[libcamera-devel] [PATCH 04/10] libcamera: device_enumerator: Reference-count MediaDevice instances
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Fri Jan 25 00:55:08 CET 2019
Hi Jacopo,
On Fri, Jan 25, 2019 at 12:16:41AM +0100, Jacopo Mondi wrote:
> On Thu, Jan 24, 2019 at 12:16:45PM +0200, Laurent Pinchart wrote:
> > The MediaDevice class will be the entry point to hot-unplug, as it
> > corresponds to the kernel devices that will report device removal
> > events. The class will signal media device disconnection to pipeline
> > handlers, which will clean up resources as a result.
> >
> > This can't be performed synchronously as references may exist to the
> > related Camera objects in applications. The MediaDevice object thus
> > needs to be reference-counted in order to support unplugging, as
> > otherwise pipeline handlers would be required to drop all the references
> > to the media device they have borrowed synchronously with the
> > disconnection signal handler, which would be very error prone (if even
> > possible at all in a sane way).
> >
> > Handle MedieDevice instances with std::shared_ptr<> to support this.
> >
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> > src/libcamera/device_enumerator.cpp | 23 ++++++++++----------
> > src/libcamera/include/device_enumerator.h | 4 ++--
> > src/libcamera/pipeline/ipu3/ipu3.cpp | 11 ++++------
> > src/libcamera/pipeline/uvcvideo.cpp | 4 ++--
> > src/libcamera/pipeline/vimc.cpp | 4 ++--
> > test/media_device/media_device_link_test.cpp | 2 +-
> > test/pipeline/ipu3/ipu3_pipeline_test.cpp | 2 +-
> > 7 files changed, 23 insertions(+), 27 deletions(-)
> >
> > diff --git a/src/libcamera/device_enumerator.cpp b/src/libcamera/device_enumerator.cpp
> > index 8100972a8d04..149ffbf9aea6 100644
> > --- a/src/libcamera/device_enumerator.cpp
> > +++ b/src/libcamera/device_enumerator.cpp
> > @@ -166,12 +166,10 @@ std::unique_ptr<DeviceEnumerator> DeviceEnumerator::create()
> >
> > DeviceEnumerator::~DeviceEnumerator()
> > {
> > - for (MediaDevice *dev : devices_) {
> > - if (dev->busy())
> > + for (std::shared_ptr<MediaDevice> media : devices_) {
> > + if (media->busy())
>
> Not sure I got this. The assignement to media in the range-based for
> loop creates a copy, right? Does the device enumerator need to drop
> that? They are added to a vector of shared_ptr with
>
> devices_.push_back(std::move(media));
>
> So I'm expecting this to happen. What have I missed?
It helps to look at how range-based for loops are implemented. The C++
standard explains they are equivalent to the following code.
{
auto && __range = range_expression ;
for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin) {
range_declaration = *__begin;
loop_statement
}
}
which, when applied to our code, produces
1. {
2. auto && __range = devices_;
3. for (auto __begin = begin(__range), __end = end(__range); __begin != __end; ++__begin) {
4. std::shared_ptr<MediaDevice> media = *__begin;
5. if (media->busy())
6. LOG(DeviceEnumerator, Error)
7. << "Removing media device while still in use";
8. }
9. }
On line 2 a reference to devices_ is created (as an rvalue reference as
range_expression could be the return of a function, in which case using
an lvalue would generate an lvalue reference to temporary object error).
__range thus references devices_, it doesn't create a copy of the
vector.
On line 3 we use a classic iterator-based loop, with __begin taking the
type std::vector<std::shared_ptr<MediaDevice>>::iterator.
On line 4 the media object is created as a copy of the vector entry
being iterated on. This creates a new std::shared_ptr<> instance,
incrementing the reference count.
On line 8 the media object gets out of scope, and is thus destroyed. The
reference count is decremented.
The for loop thus doesn't modify the reference count on the objects.
At the end of the destructor all the member variables are destroyed.
