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Proposal: Safe pointers #1043

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Merged
filmor merged 9 commits into from
Feb 26, 2020
Merged

Proposal: Safe pointers #1043

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4a84a1e
NewReference type and an example usage
lostmsu Feb 13, 2020
88944a2
BorrowedReference + example, that exposes dangerous pattern
lostmsu Feb 13, 2020
e1ba92c
actually, borrowed refrences can be copied
lostmsu Feb 13, 2020
2d11f82
make BorrowedReference readonly ref struct
lostmsu Feb 13, 2020
dbb3dc5
updated old project file
lostmsu Feb 13, 2020
7304b25
BorrowedReference.Pointer is a private readonly field
lostmsu Feb 13, 2020
2bc218c
drop C# 8.0 requirement
lostmsu Feb 13, 2020
2cf9fc3
renamed NewReference.ToPyObject to MoveToPyObject
lostmsu Feb 23, 2020
6ae63cd
added xmldoc comments to *Reference members
lostmsu Feb 23, 2020
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renamed NewReference.ToPyObject to MoveToPyObject 
removed public property Pointer from NewReference and replaced with DangerousGetAddress
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@lostmsu
lostmsu committed Feb 23, 2020
commit 2cf9fc36872789bbbb863a173addb4b35b7c5e95
18 changes: 11 additions & 7 deletions src/runtime/NewReference.cs
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Expand Up @@ -4,23 +4,27 @@ namespace Python.Runtime
[NonCopyable]
ref struct NewReference
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@amos402 amos402 Feb 23, 2020

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Is it necessary to limit it as a stack-allocated value? If make it to a normal struct and rename it to PyReference, it can be assigned to a collection and implement the IDisposable for using () usage.
For better usage, a BorrowedReference may be able to promote to a PyReference for using the implict operate overloading.

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@lostmsu lostmsu Feb 23, 2020

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With [NoCopyable] you won't be able to put it into a collection anyway. And without [NoCopyable] it does not provide any safety guarantees.

Having it as ref struct saves you from adding ref everywhere you take it.

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@amos402 amos402 Feb 24, 2020

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But....sometimes I just want to put them into collections...😂

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@lostmsu lostmsu Feb 24, 2020

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Then you can still do DangerousGetHandle or create a PyObject from them.

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@amos402 amos402 Feb 24, 2020

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But this type also has a purpose for reminding others that it's a reference don't forget to decref it, isn't it?

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@lostmsu lostmsu Feb 24, 2020

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Because it must be clear from code, that care is necessary around this scenario.

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@lostmsu lostmsu Feb 24, 2020

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Also, as mentioned above, [NoCopyable] would already prevent you from putting an instance into a collection, even if ref were removed. And [NoCopyable] is basically the sole purpose of this change, as if you do

NewReference refA = GetNewReferenceSomehow();
NewReference refB = refA;

Then you already miappropriated refcounts.

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@amos402 amos402 Feb 24, 2020

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Maybe more introduce a type named PyHandle for that?

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@amos402 amos402 Feb 24, 2020

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emmm, but that make BorrowedReference embarrassed.

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@lostmsu lostmsu Feb 24, 2020

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@amos402 The idea with PyHandle can be reviewed separately. This PR is only for tracking new vs borrowed references as used in Python documentation for C API.

{
public IntPtr Pointer { get; set; }
public bool IsNull => this.Pointer == IntPtr.Zero;
IntPtr pointer;
public bool IsNull => this.pointer == IntPtr.Zero;

public PyObject ToPyObject()
/// <summary>Gets a raw pointer to the Python object</summary>
public IntPtr DangerousGetAddress()
=> this.IsNull ? throw new NullReferenceException() : this.pointer;

public PyObject MoveToPyObject()
{
if (this.IsNull) throw new NullReferenceException();

var result = new PyObject(this.Pointer);
this.Pointer = IntPtr.Zero;
var result = new PyObject(this.pointer);
this.pointer = IntPtr.Zero;
return result;
}

public void Dispose()
{
if (!this.IsNull)
Runtime.XDecref(this.Pointer);
this.Pointer = IntPtr.Zero;
Runtime.XDecref(this.pointer);
this.pointer = IntPtr.Zero;
}
}
}
2 changes: 1 addition & 1 deletion src/runtime/pydict.cs
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Expand Up @@ -147,7 +147,7 @@ public PyObject Items()
throw new PythonException();
}

return items.ToPyObject();
return items.MoveToPyObject();
}
finally
{
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