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 from nmutil.singlepipe import MaskCancellable
  20
  21 import threading
  22
  23 # with many thanks to jsbueno on stackexchange for this one
  24 # https://stackoverflow.com/questions/57273070/
  25 # list post:
  26 # http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-July/002259.html
  27
  28 class Meta(ABCMeta):
  29     registry = {}
  30     recursing = threading.local()
  31     recursing.check = False
  32     mlock = threading.Lock()
  33
  34     def __call__(cls, *args, **kw):
  35         mcls = cls.__class__
  36         if mcls.recursing.check:
  37             return super().__call__(*args, **kw)
  38         spec = args[0]
  39         base = spec.pipekls # pick up the dynamic class from PipelineSpec, HERE
  40
  41         if (cls, base) not in mcls.registry:
  42             print ("__call__", args, kw, cls, base,
  43                    base.__bases__, cls.__bases__)
  44             mcls.registry[cls, base] = type(
  45                 cls.__name__,
  46                 (cls, base) + cls.__bases__[1:],
  47                 {}
  48             )
  49         real_cls = mcls.registry[cls, base]
  50
  51         with mcls.mlock:
  52             mcls.recursing.check = True
  53             instance = real_cls.__class__.__call__(real_cls, *args, **kw)
  54             mcls.recursing.check = False
  55         return instance
  56
  57
  58 # Inherit from this class instead of SimpleHandshake (or other ControlBase
  59 # derivative), and the metaclass will instead *replace* DynamicPipe -
  60 # *at runtime* - with the class that is specified *as a parameter*
  61 # in PipelineSpec.
  62 #
  63 # as explained in the list posting and in the stackexchange post, this is
  64 # needed to avoid a MASSIVE suite of duplicated multiple-inheritance classes
  65 # that "Mix in" SimpleHandshake (or other).
  66 #
  67 # unfortunately, composition does not work in this instance
  68 # (make an *instance* of SimpleHandshake or other class and pass it in)
  69 # due to the multiple level inheritance, and in several places
  70 # the inheriting class needs to do some setup that the deriving class
  71 # needs in order to function correctly.
  72
  73 class DynamicPipe(metaclass=Meta):
  74     def __init__(self, *args):
  75         print ("DynamicPipe init", super(), args)
  76         super().__init__(self, *args)
  77
  78
  79 # bad hack: the DynamicPipe metaclass ends up creating an __init__ signature
  80 # for the dynamically-derived class.  luckily, SimpleHandshake only needs
  81 # "self" as the 1st argument (it is its own "Stage").  anything else
  82 # could hypothetically be passed through the pspec.
  83 class SimpleHandshakeRedir(SimpleHandshake):
  84     def __init__(self, mod, *args):
  85         print ("redir", mod, args)
  86         stage = self
  87         if args and args[0].stage:
  88             stage = args[0].stage
  89         SimpleHandshake.__init__(self, stage)
  90
  91
  92 class MaskCancellableRedir(MaskCancellable):
  93     def __init__(self, mod, *args):
  94         stage = self
  95         maskwid = args[0].maskwid
  96         if args[0].stage:
  97             stage = args[0].stage
  98         print ("redir mask", mod, args, maskwid)
  99         MaskCancellable.__init__(self, stage, maskwid)
 100