[libcamera-devel] [PATCH 5/5] py: Move to mainline pybind11 version
Tomi Valkeinen
tomi.valkeinen at ideasonboard.com
Tue May 30 13:16:23 CEST 2023
On 30/05/2023 13:12, Laurent Pinchart wrote:
> Hi Tomi,
>
> Thank you for the patch.
>
> On Tue, May 30, 2023 at 12:20:16PM +0300, Tomi Valkeinen wrote:
>> We are using pybind11 'smart_holder' branch to solve the Camera
>> destructor issue (see the comment in this patch, or the commit
>> that originally added Python bindings support).
>>
>> As it would be very nice to use the mainline pybind11 (which is packaged
>> in distributions), this patch adds a workaround allowing us to move to
>> the mainline pybind11 version.
>>
>> The workaround is simply creating a custom holder class, used only for
>> the Camera, which wraps around the shared_ptr. This makes the compiler
>> happy.
>>
>> Moving to mainline pybdin11 is achieved with:
>
> s/pybdin11/pybind11/
>
>>
>> - Change the pybind11 wrap to point to the mainline pybdind11 version
>>
>> - Change the meson.build file to use a system-installed pybind11 if
>> available, and use the pybind11 subproject as a fallback. The fallback
>> is there as a convenience, as pybind11 may not be available in
>> pre-packaged form in all environments.
>
> Given that Python bindings isn't a core feature of libcamera, do we
> really need a subproject, or could we disable the Python bindings when
> pybind11 isn't found ? We have subprojects for libyaml and libyuv, as
> they're required by the libcamera core and the Android camera HAL and
> not available on AOSP, but for optional features, I would prefer relying
> on the build environment to provide the necessary dependencies,
> especially given that both Debian and Fedora have a pybind11 package.
Well... It's for my convenience, at least =). Buildroot doesn't/didn't
have a properly working pybind11.
Maybe we can drop it, but I'd rather do it later so that we don't mess
up too many things at the same time.
Or I can just add a patch to my local tree which adds the subproject, if
the consensus is to drop it from libcamera.
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
>> ---
>> src/py/libcamera/meson.build | 11 ++--
>> src/py/libcamera/py_camera_manager.h | 2 +-
>> src/py/libcamera/py_color_space.cpp | 2 +-
>> src/py/libcamera/py_controls_generated.cpp.in | 2 +-
>> src/py/libcamera/py_enums.cpp | 2 +-
>> src/py/libcamera/py_formats_generated.cpp.in | 2 +-
>> src/py/libcamera/py_geometry.cpp | 2 +-
>> src/py/libcamera/py_helpers.h | 2 +-
>> src/py/libcamera/py_main.cpp | 52 +++++++++++++++++--
>> .../libcamera/py_properties_generated.cpp.in | 2 +-
>> src/py/libcamera/py_transform.cpp | 2 +-
>> subprojects/.gitignore | 2 +-
>> subprojects/pybind11.wrap | 18 ++++---
>> 13 files changed, 76 insertions(+), 25 deletions(-)
>>
>> diff --git a/src/py/libcamera/meson.build b/src/py/libcamera/meson.build
>> index f87b1b4d..9d86d8bf 100644
>> --- a/src/py/libcamera/meson.build
>> +++ b/src/py/libcamera/meson.build
>> @@ -7,10 +7,15 @@ if not py3_dep.found()
>> subdir_done()
>> endif
>>
>> -pycamera_enabled = true
>> +pybind11_dep = dependency('pybind11', required : get_option('pycamera'),
>> + fallback : ['pybind11', 'pybind11_dep'])
>> +
>> +if not pybind11_dep.found()
>> + pycamera_enabled = false
>> + subdir_done()
>> +endif
>>
>> -pybind11_proj = subproject('pybind11')
>> -pybind11_dep = pybind11_proj.get_variable('pybind11_dep')
>> +pycamera_enabled = true
>>
>> pycamera_sources = files([
>> 'py_camera_manager.cpp',
>> diff --git a/src/py/libcamera/py_camera_manager.h b/src/py/libcamera/py_camera_manager.h
>> index 3525057d..3574db23 100644
>> --- a/src/py/libcamera/py_camera_manager.h
>> +++ b/src/py/libcamera/py_camera_manager.h
>> @@ -9,7 +9,7 @@
>>
