[libcamera-devel] [PATCH 5/5] py: Move to mainline pybind11 version
Tomi Valkeinen
tomi.valkeinen at ideasonboard.com
Tue May 30 13:34:17 CEST 2023
On 30/05/2023 14:29, Laurent Pinchart wrote:
> Hi Tomi,
>
> On Tue, May 30, 2023 at 02:16:23PM +0300, Tomi Valkeinen wrote:
>> On 30/05/2023 13:12, Laurent Pinchart wrote:
>>> 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.
>
> I think the package is called python-pybind in buildroot.
>
>> 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.
>
> Could you test with the buildroot python-pybind package ? If that works,
> is there any blocker to dropping the subproject ?
I will try with the latest buildroot. The python-pybind didn't work when
I tried it the some time ago. The issues were the familiar "what belongs
to the host and what belongs to the target and how does the host get the
python details about the target".
> I don't mind dropping the subproject in a separate patch, to make it
> easy to revert it.
>
>>>> 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.
>
> That's lots of magic :-)
Indeed. I think the main thing/feature with pybind11 is the handling of
the memory between Python and C++. It's complex...
Tomi
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