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DvG_RingBuffer

Provides a numpy ring buffer at a fixed memory address to allow for significantly sped up numpy, sigpy, numba & pyFFTW calculations.

• Github: https://github.com/Dennis-van-Gils/python-dvg-ringbuffer
• PyPI: https://pypi.org/project/dvg-ringbuffer

Installation::

pip install dvg-ringbuffer

Based on:

https://pypi.org/project/numpy_ringbuffer/ by Eric Wieser.

``DvG_RingBuffer`` can be used as a drop-in replacement for
``numpy_ringbuffer`` and provides several optimizations and extra features,
but requires Python 3.

If and only if the ring buffer is completely full, will it return its array data as a contiguous C-style numpy array at a single fixed memory address per ring buffer instance. It does so by unwrapping the discontiguous ring buffer array into a second extra unwrap buffer that is a private member of the ring buffer class. This is advantegeous for other accelerated computations by, e.g., numpy, sigpy, numba & pyFFTW, that benefit from being fed with contiguous arrays at the same memory address each time again, such that compiler optimizations and data planning are made possible.

When the ring buffer is not completely full, it will return its data as a contiguous C-style numpy array, but at different memory addresses. This is how the original numpy-buffer always operates.

Commonly, collections.deque() is used to act as a ring buffer. The benefits of a deque is that it is thread safe and fast (enough) for most situations. However, there is an overhead whenever the deque -- a list-like container -- needs to be transformed into a numpy array. Because DvG_RingBuffer already returns numpy arrays it will outperform a collections.deque() easily, tested to be a factor of ~60.

.. warning::

* This ring buffer is not thread safe. You'll have to implement your own
  mutex locks when using this ring buffer in multithreaded operations.

* The data array that is returned by a full ring buffer is a pass by
  reference of the *unwrap* buffer. It is not a copy! Hence, changing
  values in the returned data array is identical to changing values in the
  *unwrap* buffer.

API

class RingBuffer(capacity, dtype=np.float64, allow_overwrite=True)

Create a new ring buffer with the given capacity and element type.

    Args:
        capacity (``int``):
            The maximum capacity of the ring buffer

        dtype (``data-type``, optional):
            Desired type of buffer elements. Use a type like ``(float, 2)``
            to produce a buffer with shape ``(capacity, 2)``.

            Default: ``np.float64``

        allow_overwrite (``bool``, optional):
            If ``False``, throw an IndexError when trying to append to an
            already full buffer.

            Default: ``True``

Methods

• clear()

• append(value) Append a single value to the ring buffer.

  .. code-block:: python

  rb = RingBuffer(3, dtype=np.int)  #  []
  rb.append(1)                      #  [1]
  rb.append(2)                      #  [1, 2]
  rb.append(3)                      #  [1, 2, 3]
  rb.append(4)                      #  [2, 3, 4]

• appendleft(value) Append a single value to the ring buffer from the left side.

  .. code-block:: python

  rb = RingBuffer(3, dtype=np.int)  #  []
  rb.appendleft(1)                  #  [1]
  rb.appendleft(2)                  #  [2, 1]
  rb.appendleft(3)                  #  [3, 2, 1]
  rb.appendleft(4)                  #  [4, 3, 2]

• extend(values) Extend the ring buffer with a list of values.

  .. code-block:: python

  rb = RingBuffer(3, dtype=np.int)  #  []
  rb.extend([1])                    #  [1]
  rb.extend([2, 3])                 #  [1, 2, 3]
  rb.extend([4, 5, 6, 7])           #  [5, 6, 7]

• extendleft(values) Extend the ring buffer with a list of values from the left side.

  .. code-block:: python

  rb = RingBuffer(3, dtype=np.int)  #  []
  rb.extendleft([1])                #  [1]
  rb.extendleft([3, 2])             #  [3, 2, 1]
  rb.extendleft([7, 6, 5, 4])       #  [7, 6, 5]

• pop() Remove the right-most item from the ring buffer and return it.

• popleft() Remove the left-most item from the ring buffer and return it.

Properties

• is_full
• unwrap_address
• current_address
• dtype
• shape
• maxlen

Indexing & slicing

• [] including negative indices and slicing

  .. code-block:: python

  from dvg_ringbuffer import RingBuffer
  
  rb = RingBuffer(4, dtype=np.int)  # --> rb[:] = array([], dtype=int32)
  rb.extend([1, 2, 3, 4, 5])        # --> rb[:] = array([2, 3, 4, 5])
  x = rb[0]                         # --> x = 2
  x = rb[-1]                        # --> x = 5
  x = rb[:3]                        # --> x = array([2, 3, 4])
  x = rb[np.array([0, 2, -1])]      # --> x = array([2, 4, 5])
  
  rb = RingBuffer(5, dtype=(np.int, 2))  # --> rb[:] = array([], shape=(0, 2), dtype=int32)
  rb.append([1, 2])                      # --> rb[:] = array([[1, 2]])
  rb.append([3, 4])                      # --> rb[:] = array([[1, 2], [3, 4]])
  rb.append([5, 6])                      # --> rb[:] = array([[1, 2], [3, 4], [5, 6]])
  x = rb[0]                              # --> x = array([1, 2])
  x = rb[0, :]                           # --> x = array([1, 2])
  x = rb[:, 0]                           # --> x = array([1, 3, 5])