This speeds up PyCharm's package index processes and avoids CPU & memory overloading

Avoid PyCharm Overloading
=========================

This speeds up PyCharm's package index processes and avoids CPU & memory
overloading.

On my machine (4c/32GB) with 5 conda environments and 10 projects, this reduces
PyCharm's package scanning from 15 minutes to 45 seconds.

Why?
----

When PyCharm has multiple conda environments, it will sometimes launch concurrent
package scanning across those environments. To do so, it uses the `conda` cli,
and a tool called conda_packaging_tool.py, available from the JetBrains
intellij-community github repository (see below).

Unfortunately, these tools do not behave well when launched in parallel, as
they tend to overload CPU & memory in this case.

How?
----

To avoid stalling these processes, we modify their sources as follows:

1. modify the conda cli

    $ conda activate base
    $ pip install runfast
    $ nano `which conda`

    Modify the main section:

     if __name__ == '__main__':
        from conda.cli import main
        from runfast import cached
        cached(main)

2. modify the conda_packaging_tool.py

    if __name__ == '__main__':
        from runfast import cached
        cached(main)

How does this work?
-------------------

Two simple steps:

1. When called in parallel, only one process is allowed to proceed.
2. `runfast.cached` caches the output of these tools (stdout, stderr) for 1 minute,
   given the same command line parameters

That is, when PyCharm launches 5 package scanning (`conda list`) commands, only
one of them will run immediately. If some of the scans are for the same environment,
only one of them will actually run, while the others simply return the same output.

How to clear the cache or avoid caching at all?

    $ export RUNFAST_NOCACHE=1

Testing
-------

a) conda packaging tool

    # first time
    $ time python /opt/pycharm-community-2021.2.1/plugins/python-ce/helpers/conda_packaging_tool.py
    real    0m13.271s
    user    0m9.631s
    sys     0m1.936s

    # second time
    $ time python /opt/pycharm-community-2021.2.1/plugins/python-ce/helpers/conda_packaging_tool.py
    real    0m3.159s
    user    0m0.139s
    sys     0m1.298s

b) conda cli

   # first time
   $ time conda list -p /path/to/env
   real    0m7.985s
   user    0m7.883s
   sys     0m0.087s

   # second time
   real    0m0.152s
   user    0m0.116s
   sys     0m0.032s

References
----------
* https://github.com/JetBrains/intellij-community/blob/master/python/helpers/conda_packaging_tool.py
* https://github.com/conda/conda/blob/33a142c16530fcdada6c377486f1c1a385738a96/conda/core/index.py#L53