Interface PyBuffer

Method Details

• getObj

  BufferProtocol getObj()

  Return the underlying exporting object (or null if no object implementing the BufferProtocol is in that role). This will often be a PyObject.

  Returns:

  exporting object (or null)

• byteAt

  byte byteAt(int index) throws IndexOutOfBoundsException

  Return the byte indexed from a one-dimensional buffer with item size one. This is part of the fully-encapsulated API: the buffer implementation exported takes care of navigating the structure of the buffer. Results are undefined where the number of dimensions is not one or if itemsize>1.

  Parameters:

  index - to retrieve from

  Returns:

  the item at index, which is a byte

  Throws:

  IndexOutOfBoundsException

• intAt

  int intAt(int index) throws IndexOutOfBoundsException

  Return the unsigned byte value indexed from a one-dimensional buffer with item size one. This is part of the fully-encapsulated API: the exporter takes care of navigating the structure of the buffer. Results are undefined where the number of dimensions is not one or if itemsize>1.

  Parameters:

  index - to retrieve from

  Returns:

  the item at index, treated as an unsigned byte, =0xff & byteAt(index)

  Throws:

  IndexOutOfBoundsException

• storeAt

  void storeAt(byte value, int index) throws IndexOutOfBoundsException

  Store the given byte at the indexed location in of a one-dimensional buffer with item size one. This is part of the fully-encapsulated API: the buffer implementation exported takes care of navigating the structure of the buffer. Results are undefined where the number of dimensions is not one or if itemsize>1.

  Parameters:

  value - to store

  index - to location

  Throws:

  IndexOutOfBoundsException

• byteAt

  byte byteAt(int... indices) throws IndexOutOfBoundsException

  Return the byte indexed from an N-dimensional buffer with item size one. This is part of the fully-encapsulated API: the buffer implementation exported takes care of navigating the structure of the buffer. The indices must be correct in number and range for the array shape. Results are undefined where itemsize>1.

  Parameters:

  indices - specifying location to retrieve from

  Returns:

  the item at location, which is a byte

  Throws:

  IndexOutOfBoundsException

• intAt

  int intAt(int... indices) throws IndexOutOfBoundsException

  Return the unsigned byte value indexed from an N-dimensional buffer with item size one. This is part of the fully-encapsulated API: the buffer implementation exported takes care of navigating the structure of the buffer. The indices must be correct in number and range for the array shape. Results are undefined where itemsize>1.

  Parameters:

  indices - specifying location to retrieve from

  Returns:

  the item at location, treated as an unsigned byte, =0xff & byteAt(index)

  Throws:

  IndexOutOfBoundsException

• storeAt

  void storeAt(byte value, int... indices) throws IndexOutOfBoundsException

  Store the given byte at the indexed location in of an N-dimensional buffer with item size one. This is part of the fully-encapsulated API: the exporter takes care of navigating the structure of the buffer. The indices must be correct in number and range for the array shape. Results are undefined where itemsize>1.

  Parameters:

  value - to store

  indices - specifying location to store at

  Throws:

  IndexOutOfBoundsException

• copyTo

  void copyTo(byte[] dest, int destPos) throws IndexOutOfBoundsException, PyException

  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.)

  Parameters:

  dest - destination byte array

  destPos - byte-index in the destination array of the byte [0]

  Throws:

  IndexOutOfBoundsException - if the destination cannot hold it

  PyException

• copyTo

  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.

  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

  void copyFrom(byte[] src, int srcPos, int destIndex, int count) throws IndexOutOfBoundsException, PyException

  Copy from a slice of a (Java) byte array into the buffer starting at a given destination item-index. This may validly be done only for a one-dimensional buffer, as the meaning of the destination index is not otherwise defined. count*itemsize bytes will be read from the source.

  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

  void copyFrom(PyBuffer src) throws IndexOutOfBoundsException, PyException

  Copy the whole of another PyBuffer into this buffer. This may validly be done only for buffers that are consistent in their dimensions. When it is necessary to copy partial buffers, this may be achieved using a buffer slice on the source or destination.

