.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/consensus/agreement/plot_04_partial_synchrony.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_consensus_agreement_plot_04_partial_synchrony.py>`
        to download the full example code or to run this example in your browser via JupyterLite.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_consensus_agreement_plot_04_partial_synchrony.py:


Partial synchrony: timeouts that eventually work (Dwork, Lynch and Stockmeyer 1988)
===================================================================================

Real networks are usually fast but sometimes not. Dwork, Lynch and
Stockmeyer modelled this as partial synchrony: message delays are unbounded
until an unknown Global Stabilization Time (GST), and bounded by an unknown
Delta afterwards. A leader-based protocol keeps safety at all times and
waits out each leader with a timeout. Doubling the timeout every failed view
guarantees it eventually exceeds Delta, whatever Delta is.

What to look for
----------------

Views fail until GST; the first view that starts after GST with a long
enough timeout makes progress. With a fixed timeout below Delta, no view
ever succeeds. PBFT, Tendermint and HotStuff all rely on this model.

The history behind this experiment: :doc:`/history/consensus_breakthroughs`.

.. GENERATED FROM PYTHON SOURCE LINES 23-25

Views before and after GST
--------------------------

.. GENERATED FROM PYTHON SOURCE LINES 25-38

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk

    run = bk.consensus.view_changes(gst=300, delta=40, base_timeout=5)
    print(f"view {run.decided_view} decides at t = {run.decision_time}")
    assert run.view_starts[run.decided_view] >= 300 and run.timeouts[run.decided_view] >= 40

    try:
        bk.consensus.view_changes(gst=0, delta=40, base_timeout=5, growth=1, max_views=100)
    except TimeoutError:
        print("fixed 5-tick timeouts never outlast a 40-tick delay")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    view 6 decides at t = 355
    fixed 5-tick timeouts never outlast a 40-tick delay




.. GENERATED FROM PYTHON SOURCE LINES 39-41

Progress time grows only linearly with GST
------------------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 41-55

.. code-block:: Python

    gsts = list(range(0, 2001, 100))
    decisions = [bk.consensus.view_changes(gst=g, delta=40, base_timeout=5).decision_time for g in gsts]
    assert all(d >= g for d, g in zip(decisions, gsts, strict=True))
    fig, ax = plt.subplots(figsize=(7, 4))
    ax.plot(gsts, decisions, "o-", label="decision time")
    ax.plot(gsts, gsts, "--", color="black", label="GST")
    ax.set(
        xlabel="global stabilization time",
        ylabel="time",
        title="Doubling timeouts: progress soon after GST",
    )
    ax.legend()
    fig.tight_layout()




.. image-sg:: /api/gallery/consensus/agreement/images/sphx_glr_plot_04_partial_synchrony_001.png
   :alt: Doubling timeouts: progress soon after GST
   :srcset: /api/gallery/consensus/agreement/images/sphx_glr_plot_04_partial_synchrony_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 56-61

Exercise
--------
Doubling can overshoot: after a long asynchronous period the timeout may be
far larger than Delta. What does that cost after GST, and why do some
protocols reset the timeout after a successful view?


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.154 seconds)


.. _sphx_glr_download_api_gallery_consensus_agreement_plot_04_partial_synchrony.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: lite-badge

      .. image:: images/jupyterlite_badge_logo.svg
        :target: ../../../../lite/lab/index.html?path=api/gallery/consensus/agreement/plot_04_partial_synchrony.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_04_partial_synchrony.ipynb <plot_04_partial_synchrony.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_04_partial_synchrony.py <plot_04_partial_synchrony.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_04_partial_synchrony.zip <plot_04_partial_synchrony.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_