Break reference cycles in the edge triggers #727
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Rationale: * ClockCycles shares only one line of implementation with _Edge, and it's easier just to repeat it. * ClockCycles doesn't make much sense as a subclass of _Edge * _Edge is private anyway, so no consumer of the public API will care
eric-wieser
commented
Dec 16, 2018
| _RisingOrFallingEdge.__init__(self, signal, rising=False) | ||
|
|
||
| class Edge(_EdgeBase): | ||
| """ Triggers on either edge in a signal """ |
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As a bonus, this now gives these names docstrings, where previously help(cocotb.triggers.FallingEdge) would give nothing
Previously there was a cyclic reference between `Signal._r_edge -> _Edge.signal -> ...` This takes the same approach as 94eeaba, using a weak dictionary to ensure edges keep their signal alive, but not vice versa.
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Thanks @imphil for the fast approval! |
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Dec 20, 2018
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
We need to override class-construction without allowing `__init__` to run a second time.
One option would be to just remove `__init__` entirely, and move the contents into `__new__`.
The other option, which I take in this patch, is to introduce a metaclass overriding the `__call__` operator on class types.
I'm not convinced this is the best approach, but it does fix the problem.
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Dec 20, 2018
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
We need to override class-construction without allowing `__init__` to run a second time.
This introduces a simple metaclass to allow overriding the behavior of `RisingEdge.__call__(...)`
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 7, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
We need to override class-construction without allowing `__init__` to run a second time.
This introduces a simple metaclass to allow overriding the behavior of `RisingEdge.__call__(...)`
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 7, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
We need to override class-construction without allowing `__init__` to run a second time.
One option would be to just remove `__init__` entirely, and move the contents into `__new__`.
The other option, which I take in this patch, is to introduce a metaclass overriding the `__call__` operator on class types.
I'm not convinced this is the best approach, but it does fix the problem.
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 7, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
We need to override class-construction without allowing `__init__` to run a second time.
This introduces a simple metaclass to allow overriding the behavior of `RisingEdge.__call__(...)`
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 7, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
B = SomeClass(1)
```
We need to override class-construction without allowing `__init__` to run a second time.
One option would be to just remove `__init__` entirely, and move the contents into `__new__`.
The other option, which I take in this patch, is to introduce a metaclass overriding the `__call__` operator on class types.
I'm not convinced this is the best approach, but it does fix the problem.
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 7, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
For the sake of simplicity, this commit undoes the merger between the factory functions and the classes themselves, while keeping the weakref behavior.
In future, it would be good to explore the more complex approach taken in cocotbgh-733, which ensures that `isinstance(Join(), Join)`, which this patch does not.
Since this property was not true before cocotbgh-723 and cocotbgh-727 anyway, we can afford to revert that improvement in order to get a release out the door.
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 8, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
For the sake of simplicity, this commit undoes the merger between the factory functions and the classes themselves, while keeping the weakref behavior.
In future, it would be good to explore the more complex approach taken in cocotbgh-733, which ensures that `isinstance(Join(), Join)`, which this patch does not.
Since this property was not true before cocotbgh-723 and cocotbgh-727 anyway, we can afford to revert that improvement in order to get a release out the door.
eric-wieser
added a commit
to eric-wieser/cocotb
that referenced
this pull request
Jan 8, 2019
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A
# A.__init__(1)
B = SomeClass(1)
# SomeClass.__new__(SomeClass, 1) -> A # reusing the existing instance
# A.__init__(1) # uh oh, we reset A.state
```
For the sake of simplicity, this commit undoes the merger between the factory functions and the classes themselves, while keeping the weakref behavior.
In future, it would be good to explore the more complex approach taken in cocotbgh-733, which ensures that `isinstance(Join(), Join)`, which this patch does not.
Since this property was not true before cocotbgh-723 and cocotbgh-727 anyway, we can afford to revert that improvement in order to get a release out the door.
ktbarrett
pushed a commit
to ktbarrett/cocotb
that referenced
this pull request
Mar 6, 2020
Break reference cycles in the edge triggers
ktbarrett
pushed a commit
to ktbarrett/cocotb
that referenced
this pull request
Mar 6, 2020
…by a misunderstanding of how __new__ works
In those patches, I declared classes that were roughly
```python
class SomeClass:
def __new__(cls, arg):
try:
return existing[arg]
except KeyError:
return super(SomeClass, cls).__new__(cls, arg)
def __init__(self, arg):
self.arg = arg
self.state = 0
```
This approach has a fatal flaw (cocotbgh-729), with function calls shown in the following code:
```python
A = SomeClass(1)
B = SomeClass(1)
```
We need to override class-construction without allowing `__init__` to run a second time.
One option would be to just remove `__init__` entirely, and move the contents into `__new__`.
The other option, which I take in this patch, is to introduce a metaclass overriding the `__call__` operator on class types.
I'm not convinced this is the best approach, but it does fix the problem.
ktbarrett
pushed a commit
to ktbarrett/cocotb
that referenced
this pull request
Mar 6, 2020
Fix a regression introduced in cocotbgh-727 and cocotbgh-723, caused by a misunderstanding of how __new__ works
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Noticed in the comments of #723.