  Parameters:

  src - source buffer

  Throws:

  IndexOutOfBoundsException - if access out of bounds in source or destination

  PyException - TypeError if read-only buffer

• getBuffer

  PyBuffer getBuffer(int flags) throws PyException

  Method by which the consumer requests the buffer from the exporter. The consumer provides information on its ability to understand buffer navigation. Each consumer requesting a buffer in this way, when it has finished using it, should make a corresponding call to release() on the buffer it obtained, or close() using try-with-resources, since some objects alter their behaviour while buffers are exported.

  When a PyBuffer is the target, the same checks are carried out on the consumer flags, and a return will normally be a reference to that buffer. A Jython PyBuffer keeps count of these re-exports in order to match them with the number of calls to release(). When the last matching release() arrives it is considered "final", and release actions may then take place on the exporting object. After the final release of a buffer, a call to getBuffer should raise an exception.

  Specified by:

  getBuffer in interface BufferProtocol

  Parameters:

  flags - specifying features demanded and the navigational capabilities of the consumer

  Returns:

  exported buffer

  Throws:

  PyException - BufferError when expectations do not correspond with the buffer

• release

  void release()

  A buffer is (usually) a view onto to the internal state of an exporting object, and that object may have to restrict its behaviour while the buffer exists. The consumer must therefore say when it has finished with the buffer if the exporting object is to be released from this constraint. Each consumer that obtains a reference to a buffer by means of a call to BufferProtocol.getBuffer(int) or getBuffer(int) should make a matching call to release(). The consumer may be sharing the PyBuffer with other consumers and the buffer uses the pairing of getBuffer and release to manage the lock on behalf of the exporter. It is an error to make more than one call to release for a single call to getBuffer.

• close

  void close()

  An alias for release() to satisfy AutoCloseable.

  Specified by:

  close in interface AutoCloseable

• isReleased

  boolean isReleased()

  True only if the buffer has been released with (the required number of calls to) release() or some equivalent operation. The consumer may be sharing the reference with other consumers and the buffer only achieves the released state when all consumers who called getBuffer have called release.

• getBufferSlice

  PyBuffer getBufferSlice(int flags, int start, int count)

  Equivalent to getBufferSlice(int, int, int, int) with stride 1.

  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

  PyBuffer getBufferSlice(int flags, int start, int count, int stride)

  Get a PyBuffer that represents a slice of the current one described in terms of a start index, number of items to include in the slice, and the stride in the current buffer. A consumer that obtains a PyBuffer with getBufferSlice must release it with release() just as if it had been obtained with getBuffer(int)

  Suppose that x(i) denotes the ith element of the current buffer, that is, the byte retrieved by this.byteAt(i) or the unit indicated by this.getPointer(i). A request for a slice where start = s, count = N and stride = m, results in a buffer y such that y(k) = x(s+km) where k=0..(N-1). In Python terms, this is the slice x[s : s+(N-1)m+1 : m] (if m>0) or the slice x[s : s+(N-1)m-1 : m] (if m<0). Implementations should check that this range is entirely within the current buffer.

  In a simple buffer backed by a contiguous byte array, the result is a strided PyBuffer on the same storage but where the offset is adjusted by s and the stride is as supplied. If the current buffer is already strided and/or has an item size larger than single bytes, the new start index, count and stride will be translated from the arguments given, through this buffer's stride and item size. The caller always expresses start and strides in terms of the abstract view of this buffer.

  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

• byteIndex

  int byteIndex(int index) throws IndexOutOfBoundsException

  Convert an item index (for a one-dimensional buffer) to an absolute byte index in the storage shared by the exporter. The storage exported as a PyBuffer is a linearly-indexed sequence of bytes, although it may not actually be a heap-allocated Java byte[] object. The purpose of this method is to allow the exporter to define the relationship between the item index (as used in byteAt(int)) and the byte-index (as used with the ByteBuffer returned by getNIOByteBuffer()). See byteIndex(int[]) for discussion of the multi-dimensional case.

  Parameters:

  index - item-index from consumer

  Returns:

  corresponding byte-index in actual storage

  Throws:

  IndexOutOfBoundsException

• byteIndex

  int byteIndex(int... indices)

  Convert a multi-dimensional item index to an absolute byte index in the storage shared by the exporter. The storage exported as a PyBuffer is a linearly-indexed sequence of bytes, although it may not actually be a heap-allocated Java byte[] object. The purpose of this method is to allow the exporter to define the relationship between the item index (as used in byteAt(int...) and the byte-index (as used with the ByteBuffer returned by getNIOByteBuffer()).