>> #include <libcamera/libcamera.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> using namespace libcamera;
>>
>> diff --git a/src/py/libcamera/py_color_space.cpp b/src/py/libcamera/py_color_space.cpp
>> index a8301e3d..5201121a 100644
>> --- a/src/py/libcamera/py_color_space.cpp
>> +++ b/src/py/libcamera/py_color_space.cpp
>> @@ -9,7 +9,7 @@
>> #include <libcamera/libcamera.h>
>>
>> #include <pybind11/operators.h>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>> #include <pybind11/stl.h>
>>
>> namespace py = pybind11;
>> diff --git a/src/py/libcamera/py_controls_generated.cpp.in b/src/py/libcamera/py_controls_generated.cpp.in
>> index cb8442ba..18fa57d9 100644
>> --- a/src/py/libcamera/py_controls_generated.cpp.in
>> +++ b/src/py/libcamera/py_controls_generated.cpp.in
>> @@ -9,7 +9,7 @@
>>
>> #include <libcamera/control_ids.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> namespace py = pybind11;
>>
>> diff --git a/src/py/libcamera/py_enums.cpp b/src/py/libcamera/py_enums.cpp
>> index 96d4beef..803c4e7e 100644
>> --- a/src/py/libcamera/py_enums.cpp
>> +++ b/src/py/libcamera/py_enums.cpp
>> @@ -7,7 +7,7 @@
>>
>> #include <libcamera/libcamera.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> namespace py = pybind11;
>>
>> diff --git a/src/py/libcamera/py_formats_generated.cpp.in b/src/py/libcamera/py_formats_generated.cpp.in
>> index b88807f3..a3f7f94d 100644
>> --- a/src/py/libcamera/py_formats_generated.cpp.in
>> +++ b/src/py/libcamera/py_formats_generated.cpp.in
>> @@ -9,7 +9,7 @@
>>
>> #include <libcamera/formats.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> namespace py = pybind11;
>>
>> diff --git a/src/py/libcamera/py_geometry.cpp b/src/py/libcamera/py_geometry.cpp
>> index 84b0cb08..5c2aeac4 100644
>> --- a/src/py/libcamera/py_geometry.cpp
>> +++ b/src/py/libcamera/py_geometry.cpp
>> @@ -11,7 +11,7 @@
>> #include <libcamera/libcamera.h>
>>
>> #include <pybind11/operators.h>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>> #include <pybind11/stl.h>
>>
>> namespace py = pybind11;
>> diff --git a/src/py/libcamera/py_helpers.h b/src/py/libcamera/py_helpers.h
>> index cd31e2cc..983969df 100644
>> --- a/src/py/libcamera/py_helpers.h
>> +++ b/src/py/libcamera/py_helpers.h
>> @@ -7,7 +7,7 @@
>>
>> #include <libcamera/libcamera.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> pybind11::object controlValueToPy(const libcamera::ControlValue &cv);
>> libcamera::ControlValue pyToControlValue(const pybind11::object &ob, libcamera::ControlType type);
>> diff --git a/src/py/libcamera/py_main.cpp b/src/py/libcamera/py_main.cpp
>> index c66b90cd..bbae7a99 100644
>> --- a/src/py/libcamera/py_main.cpp
>> +++ b/src/py/libcamera/py_main.cpp
>> @@ -17,7 +17,7 @@
>> #include <libcamera/libcamera.h>
>>
>> #include <pybind11/functional.h>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>> #include <pybind11/stl.h>
>> #include <pybind11/stl_bind.h>
>>
>> @@ -33,6 +33,50 @@ namespace libcamera {
>> LOG_DEFINE_CATEGORY(Python)
>>
>> }
>
> Missing blank line.
>
>> +/*
>> + * This is a holder class used only for the Camera class, for the sole purpose
>> + * of avoiding the compilation issue with Camera's private destructor.
>> + *
>> + * pybind11 requires a public destructor for classes held with shared_ptrs, even
>> + * in cases where the public destructor is not strictly needed. The current
>> + * understanding is that there are the following options to solve the problem:
>> + *
>> + * - Use pybind11 'smart_holder' branch. The downside is that 'smart_holder'
>> + * is not the mainline branch, and not available in distributions.
>> + * - https://github.com/pybind/pybind11/pull/2067
>> + * - Make the Camera destructor public
>> + * - Something like the PyCameraSmartPtr here, which adds a layer, hiding the
>> + * issue.
