OpenColorIOTransformBinding : Add missing ScopedGILRelease

This was causing hangs when opening old Gaffer files in `1.3.x`, if the user's default layout was such that the Viewer would start a compute as soon as the file was opened. In this case, `acquireDefaultConfigPlug()` was still holding the GIL while creating the plug, and creating the plug would request cancellation of the compute, and the compute couldn't cancel if it was waiting for the GIL.

Changes.md

@@ -30,6 +30,7 @@ Fixes
 - Dispatch app : Removed unnecessary and misleading "Execute" button.
 - SceneAlgo : Fixed computation of `ScenePlug.object` in networks with nodes derived from `ObjectProcessor`. These include : `CameraTweaks`, `ClosestPointSampler`, `CollectPrimitiveVariables`, `CopyPrimitiveVariables`, `CurveSampler`, `DeleteCurves`, `DeleteFaces`, `DeletePoints`, `MapOffset`, `MapProjection`, `MeshDistortion`, `MeshNormals`, `MeshSegments`, `MeshTangents`, `MeshToPoints`, `MeshType`, `Orientation`, `PointsType`, `PrimitiveSampler`, `PrimitiveVariables`, `ReverseWinding`, `ShufflePrimitiveVariables` and `UVSampler` (#5406).
 - Metadata : Fixed redundant copying of metadata when promoting plugs.
+- OpenColorIO : Fixed hang when opening a script which didn't yet have the `openColorIO.config` plug.
 
 API
 ---

include/GafferImage/OpenColorIOConfigPlug.h

@@ -85,4 +85,6 @@ class GAFFERIMAGE_API OpenColorIOConfigPlug final : public Gaffer::ValuePlug
 		Gaffer::Signals::ScopedConnection m_plugSetConnection;
 };
 
+IE_CORE_DECLAREPTR( OpenColorIOConfigPlug );
+
 } // namespace GafferImage

src/GafferImageModule/OpenColorIOTransformBinding.cpp

@@ -71,6 +71,12 @@ boost::python::list supportedExtensions()
 	return result;
 }
 
+OpenColorIOConfigPlugPtr acquireDefaultConfigPlugWrapper( Gaffer::ScriptNode &scriptNode, bool createIfNecessary )
+{
+	IECorePython::ScopedGILRelease gilRelease;
+	return OpenColorIOConfigPlug::acquireDefaultConfigPlug( &scriptNode, createIfNecessary );
+}
+
 } // namespace
 
 void GafferImageModule::bindOpenColorIOTransform()
@@ -121,9 +127,8 @@ void GafferImageModule::bindOpenColorIOTransform()
 			)
 		)
 		.def(
-			"acquireDefaultConfigPlug", &OpenColorIOConfigPlug::acquireDefaultConfigPlug,
-			( arg( "scriptNode" ), arg( "createIfNecessary" ) = true ),
-			boost::python::return_value_policy<IECorePython::CastToIntrusivePtr>()
+			"acquireDefaultConfigPlug", &acquireDefaultConfigPlugWrapper,
+			( arg( "scriptNode" ), arg( "createIfNecessary" ) = true )
 		)
 		.staticmethod( "acquireDefaultConfigPlug" )
 	;