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lostmsuAlexCatarino
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Safe pointers (pythonnet#1043)
* NewReference type and an example usage * BorrowedReference + example, that exposes dangerous pattern * make BorrowedReference readonly ref struct * BorrowedReference.Pointer is a private readonly field * renamed NewReference.ToPyObject to MoveToPyObject * removed public property Pointer from NewReference and replaced with DangerousGetAddress
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+96
-9
lines changed

9 files changed

+96
-9
lines changed

‎src/runtime/BorrowedReference.cs‎

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@@ -0,0 +1,22 @@
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namespace Python.Runtime
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{
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using System;
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/// <summary>
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/// Represents a reference to a Python object, that is being lent, and
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/// can only be safely used until execution returns to the caller.
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/// </summary>
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readonly ref struct BorrowedReference
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{
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readonly IntPtr pointer;
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public bool IsNull => this.pointer == IntPtr.Zero;
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/// <summary>Gets a raw pointer to the Python object</summary>
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public IntPtr DangerousGetAddress()
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=> this.IsNull ? throw new NullReferenceException() : this.pointer;
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BorrowedReference(IntPtr pointer)
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{
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this.pointer = pointer;
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}
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}
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}

‎src/runtime/NewReference.cs‎

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@@ -0,0 +1,39 @@
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namespace Python.Runtime
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{
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using System;
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/// <summary>
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/// Represents a reference to a Python object, that is tracked by Python's reference counting.
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/// </summary>
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[NonCopyable]
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ref struct NewReference
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{
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IntPtr pointer;
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public bool IsNull => this.pointer == IntPtr.Zero;
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/// <summary>Gets a raw pointer to the Python object</summary>
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public IntPtr DangerousGetAddress()
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=> this.IsNull ? throw new NullReferenceException() : this.pointer;
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/// <summary>
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/// Returns <see cref="PyObject"/> wrapper around this reference, which now owns
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/// the pointer. Sets the original reference to <c>null</c>, as it no longer owns it.
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/// </summary>
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public PyObject MoveToPyObject()
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{
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if (this.IsNull) throw new NullReferenceException();
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var result = new PyObject(this.pointer);
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this.pointer = IntPtr.Zero;
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return result;
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}
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/// <summary>
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/// Removes this reference to a Python object, and sets it to <c>null</c>.
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/// </summary>
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public void Dispose()
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{
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if (!this.IsNull)
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Runtime.XDecref(this.pointer);
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this.pointer = IntPtr.Zero;
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}
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}
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}

‎src/runtime/NonCopyableAttribute.cs‎

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@@ -0,0 +1,6 @@
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namespace Python.Runtime
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{
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using System;
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[AttributeUsage(AttributeTargets.Struct)]
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class NonCopyableAttribute : Attribute { }
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}

‎src/runtime/Python.Runtime.15.csproj‎

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@@ -129,6 +129,13 @@
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<PackageReference Include="Microsoft.TargetingPack.NETFramework.v4.5" Version="1.0.1" ExcludeAssets="All" PrivateAssets="All" />
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</ItemGroup>
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<ItemGroup>
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<PackageReference Include="NonCopyableAnalyzer" Version="0.5.1">
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<PrivateAssets>all</PrivateAssets>
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<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
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</PackageReference>
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</ItemGroup>
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<Import Project="Sdk.targets" Sdk="Microsoft.NET.Sdk" />
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<PropertyGroup>

‎src/runtime/Python.Runtime.csproj‎

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@@ -85,6 +85,7 @@
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</Compile>
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<Compile Include="arrayobject.cs" />
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<Compile Include="assemblymanager.cs" />
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<Compile Include="BorrowedReference.cs" />
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<Compile Include="classderived.cs" />
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<Compile Include="classbase.cs" />
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<Compile Include="classmanager.cs" />
@@ -121,6 +122,8 @@
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<Compile Include="moduleobject.cs" />
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<Compile Include="modulepropertyobject.cs" />
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<Compile Include="nativecall.cs" />
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<Compile Include="NewReference.cs" />
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<Compile Include="NonCopyableAttribute.cs" />
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<Compile Include="overload.cs" />
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<Compile Include="propertyobject.cs" />
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<Compile Include="pyansistring.cs" />

‎src/runtime/assemblymanager.cs‎

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@@ -188,7 +188,7 @@ internal static void UpdatePath()
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pypath.Add("");
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for (var i = 0; i < count; i++)
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{
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IntPtr item = Runtime.PyList_GetItem(list, i);
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BorrowedReference item = Runtime.PyList_GetItem(list, i);
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string path = Runtime.GetManagedString(item);
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if (path != null)
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{

‎src/runtime/methodbinder.cs‎

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@@ -303,7 +303,7 @@ internal Binding Bind(IntPtr inst, IntPtr args, IntPtr kw, MethodBase info, Meth
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for (int i = 0; i < pynkwargs; ++i)
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{
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var keyStr = Runtime.GetManagedString(Runtime.PyList_GetItem(keylist, i));
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kwargDict[keyStr] = Runtime.PyList_GetItem(valueList, i);
306+
kwargDict[keyStr] = Runtime.PyList_GetItem(valueList, i).DangerousGetAddress();
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}
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Runtime.XDecref(keylist);

‎src/runtime/pydict.cs‎

Lines changed: 12 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -139,12 +139,20 @@ public PyObject Values()
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/// </remarks>
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public PyObject Items()
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{
142-
IntPtr items = Runtime.PyDict_Items(obj);
143-
if (items == IntPtr.Zero)
142+
var items = Runtime.PyDict_Items(this.obj);
143+
try
144144
{
145-
throw new PythonException();
145+
if (items.IsNull)
146+
{
147+
throw new PythonException();
148+
}
149+
150+
return items.MoveToPyObject();
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}
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finally
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{
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items.Dispose();
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}
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return new PyObject(items);
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}
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‎src/runtime/runtime.cs‎

Lines changed: 5 additions & 3 deletions
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@@ -1528,6 +1528,8 @@ internal static IntPtr PyUnicode_FromString(string s)
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return PyUnicode_FromUnicode(s, s.Length);
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}
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internal static string GetManagedString(in BorrowedReference borrowedReference)
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=> GetManagedString(borrowedReference.DangerousGetAddress());
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/// <summary>
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/// Function to access the internal PyUnicode/PyString object and
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/// convert it to a managed string with the correct encoding.
@@ -1610,7 +1612,7 @@ internal static bool PyDict_Check(IntPtr ob)
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internal static extern IntPtr PyDict_Values(IntPtr pointer);
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[DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
1613-
internal static extern IntPtr PyDict_Items(IntPtr pointer);
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internal static extern NewReference PyDict_Items(IntPtr pointer);
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[DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
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internal static extern IntPtr PyDict_Copy(IntPtr pointer);
@@ -1650,13 +1652,13 @@ internal static IntPtr PyList_New(long size)
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[DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
16511653
internal static extern IntPtr PyList_AsTuple(IntPtr pointer);
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1653-
internal static IntPtr PyList_GetItem(IntPtr pointer, long index)
1655+
internal static BorrowedReference PyList_GetItem(IntPtr pointer, long index)
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{
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return PyList_GetItem(pointer, new IntPtr(index));
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}
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16581660
[DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
1659-
private static extern IntPtr PyList_GetItem(IntPtr pointer, IntPtr index);
1661+
private static extern BorrowedReference PyList_GetItem(IntPtr pointer, IntPtr index);
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16611663
internal static int PyList_SetItem(IntPtr pointer, long index, IntPtr value)
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{

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