libcamera: libcamera::Fence Class Reference

libcamera v0.0.5 Supporting cameras in Linux since 2019

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Public Member Functions | List of all members
libcamera::Fence Class Reference

Synchronization primitive to manage resources. More...

## Public Member Functions
| Fence (UniqueFD fd)
| Create a Fence.
bool | isValid () const
| Check if a Fence is valid.
const UniqueFD & | fd () const
| Retrieve a constant reference to the file descriptor.
UniqueFD | release ()
| Release the ownership of the file descriptor.

## Detailed Description

Synchronization primitive to manage resources.

The Fence class models a synchronization primitive that can be used by applications to explicitly synchronize resource usage, and can be shared by multiple processes.

Fences are most commonly used in association with frame buffers. A FrameBuffer can be associated with a Fence so that the library can wait for the Fence to be signalled before allowing the camera device to actually access the memory area described by the FrameBuffer.

See also
  Request::addBuffer()

By using a fence, applications can then synchronize between frame buffer consumers and producers, as for example a display device and a camera, to guarantee that a new data transfers only happen once the existing frames have been displayed.

A Fence can be realized by different event notification primitives, the most common of which is represented by waiting for read events to happen on a kernel sync file. This is currently the only mechanism supported by libcamera, but others can be implemented by extending or subclassing this class and implementing opportune handling in the core library.

## Constructor & Destructor Documentation

## ◆ Fence()

libcamera::Fence::Fence | ( | UniqueFD | fd | ) |

Create a Fence.

Parameters

  [in] | fd | The fence file descriptor

The file descriptor ownership is moved to the Fence.

## Member Function Documentation

## ◆ fd()

libcamera::Fence::fd | ( |  | ) | const
| inline

Retrieve a constant reference to the file descriptor.

Returns
  A const reference to the fence file descriptor

## ◆ isValid()

libcamera::Fence::isValid | ( |  | ) | const
| inline

Check if a Fence is valid.

A Fence is valid if the file descriptor it wraps is valid.

Returns
  True if the Fence is valid, false otherwise

## ◆ release()

libcamera::Fence::release | ( |  | ) |
| inline

Release the ownership of the file descriptor.

Release the ownership of the wrapped file descriptor by returning it to the caller.

Returns
  The wrapper UniqueFD

The documentation for this class was generated from the following files:

- include/libcamera/fence.h
- src/libcamera/fence.cpp