>> + */
>> +template<typename T>
>> +class PyCameraSmartPtr
>> +{
>> +public:
>> + using element_type = T;
>> +
>> + PyCameraSmartPtr()
>> + {
>> + }
>> +
>> + explicit PyCameraSmartPtr(T *)
>> + {
>> + throw std::runtime_error("invalid SmartPtr constructor call");
>> + }
>> +
>> + explicit PyCameraSmartPtr(std::shared_ptr<T> p)
>> + : ptr_(p)
>> + {
>> + }
>> +
>> + T *get() const { return ptr_.get(); }
>> +
>> + operator std::shared_ptr<T>() const { return ptr_; }
>> +
>> +private:
>> + std::shared_ptr<T> ptr_;
>> +};
>> +
>> +PYBIND11_DECLARE_HOLDER_TYPE(T, PyCameraSmartPtr<T>);
>>
>> /*
>> * Note: global C++ destructors can be ran on this before the py module is
>> @@ -65,8 +109,8 @@ PYBIND11_MODULE(_libcamera, m)
>> * https://pybind11.readthedocs.io/en/latest/advanced/misc.html#avoiding-c-types-in-docstrings
>> */
>>
>> - auto pyCameraManager = py::class_<PyCameraManager>(m, "CameraManager");
>> - auto pyCamera = py::class_<Camera>(m, "Camera");
>> + auto pyCameraManager = py::class_<PyCameraManager, std::shared_ptr<PyCameraManager>>(m, "CameraManager");
>
> Why does PyCameraManager need to be changed ?
The default holder is unique_ptr. We handle the camera manager with the
singleton pattern, using shared_ptr. So we always want to use shared_ptr.
If we don't do this, the camera manager gets freed during operation,
leading to a crash.
I have to say the exact details escape me, but the smart_holder version
handles this smartly, as we do return a shared_ptr from the singleton()
function. But the mainline version doesn't cope with that, and I believe
it converts the shared_ptr to a unique_ptr, unless we specifically tell
it to use the shared_ptr as a holder class.
I'll add a note about this to the commit message.
>> + auto pyCamera = py::class_<Camera, PyCameraSmartPtr<Camera>>(m, "Camera");
>> auto pyCameraConfiguration = py::class_<CameraConfiguration>(m, "CameraConfiguration");
>> auto pyCameraConfigurationStatus = py::enum_<CameraConfiguration::Status>(pyCameraConfiguration, "Status");
>> auto pyStreamConfiguration = py::class_<StreamConfiguration>(m, "StreamConfiguration");
>> @@ -271,7 +315,7 @@ PYBIND11_MODULE(_libcamera, m)
>> .def("range", &StreamFormats::range);
>>
>> pyFrameBufferAllocator
>> - .def(py::init<std::shared_ptr<Camera>>(), py::keep_alive<1, 2>())
>> + .def(py::init<PyCameraSmartPtr<Camera>>(), py::keep_alive<1, 2>())
>> .def("allocate", [](FrameBufferAllocator &self, Stream *stream) {
>> int ret = self.allocate(stream);
>> if (ret < 0)
>> diff --git a/src/py/libcamera/py_properties_generated.cpp.in b/src/py/libcamera/py_properties_generated.cpp.in
>> index 044b2b2a..e49b6e91 100644
>> --- a/src/py/libcamera/py_properties_generated.cpp.in
>> +++ b/src/py/libcamera/py_properties_generated.cpp.in
>> @@ -9,7 +9,7 @@
>>
>> #include <libcamera/property_ids.h>
>>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>>
>> namespace py = pybind11;
>>
>> diff --git a/src/py/libcamera/py_transform.cpp b/src/py/libcamera/py_transform.cpp
>> index 08783e29..f3a0bfaf 100644
>> --- a/src/py/libcamera/py_transform.cpp
>> +++ b/src/py/libcamera/py_transform.cpp
>> @@ -9,7 +9,7 @@
>> #include <libcamera/libcamera.h>
>>
>> #include <pybind11/operators.h>
>> -#include <pybind11/smart_holder.h>
>> +#include <pybind11/pybind11.h>
>> #include <pybind11/stl.h>
>>
>> namespace py = pybind11;
>> diff --git a/subprojects/.gitignore b/subprojects/.gitignore
>> index 0a8fd3a6..ebe59479 100644
>> --- a/subprojects/.gitignore
>> +++ b/subprojects/.gitignore
>> @@ -4,4 +4,4 @@
>> /libyaml
>> /libyuv
>> /packagecache
>> -/pybind11
>> +/pybind11-*
>> diff --git a/subprojects/pybind11.wrap b/subprojects/pybind11.wrap
>> index dd02687b..96ec57a1 100644
>> --- a/subprojects/pybind11.wrap
>> +++ b/subprojects/pybind11.wrap
>> @@ -1,11 +1,13 @@
>> -# SPDX-License-Identifier: CC0-1.0
>> -
>
> Please specify a license.
Hmm, I wonder what it is... This file is downloaded with the "meson wrap
install" tool. https://github.com/mesonbuild/wrapdb says "MIT", so
perhaps it's that. I hope it won't get overwritten every time we update
the wrap with "meson wrap update"...
Tomi
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