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libcamera: camera: Use invokeMethod() for pipe_->acquire() and pipe_->release()

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The uvcvideo driver needs to open / close its /dev/video# node from
pipe_->acquireDevices() / pipe_->releaseDevices().

V4L2VideoDevice::open() creates an EventNotifier and this notifier needs
to be created from the CameraManager thread.

Use invokeMethod() for pipe_->acquire() and pipe_->release() so that the
EventNotifiers are created from the CameraManager thread context.

Running pipe_->acquire() and pipe_->release() from the CameraManager
thread context serializes all calls to them. Drop PipelineHandler::lock_
this now is no longer necessary and update the "\context" part of the
documentation for acquire[Device]() and release[Device]() to match.

Note the delayed opening of /dev/video# is a special case because the
kernel uvcvideo driver powers on the USB device as soon as /dev/video#
is opened. This behavior should *not* be copied by other pipeline
handlers.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
This commit is contained in:
Hans de Goede 2024-08-30 13:12:06 +02:00 • committed by Laurent Pinchart
parent c05e45ac77
commit 11e396bf9f
3 changed files with 11 additions and 12 deletions
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5
include/libcamera/internal/pipeline_handler.h
View file

@ -14,7 +14,6 @@
#include <sys/types.h>
#include <vector>
#include <libcamera/base/mutex.h>
#include <libcamera/base/object.h>
#include <libcamera/controls.h>
@ -99,9 +98,7 @@ private:
std::queue<Request *> waitingRequests_;
const char *name_;
Mutex lock_;
unsigned int useCount_ LIBCAMERA_TSA_GUARDED_BY(lock_);
unsigned int useCount_;
friend class PipelineHandlerFactoryBase;
};

6
src/libcamera/camera.cpp
View file

@ -995,7 +995,8 @@ int Camera::acquire()
if (ret < 0)
return ret == -EACCES ? -EBUSY : ret;
if (!d->pipe_->acquire(this)) {
if (!d->pipe_->invokeMethod(&PipelineHandler::acquire,
ConnectionTypeBlocking, this)) {
LOG(Camera, Info)
<< "Pipeline handler in use by another process";
return -EBUSY;
@ -1030,7 +1031,8 @@ int Camera::release()
return ret == -EACCES ? -EBUSY : ret;
if (d->isAcquired())
d->pipe_->release(this);
d->pipe_->invokeMethod(&PipelineHandler::release,
ConnectionTypeBlocking, this);
d->setState(Private::CameraAvailable);

12
src/libcamera/pipeline_handler.cpp
View file

@ -157,7 +157,7 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
* Pipeline handlers shall not call this function directly as the Camera class
* handles access internally.
*
* \context This function is \threadsafe.
* \context This function is called from the CameraManager thread.
*
* \return True if the pipeline handler was acquired, false if another process
* has already acquired it
@ -165,8 +165,6 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
*/
bool PipelineHandler::acquire(Camera *camera)
{
MutexLocker locker(lock_);
if (useCount_ == 0) {
for (std::shared_ptr<MediaDevice> &media : mediaDevices_) {
if (!media->lock()) {
@ -199,14 +197,12 @@ bool PipelineHandler::acquire(Camera *camera)
* Pipeline handlers shall not call this function directly as the Camera class
* handles access internally.
*
* \context This function is \threadsafe.
* \context This function is called from the CameraManager thread.
*
* \sa acquire()
*/
void PipelineHandler::release(Camera *camera)
{
MutexLocker locker(lock_);
ASSERT(useCount_);
releaseDevice(camera);
@ -230,6 +226,8 @@ void PipelineHandler::release(Camera *camera)
* powers on the USB device as soon as /dev/video# is opened. This behavior
* should *not* be copied by other pipeline handlers.
*
* \context This function is called from the CameraManager thread.
*
* \return True on success, false on failure
* \sa releaseDevice()
*/
@ -250,6 +248,8 @@ bool PipelineHandler::acquireDevice([[maybe_unused]] Camera *camera)
* release them until releaseDevice() has been called for all previously
* acquired cameras.
*
* \context This function is called from the CameraManager thread.
*
* \sa acquireDevice()
*/
void PipelineHandler::releaseDevice([[maybe_unused]] Camera *camera)