in actual storage
      Throws:
      IndexOutOfBoundsException

    • byteIndex

      public int byteIndex(int... indices) throws IndexOutOfBoundsException
      In a ZeroByteBuffer, if the dimensions are right, the index is out of bounds anyway.
      Specified by:
      byteIndex in interface PyBuffer
      Overrides:
      byteIndex in class BaseArrayBuffer
      Parameters:
      indices - n-dimensional item-index from consumer
      Returns:
      corresponding byte-index in actual storage
      Throws:
      IndexOutOfBoundsException

    • copyTo

      public void copyTo(byte[] dest, int destPos) throws IndexOutOfBoundsException
      Copy the contents of the buffer to the destination byte array. The number of bytes will be that returned by PyBUF.getLen(), and the order is the storage order in the exporter. (Note: Correct ordering for multidimensional arrays, including those with indirection needs further study.)

      The default implementation in BaseBuffer deals with the general one-dimensional case of arbitrary item size and stride.

      In a ZeroByteBuffer, there is simply nothing to copy.

      Specified by:
      copyTo in interface PyBuffer
      Overrides:
      copyTo in class BaseBuffer
      Parameters:
      dest - destination byte array
      destPos - byte-index in the destination array of the byte [0]
      Throws:
      IndexOutOfBoundsException - if the destination cannot hold it

    • copyTo

      public void copyTo(int srcIndex, byte[] dest, int destPos, int count) throws IndexOutOfBoundsException, PyException
      Copy a simple slice of the buffer-view to the destination byte array, defined by a starting item-index in the source buffer and the count of items to copy. This may validly be done only for a one-dimensional buffer, as the meaning of the starting item-index is otherwise not defined. count*itemsize bytes will be occupied in the destination.

      The default implementation in BaseBuffer deals with the general one-dimensional case of arbitrary item size and stride, but is unable to optimise access to sequential bytes.

      The implementation in BaseArrayBuffer deals with the general one-dimensional case of arbitrary item size and stride.

      In a ZeroByteBuffer, there is simply nothing to copy.

      Specified by:
      copyTo in interface PyBuffer
      Overrides:
      copyTo in class BaseArrayBuffer
      Parameters:
      srcIndex - starting item-index in the source buffer
      dest - destination byte array
      destPos - byte-index in the destination array of the source item [0,...]
      count - number of items to copy
      Throws:
      IndexOutOfBoundsException - if access out of bounds in source or destination
      PyException

    • copyFrom

      public void copyFrom(byte[] src, int srcPos, int destIndex, int count) throws IndexOutOfBoundsException, PyException
      In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.
      Specified by:
      copyFrom in interface PyBuffer
      Overrides:
      copyFrom in class BaseArrayBuffer
      Parameters:
      src - source byte array
      srcPos - location in source of first byte to copy
      destIndex - starting item-index in the destination (i.e. this)
      count - number of items to copy in
      Throws:
      IndexOutOfBoundsException - if access out of bounds in source or destination
      PyException - TypeError if read-only buffer

    • copyFrom

      public void copyFrom(PyBuffer src) throws IndexOutOfBoundsException, PyException
      In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.
      Specified by:
      copyFrom in interface PyBuffer
      Overrides:
      copyFrom in class BaseArrayBuffer
      Parameters:
      src - source buffer
      Throws:
      IndexOutOfBoundsException - if access out of bounds in source or destination
      PyException - TypeError if read-only buffer

    • getBufferSlice

      public PyBuffer getBufferSlice(int flags, int start, int count)
      Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.
      Specified by:
      getBufferSlice in interface PyBuffer
      Overrides:
      getBufferSlice in class BaseBuffer
      Parameters:
      flags - specifying features demanded and the navigational capabilities of the consumer
      start - index in the current buffer
      count - number of items in the required slice
      Returns:
      a buffer representing the slice

    • getBufferSlice

      public PyBuffer getBufferSlice(int flags, int start, int count, int stride)
      Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.
      Parameters:
      flags - specifying features demanded and the navigational capabilities of the consumer
      start - index in the current buffer
      count - number of items in the required slice
      stride - index-distance in the current buffer between consecutive items in the slice
      Returns:
      a buffer representing the slice

    • getBuf

      public PyBuffer.Pointer getBuf()
      Return a structure describing the slice of a byte array that holds the data being exported to the consumer. For a one-dimensional contiguous buffer, assuming the following client code where obj has type BufferProtocol: 
       PyBuffer a = obj.getBuffer(PyBUF.SIMPLE);
 int itemsize = a.getItemsize();
 PyBuffer.Pointer b = a.getBuf();
      the item with index k is in the array b.storage at index [b.offset + k*itemsize] to [b.offset + (k+1)*itemsize - 1] inclusive. And if itemsize==1, the item is simply the byte b.storage[b.offset + k]

      If the buffer is multidimensional or non-contiguous, storage[offset] is still the (first byte of) the item at index [0] or [0,...,0]. However, it is necessary to navigate b.storage using the shape, strides and maybe suboffsets provided by the API.

      BaseArrayBuffer provides a reference to the storage array even when the buffer is intended not to be writable. There can be no enforcement of read-only character once a reference to the byte array has been handed out.

      The implementation in ZeroByteBuffer efficiently returns an empty buffer.

      Specified by:
      getBuf in interface PyBuffer
      Overrides:
      getBuf in class BaseArrayBuffer
      Returns:
      structure defining the byte[] slice that is the shared data

    • toString

      public String toString()
      For a ZeroByteBuffer, it's the empty string.
      Specified by:
      toString in interface PyBuffer
      Overrides:
      toString in class BaseBuffer