src/nmutil/dynamicpipe.py

   1 # SPDX-License-Identifier: LGPL-2.1-or-later
   2 # See Notices.txt for copyright information
   3
   4 """ Meta-class that allows a dynamic runtime parameter-selectable "mixin"
   5
   6 The reasons why this technique is being deployed is because SimpleHandshake
   7 needs to be dynamically replaced at the end-users' choice, without having
   8 to duplicate dozens of classes using multiple-inheritanc "Mix-in" techniques.
   9
  10 It is however extremely unusual, and has been explicitly limited to this *one*
  11 module.  DO NOT try to use this technique elsewhere, it is extremely hard to
  12 understand (meta-class programming).
  13
  14 """
  15
  16 from abc import ABCMeta
  17
  18 from nmutil.singlepipe import SimpleHandshake
  19 import threading
  20
  21 # with many thanks to jsbueno on stackexchange for this one
  22 # https://stackoverflow.com/questions/57273070/
  23 # list post:
  24 # http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-July/002259.html
  25
  26 class Meta(ABCMeta):
  27     registry = {}
  28     recursing = threading.local()
  29     recursing.check = False
  30     mlock = threading.Lock()
  31
  32     def __call__(cls, *args, **kw):
  33         mcls = cls.__class__
  34         if mcls.recursing.check:
  35             return super().__call__(*args, **kw)
  36         spec = args[0]
  37         base = spec.pipekls # pick up the dynamic class from PipelineSpec, HERE
  38
  39         if (cls, base) not in mcls.registry:
  40             print ("__call__", args, kw, cls, base,
  41                    base.__bases__, cls.__bases__)
  42             mcls.registry[cls, base] = type(
  43                 cls.__name__,
  44                 (cls, base) + cls.__bases__[1:],
  45                 {}
  46             )
  47         real_cls = mcls.registry[cls, base]
  48
  49         with mcls.mlock:
  50             mcls.recursing.check = True
  51             instance = real_cls.__class__.__call__(real_cls, *args, **kw)
  52             mcls.recursing.check = False
  53         return instance
  54
  55
  56 # Inherit from this class instead of SimpleHandshake (or other ControlBase
  57 # derivative), and the metaclass will instead *replace* DynamicPipe -
  58 # *at runtime* - with the class that is specified *as a parameter*
  59 # in PipelineSpec.
  60 #
  61 # as explained in the list posting and in the stackexchange post, this is
  62 # needed to avoid a MASSIVE suite of duplicated multiple-inheritance classes
  63 # that "Mix in" SimpleHandshake (or other).
  64 #
  65 # unfortunately, composition does not work in this instance
  66 # (make an *instance* of SimpleHandshake or other class and pass it in)
  67 # due to the multiple level inheritance, and in several places
  68 # the inheriting class needs to do some setup that the deriving class
  69 # needs in order to function correctly.
  70
  71 class DynamicPipe(metaclass=Meta):
  72     def __init__(self, *args):
  73         print ("DynamicPipe init", super(), args)
  74         super().__init__(self, *args)
  75
  76
  77 # bad hack: the DynamicPipe metaclass ends up creating an __init__ signature
  78 # for the dynamically-derived class.  luckily, SimpleHandshake only needs
  79 # "self" as the 1st argument (it is its own "Stage").  anything else
  80 # could hypothetically be passed through the pspec.
  81 class SimpleHandshakeRedir(SimpleHandshake):
  82     def __init__(self, mod, *args):
  83         print ("redir", mod, args)
  84         stage = self
  85         if args and args[0].stage:
  86             stage = args[0].stage
  87         SimpleHandshake.__init__(self, stage)
  88