Destroying devices_ will call the destructor of each entry in turn, and
then destroy the vector itself. The references we added to devices_ in
DeviceEnumerator::addDevice() are thus dropped at this point, and
everything is fine. There is thus no need to destroy the devices_
entries manually. The "delete dev" statement was need because the
devices_ vector contained pointers to MediaDevice objects that it owned,
so they had to be deleted.
> > LOG(DeviceEnumerator, Error)
> > << "Removing media device while still in use";
> > -
> > - delete dev;
> > }
> > }
> >
> > @@ -211,7 +209,7 @@ DeviceEnumerator::~DeviceEnumerator()
> > */
> > int DeviceEnumerator::addDevice(const std::string &deviceNode)
> > {
> > - MediaDevice *media = new MediaDevice(deviceNode);
> > + std::shared_ptr<MediaDevice> media = std::make_shared<MediaDevice>(deviceNode);
> >
> > int ret = media->open();
> > if (ret < 0)
> > @@ -243,9 +241,10 @@ int DeviceEnumerator::addDevice(const std::string &deviceNode)
> > return ret;
> > }
> >
> > - devices_.push_back(media);
> > media->close();
> >
> > + devices_.push_back(std::move(media));
> > +
> > return 0;
> > }
> >
> > @@ -260,17 +259,17 @@ int DeviceEnumerator::addDevice(const std::string &deviceNode)
> > *
> > * \return pointer to the matching MediaDevice, or nullptr if no match is found
> > */
> > -MediaDevice *DeviceEnumerator::search(const DeviceMatch &dm)
> > +std::shared_ptr<MediaDevice> DeviceEnumerator::search(const DeviceMatch &dm)
> > {
> > - for (MediaDevice *dev : devices_) {
> > - if (dev->busy())
> > + for (std::shared_ptr<MediaDevice> media : devices_) {
> > + if (media->busy())
> > continue;
> >
> > - if (dm.match(dev)) {
> > + if (dm.match(media.get())) {
> > LOG(DeviceEnumerator, Debug)
> > << "Successful match for media device \""
> > - << dev->driver() << "\"";
> > - return dev;
> > + << media->driver() << "\"";
> > + return std::move(media);
> > }
> > }
> >
> > diff --git a/src/libcamera/include/device_enumerator.h b/src/libcamera/include/device_enumerator.h
> > index 40c7750b49fc..3f87a6255303 100644
> > --- a/src/libcamera/include/device_enumerator.h
> > +++ b/src/libcamera/include/device_enumerator.h
> > @@ -42,13 +42,13 @@ public:
> > virtual int init() = 0;
> > virtual int enumerate() = 0;
> >
> > - MediaDevice *search(const DeviceMatch &dm);
> > + std::shared_ptr<MediaDevice> search(const DeviceMatch &dm);
> >
> > protected:
> > int addDevice(const std::string &deviceNode);
> >
> > private:
> > - std::vector<MediaDevice *> devices_;
> > + std::vector<std::shared_ptr<MediaDevice>> devices_;
> >
> > virtual std::string lookupDeviceNode(int major, int minor) = 0;
> > };
> > diff --git a/src/libcamera/pipeline/ipu3/ipu3.cpp b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > index 13ff7da4c99e..9831f74fe53f 100644
> > --- a/src/libcamera/pipeline/ipu3/ipu3.cpp
> > +++ b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > @@ -29,8 +29,8 @@ public:
> > bool match(DeviceEnumerator *enumerator);
> >
> > private:
> > - MediaDevice *cio2_;
> > - MediaDevice *imgu_;
> > + std::shared_ptr<MediaDevice> cio2_;
> > + std::shared_ptr<MediaDevice> imgu_;
> >
> > void registerCameras();
> > };
