@@ -116,19 +116,21 @@ available.
.. code:: cpp
- if (cm->cameras().empty()) {
+ auto cameras = cm->cameras();
+ if (cameras.empty()) {
std::cout << "No cameras were identified on the system."
<< std::endl;
cm->stop();
return EXIT_FAILURE;
}
- std::string cameraId = cm->cameras()[0]->id();
- camera = cm->get(cameraId);
+ std::string cameraId = cameras[0]->id();
+ auto camera = cm->get(cameraId);
/*
- * Note that is equivalent to:
- * camera = cm->cameras()[0];
+ * Note that `camera` may not compare equal to `cameras[0]`.
+ * In fact, it might simply be a `nullptr`, as the particular
+ * device might have disappeared (and reappeared) in the meantime.
*/
Once a camera has been selected an application needs to acquire an exclusive
@@ -39,9 +39,14 @@ CameraSession::CameraSession(CameraManager *cm,
{
char *endptr;
unsigned long index = strtoul(cameraId.c_str(), &endptr, 10);
- if (*endptr == '\0' && index > 0 && index <= cm->cameras().size())
- camera_ = cm->cameras()[index - 1];
- else
+
+ if (*endptr == '\0' && index > 0) {
+ auto cameras = cm->cameras();
+ if (index <= cameras.size())
+ camera_ = cameras[index - 1];
+ }
+
+ if (!camera_)
camera_ = cm->get(cameraId);
if (!camera_) {
@@ -385,13 +385,14 @@ gst_libcamera_src_open(GstLibcameraSrc *self)
return false;
}
} else {
- if (cm->cameras().empty()) {
+ auto cameras = cm->cameras();
+ if (cameras.empty()) {
GST_ELEMENT_ERROR(self, RESOURCE, NOT_FOUND,
("Could not find any supported camera on this system."),
("libcamera::CameraMananger::cameras() is empty"));
return false;
}
- cam = cm->cameras()[0];
+ cam = cameras[0];
}
GST_INFO_OBJECT(self, "Using camera '%s'", cam->id().c_str());
This is more efficient since only a single vector will be constructed, and furthermore, it prevents the TOCTOU issue that might arise when the list of cameras changes between the two queries. Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com> --- changes in v3 * drop std::move() from this change * extend note in documentation * limit scope of `cameras` in `CameraSession::CameraSession()` changes in v2 * fix code block in documentation * add comment noting that the camera may disappear --- Documentation/guides/application-developer.rst | 12 +++++++----- src/apps/cam/camera_session.cpp | 11 ++++++++--- src/gstreamer/gstlibcamerasrc.cpp | 5 +++-- 3 files changed, 18 insertions(+), 10 deletions(-) base-commit: fb74bb7df66b96dbe28702155cddfc96a1b30f78 -- 2.44.0