  Parameters:

  indices - n-dimensional item-index from consumer

  Returns:

  corresponding byte-index in actual storage

• getNIOByteBuffer

  ByteBuffer getNIOByteBuffer()

  Obtain a ByteBuffer giving access to the bytes that hold the data being exported by the original object. The position of the buffer is at the first byte of the item with zero index (quite possibly not the lowest valid byte-index), the limit of the buffer is beyond the largest valid byte index, and the mark is undefined.

  For a one-dimensional contiguous buffer, the limit is one byte beyond the last item, so that consecutive reads from the ByteBuffer return the data in order. Assuming the following client code where obj has type BufferProtocol:

   PyBuffer a = obj.getBuffer(PyBUF.SIMPLE);
   int itemsize = a.getItemsize();
   ByteBuffer bb = a.getNIOBuffer();
   

  the item with index k is in bb at positions bb.pos()+k*itemsize to bb.pos()+(k+1)*itemsize - 1 inclusive. And if itemsize==1, the item is simply the byte at position bb.pos()+k.

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

  Returns:

  a ByteBuffer onto the exported data contents.

• hasArray

  boolean hasArray()

  Report whether the exporter is able to offer direct access to the exported storage as a Java byte array (through the API that involves class PyBuffer.Pointer), or only supports the abstract API. See also PyBUF.AS_ARRAY.

  Returns:

  true if array access is supported, false if it is not.

• getBuf

  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.

  Returns:

  structure defining the byte[] slice that is the shared data

• getPointer

  PyBuffer.Pointer getPointer(int index)

  Return a structure describing the position in a byte array of a single item from the data being exported to the consumer. For a one-dimensional contiguous buffer, assuming the following client code where obj has type BufferProtocol:

   int k = ... ;
   PyBuffer a = obj.getBuffer(PyBUF.FULL);
   int itemsize = a.getItemsize();
   PyBuffer.Pointer b = a.getPointer(k);
   

  the item with index k is in the array b.storage at index [b.offset] to [b.offset + itemsize - 1] inclusive. And if itemsize==1, the item is simply the byte b.storage[b.offset]

  Essentially this is a method for computing the offset of a particular index. The client is free to navigate the underlying buffer b.storage without respecting these boundaries.

  Parameters:

  index - in the buffer to position the pointer

  Returns:

  structure defining the byte[] slice that is the shared data

• getPointer

  PyBuffer.Pointer getPointer(int... indices)

  Return a structure describing the position in a byte array of a single item from the data being exported to the consumer, in the case that array may be multi-dimensional. For a 3-dimensional contiguous buffer, assuming the following client code where obj has type BufferProtocol:

   int i, j, k;
   // ... calculation that assigns i, j, k
   PyBuffer a = obj.getBuffer(PyBUF.FULL);
   int itemsize = a.getItemsize();
   PyBuffer.Pointer b = a.getPointer(i,j,k);
   

  the item with index [i,j,k] is in the array b.storage at index [b.offset] to [b.offset + itemsize - 1] inclusive. And if itemsize==1, the item is simply the byte b.storage[b.offset]

  Essentially this is a method for computing the offset of a particular index. The client is free to navigate the underlying buffer b.storage without respecting these boundaries. If the buffer is non-contiguous, the above description is still valid (since a multi-byte item must itself be contiguously stored), but in any additional navigation of b.storage[] to other items, the client must use the shape, strides and sub-offsets provided by the API. Normally one starts b = a.getBuf() in order to establish the offset of index [0,...,0].

  Parameters:

  indices - multidimensional index at which to position the pointer

  Returns:

  structure defining the byte[] slice that is the shared data

• getFormat

  String getFormat()

  A format string in the language of Python structs describing how the bytes of each item should be interpreted. Irrespective of the PyBUF.FORMAT bit in the consumer's call to getBuffer, a valid format string is always returned (difference from CPython).

  Jython only implements "B" so far, and it is debatable whether anything fancier than "<n>B" can be supported in Java.

  Returns:

  the format string

• toString

  String toString()

  The toString() method of a buffer reproduces the byte values in the buffer (treated as unsigned integers) as the character codes of a String.

  Overrides:

  toString in class Object