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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef MEDIA_GPU_V4L2_V4L2_DEVICE_POLLER_H_
#define MEDIA_GPU_V4L2_V4L2_DEVICE_POLLER_H_
#include <atomic>
#include "base/callback_forward.h"
#include "base/sequence_checker.h"
#include "base/synchronization/waitable_event.h"
#include "base/task/sequenced_task_runner.h"
#include "base/threading/thread.h"
namespace media {
class V4L2Device;
// Allows a client to poll() on a given V4L2Device and be signaled when
// a buffer is ready to be dequeued or a V4L2 event has been received. Polling
// is done on a dedicated thread, and notifications are delivered in the form of
// a callback to the listener's sequence.
//
// All the methods of this class (with the exception of the constructor) must be
// called from the same sequence.
//
// Note that the service callback may also be called when no particular event
// occurred due to the way poll() works. It is the responsibility of the caller
// to call SchedulePoll() again if there may still be pending events.
class V4L2DevicePoller {
public:
// Callback to be called when buffer ready/V4L2 event has potentially been
// polled. |event| is set if a V4L2 event has been detected.
using EventCallback = base::RepeatingCallback<void(bool event)>;
// Create a poller for |device|, using a thread named |thread_name|.
// Notification won't start until |StartPolling()| is called.
V4L2DevicePoller(V4L2Device* const device, const std::string& thread_name);
~V4L2DevicePoller();
// Starts polling. |event_callback| will be posted on the caller's sequence
// every time an event occurs. The client is then responsible for consuming
// all pending events in that callback. If new events may still happen after
// the callback has run, the client must call |SchedulePoll()| again in order
// to be notified for them.
//
// If an error occurs during polling, |error_callback| will be posted on the
// caller's sequence.
bool StartPolling(EventCallback event_callback,
base::RepeatingClosure error_callback);
// Stop polling and stop the thread. The poller won't post any new event to
// the caller's sequence after this method has returned.
bool StopPolling();
// Returns true if currently polling, false otherwise.
bool IsPolling() const;
// Attempts polling the V4L2 device. This method should be called whenever
// doing something that may trigger an event of interest (buffer dequeue or
// V4L2 event), for instance queueing a buffer. In the absence of a pending
// event, poll() will return immediately and the service callback will be
// posted to the caller's sequence. The client is then responsible for calling
// this method again when it is interested in receiving events.
void SchedulePoll();
private:
// Perform a poll() on |device_| and post either |service_task_| or
// |error_callback_| on the client's sequence when poll() returns.
void DevicePollTask();
// V4L2 device we are polling.
V4L2Device* const device_;
// Thread on which polling is done.
base::Thread poll_thread_;
// Callback to post to the client's sequence when an event occurs.
EventCallback event_callback_;
// Closure to post to the client's sequence when an error occurs.
base::RepeatingClosure error_callback_;
// Client sequence's task runner, where closures are posted.
scoped_refptr<base::SequencedTaskRunner> client_task_runner_;
// Since poll() returns immediately if no buffers have been queued, we cannot
// rely on it to pause the polling thread until an event occurs. Instead,
// the polling thread will wait on this WaitableEvent (signaled by
// |SchedulePoll| before calling poll(), so we only call it when we are
// actually waiting for an event.
base::WaitableEvent trigger_poll_;
// Set to true when we wish to stop polling, instructing the poller thread
// to break its loop.
std::atomic_bool stop_polling_;
SEQUENCE_CHECKER(client_sequence_checker_);
};
} // namespace media
#endif // MEDIA_GPU_V4L2_V4L2_DEVICE_POLLER_H_