> > @@ -47,9 +47,6 @@ PipelineHandlerIPU3::~PipelineHandlerIPU3()
> >
> > if (imgu_)
> > imgu_->release();
> > -
> > - cio2_ = nullptr;
> > - imgu_ = nullptr;
> > }
> >
> > bool PipelineHandlerIPU3::match(DeviceEnumerator *enumerator)
> > @@ -78,11 +75,11 @@ bool PipelineHandlerIPU3::match(DeviceEnumerator *enumerator)
> > imgu_dm.add("ipu3-imgu 1 viewfinder");
> > imgu_dm.add("ipu3-imgu 1 3a stat");
> >
> > - cio2_ = enumerator->search(cio2_dm);
> > + cio2_ = std::move(enumerator->search(cio2_dm));
> > if (!cio2_)
> > return false;
> >
> > - imgu_ = enumerator->search(imgu_dm);
> > + imgu_ = std::move(enumerator->search(imgu_dm));
> > if (!imgu_)
> > return false;
> >
> > diff --git a/src/libcamera/pipeline/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo.cpp
> > index 3ebc074093ab..73bad6714bb4 100644
> > --- a/src/libcamera/pipeline/uvcvideo.cpp
> > +++ b/src/libcamera/pipeline/uvcvideo.cpp
> > @@ -23,7 +23,7 @@ public:
> > bool match(DeviceEnumerator *enumerator);
> >
> > private:
> > - MediaDevice *dev_;
> > + std::shared_ptr<MediaDevice> dev_;
> > };
> >
> > PipelineHandlerUVC::PipelineHandlerUVC(CameraManager *manager)
> > @@ -41,7 +41,7 @@ bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
> > {
> > DeviceMatch dm("uvcvideo");
> >
> > - dev_ = enumerator->search(dm);
> > + dev_ = std::move(enumerator->search(dm));
> >
> > if (!dev_)
> > return false;
> > diff --git a/src/libcamera/pipeline/vimc.cpp b/src/libcamera/pipeline/vimc.cpp
> > index 68bfe9b12ab6..521b20d3a120 100644
> > --- a/src/libcamera/pipeline/vimc.cpp
> > +++ b/src/libcamera/pipeline/vimc.cpp
> > @@ -23,7 +23,7 @@ public:
> > bool match(DeviceEnumerator *enumerator);
> >
> > private:
> > - MediaDevice *dev_;
> > + std::shared_ptr<MediaDevice> dev_;
> > };
> >
> > PipeHandlerVimc::PipeHandlerVimc(CameraManager *manager)
> > @@ -51,7 +51,7 @@ bool PipeHandlerVimc::match(DeviceEnumerator *enumerator)
> > dm.add("RGB/YUV Input");
> > dm.add("Scaler");
> >
> > - dev_ = enumerator->search(dm);
> > + dev_ = std::move(enumerator->search(dm));
> > if (!dev_)
> > return false;
> >
> > diff --git a/test/media_device/media_device_link_test.cpp b/test/media_device/media_device_link_test.cpp
> > index ac5b632f8ed1..58a55cdfee63 100644
> > --- a/test/media_device/media_device_link_test.cpp
> > +++ b/test/media_device/media_device_link_test.cpp
> > @@ -240,7 +240,7 @@ class MediaDeviceLinkTest : public Test
> >
> > private:
> > unique_ptr<DeviceEnumerator> enumerator;
> > - MediaDevice *dev_;
> > + shared_ptr<MediaDevice> dev_;
> > };
> >
> > TEST_REGISTER(MediaDeviceLinkTest);
> > diff --git a/test/pipeline/ipu3/ipu3_pipeline_test.cpp b/test/pipeline/ipu3/ipu3_pipeline_test.cpp
> > index 482c12499a86..953f0233cde4 100644
> > --- a/test/pipeline/ipu3/ipu3_pipeline_test.cpp
> > +++ b/test/pipeline/ipu3/ipu3_pipeline_test.cpp
> > @@ -65,7 +65,7 @@ int IPU3PipelineTest::init()
> > return TestSkip;
> > }
> >
> > - MediaDevice *cio2 = enumerator->search(cio2_dm);
> > + std::shared_ptr<MediaDevice> cio2 = enumerator->search(cio2_dm);
> > if (!cio2) {
> > cerr << "Failed to find IPU3 CIO2: test skip" << endl;
> > return TestSkip;
--
Regards,
Laurent Pinchart
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