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     This work is funded through NLnet under Grant 2019-02-012
   7
   8 The reasons why this technique is being deployed is because SimpleHandshake
   9 needs to be dynamically replaced at the end-users' choice, without having
  10 to duplicate dozens of classes using multiple-inheritanc "Mix-in" techniques.
  11
  12 It is however extremely unusual, and has been explicitly limited to this *one*
  13 module.  DO NOT try to use this technique elsewhere, it is extremely hard to
  14 understand (meta-class programming).
  15
  16 """
  17
  18 from abc import ABCMeta
  19
  20 from nmutil.singlepipe import SimpleHandshake
  21 from nmutil.singlepipe import MaskCancellable
  22
  23 import threading
  24
  25 # with many thanks to jsbueno on stackexchange for this one
  26 # https://stackoverflow.com/questions/57273070/
  27 # list post:
  28 # http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-July/002259.html
  29
  30 class Meta(ABCMeta):
  31     registry = {}
  32     recursing = threading.local()
  33     recursing.check = False
  34     mlock = threading.Lock()
  35
  36     def __call__(cls, *args, **kw):
  37         mcls = cls.__class__
  38         if mcls.recursing.check:
  39             return super().__call__(*args, **kw)
  40         spec = args[0]
  41         base = spec.pipekls # pick up the dynamic class from PipelineSpec, HERE
  42
  43         if (cls, base) not in mcls.registry:
  44             print ("__call__", args, kw, cls, base,
  45                    base.__bases__, cls.__bases__)
  46             mcls.registry[cls, base] = type(
  47                 cls.__name__,
  48                 (cls, base) + cls.__bases__[1:],
  49                 {}
  50             )
  51         real_cls = mcls.registry[cls, base]
  52
  53         with mcls.mlock:
  54             mcls.recursing.check = True
  55             instance = real_cls.__class__.__call__(real_cls, *args, **kw)
  56             mcls.recursing.check = False
  57         return instance
  58
  59
  60 # Inherit from this class instead of SimpleHandshake (or other ControlBase
  61 # derivative), and the metaclass will instead *replace* DynamicPipe -
  62 # *at runtime* - with the class that is specified *as a parameter*
  63 # in PipelineSpec.
  64 #
  65 # as explained in the list posting and in the stackexchange post, this is
  66 # needed to avoid a MASSIVE suite of duplicated multiple-inheritance classes
  67 # that "Mix in" SimpleHandshake (or other).
  68 #
  69 # unfortunately, composition does not work in this instance
  70 # (make an *instance* of SimpleHandshake or other class and pass it in)
  71 # due to the multiple level inheritance, and in several places
  72 # the inheriting class needs to do some setup that the deriving class
  73 # needs in order to function correctly.
  74
  75 class DynamicPipe(metaclass=Meta):
  76     def __init__(self, *args):
  77         print ("DynamicPipe init", super(), args)
  78         super().__init__(self, *args)
  79
  80
  81 # bad hack: the DynamicPipe metaclass ends up creating an __init__ signature
  82 # for the dynamically-derived class.  luckily, SimpleHandshake only needs
  83 # "self" as the 1st argument (it is its own "Stage").  anything else
  84 # could hypothetically be passed through the pspec.
  85 class SimpleHandshakeRedir(SimpleHandshake):
  86     def __init__(self, mod, *args):
  87         print ("redir", mod, args)
  88         stage = self
  89         if args and args[0].stage:
  90             stage = args[0].stage
  91         SimpleHandshake.__init__(self, stage)
  92
  93
  94 class MaskCancellableRedir(MaskCancellable):
  95     def __init__(self, mod, *args):
  96         stage = self
  97         maskwid = args[0].maskwid
  98         if args[0].stage:
  99             stage = args[0].stage
 100         print ("redir mask", mod, args, maskwid)
 101         MaskCancellable.__init__(self, stage, maskwid)
 102