mirror of https://github.com/Qiskit/qiskit.git
37 lines
2.1 KiB
YAML
37 lines
2.1 KiB
YAML
---
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features:
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- |
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The user config file has 2 new configuration options, ``num_processes`` and
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``parallel``, which are used to control the default behavior of
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:func:`~qiskit.tools.parallel_map`. The ``parallel`` option is a boolean
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that is used to dictate whether :func:`~qiskit.tools.parallel_map` will
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run in multiple processes or not. If it set to ``False`` calls to
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:func:`~qiskit.tools.parallel_map` will be executed serially, while setting
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it to ``True`` will enable parallel execution. The ``num_processes`` option
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takes an integer which sets how many CPUs to use when executing in parallel.
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By default it will use the number of CPU cores on a system.
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There are 2 new environment variables, ``QISKIT_PARALLEL`` and
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``QISKIT_NUM_PROCS``, that can be used to control the default behavior of
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:func:`~qiskit.tools.parallel_map`. The ``QISKIT_PARALLEL`` option can be
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set to the ``TRUE`` (any capitalization) to set the default to run in
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multiple processes when :func:`~qiskit.tools.parallel_map` is called. If it
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is set to any other
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value :func:`~qiskit.tools.parallel_map` will be executed serially.
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``QISKIT_NUM_PROCS`` takes an integer (for example ``QISKIT_NUM_PROCS=5``)
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which will be used as the default number of processes to run with. Both
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of these will take precedence over the equivalent option set in the user
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config file.
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upgrade:
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By default on macOS with Python >=3.8 :func:`~qiskit.tools.parallel_map`
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will no longer run in multiple processes. This is a change from previous
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releases where the default behavior was that
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:func:`~qiskit.tools.parallel_map` would launch multiple processes. This
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change was made because with newer versions of macOS with Python 3.8 and
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3.9 multiprocessing is either unreliable or adds significant overhead
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because of the change in Python 3.8 to launch new processes with ``spawn``
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instead of ``fork``. To re-enable parallel execution on macOS with
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Python >= 3.8 you can use the user config file ``parallel`` option or set
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the environment variable ``QISKIT_PARALLEL`` to ``True``.
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