Task

class Task(**properties: Any)

Superclasses: Object, InitiallyUnowned, Object

Task is used by Element and Pad to provide the data passing threads in a Pipeline.

A Pad will typically start a Task to push or pull data to/from the peer pads. Most source elements start a Task to push data. In some cases a demuxer element can start a Task to pull data from a peer element. This is typically done when the demuxer can perform random access on the upstream peer element for improved performance.

Although convenience functions exist on Pad to start/pause/stop tasks, it might sometimes be needed to create a Task manually if it is not related to a Pad.

Before the Task can be run, it needs a RecMutex that can be set with set_lock().

The task can be started, paused and stopped with start(), pause() and stop() respectively or with the set_state() function.

A Task will repeatedly call the TaskFunction with the user data that was provided when creating the task with new(). While calling the function it will acquire the provided lock. The provided lock is released when the task pauses or stops.

Stopping a task with stop() will not immediately make sure the task is not running anymore. Use join() to make sure the task is completely stopped and the thread is stopped.

After creating a Task, use unref() to free its resources. This can only be done when the task is not running anymore.

Task functions can send a Message to send out-of-band data to the application. The application can receive messages from the Bus in its mainloop.

For debugging purposes, the task will configure its object name as the thread name on Linux. Please note that the object name should be configured before the task is started; changing the object name after the task has been started, has no effect on the thread name.

Constructors

class Task

classmethod new(func: Callable[[Any], None], user_data: Any = None) → Task

Create a new Task that will repeatedly call the provided func with user_data as a parameter. Typically the task will run in a new thread.

The function cannot be changed after the task has been created. You must create a new Task to change the function.

This function will not yet create and start a thread. Use start() or pause() to create and start the GThread.

Before the task can be used, a RecMutex must be configured using the set_lock() function. This lock will always be acquired while func is called.

Parameters:

• func – The TaskFunction to use

• user_data – User data to pass to func

Methods

class Task

classmethod cleanup_all() → None

Wait for all tasks to be stopped. This is mainly used internally to ensure proper cleanup of internal data structures in test suites.

MT safe.

get_pool() → TaskPool

Get the TaskPool that this task will use for its streaming threads.

MT safe.

get_state() → TaskState

Get the current state of the task.

join() → bool

Joins task. After this call, it is safe to unref the task and clean up the lock set with set_lock().

The task will automatically be stopped with this call.

This function cannot be called from within a task function as this would cause a deadlock. The function will detect this and print a g_warning.

pause() → bool

Pauses task. This method can also be called on a task in the stopped state, in which case a thread will be started and will remain in the paused state. This function does not wait for the task to complete the paused state.

resume() → bool

Resume task in case it was paused. If the task was stopped, it will remain in that state and this function will return False.

Added in version 1.18.

set_enter_callback(enter_func: Callable[[Task, Thread, Any], None], user_data: Any = None) → None

Call enter_func when the task function of task is entered. user_data will be passed to enter_func and notify will be called when user_data is no longer referenced.

Parameters:

• enter_func – a TaskThreadFunc

• user_data – user data passed to enter_func

set_leave_callback(leave_func: Callable[[Task, Thread, Any], None], user_data: Any = None) → None

Call leave_func when the task function of task is left. user_data will be passed to leave_func and notify will be called when user_data is no longer referenced.

Parameters:

• leave_func – a TaskThreadFunc

• user_data – user data passed to leave_func

set_lock(mutex: RecMutex) → None

Set the mutex used by the task. The mutex will be acquired before calling the TaskFunction.

This function has to be called before calling pause() or start().

MT safe.

Parameters:

mutex – The RecMutex to use

set_pool(pool: TaskPool) → None

Set pool as the new GstTaskPool for task. Any new streaming threads that will be created by task will now use pool.

MT safe.

Parameters:

pool – a TaskPool

set_state(state: TaskState) → bool

Sets the state of task to state.

The task must have a lock associated with it using set_lock() when going to GST_TASK_STARTED or GST_TASK_PAUSED or this function will return False.

MT safe.

Parameters:

state – the new task state

start() → bool

Starts task. The task must have a lock associated with it using set_lock() or this function will return False.

stop() → bool

Stops task. This method merely schedules the task to stop and will not wait for the task to have completely stopped. Use join() to stop and wait for completion.

Fields

class Task

cond

Used to pause/resume the task

func

The function executed by this task

lock

The lock taken when iterating the task function

notify

GDestroyNotify for user_data

object

priv

running

A flag indicating that the task is running

state

The state of the task

thread

user_data

User_data passed to the task function