GstTask

GstTask — Abstraction of GStreamer streaming threads.

Functions

Types and Values

struct GstTask
enum GstTaskState

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstTask

Includes

#include <gst/gst.h>

Description

GstTask is used by GstElement and GstPad to provide the data passing threads in a GstPipeline.

A GstPad will typically start a GstTask to push or pull data to/from the peer pads. Most source elements start a GstTask to push data. In some cases a demuxer element can start a GstTask 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 GstPad to start/pause/stop tasks, it might sometimes be needed to create a GstTask manually if it is not related to a GstPad.

Before the GstTask can be run, it needs a GRecMutex that can be set with gst_task_set_lock().

The task can be started, paused and stopped with gst_task_start(), gst_task_pause() and gst_task_stop() respectively or with the gst_task_set_state() function.

A GstTask will repeatedly call the GstTaskFunction with the user data that was provided when creating the task with gst_task_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 gst_task_stop() will not immediately make sure the task is not running anymore. Use gst_task_join() to make sure the task is completely stopped and the thread is stopped.

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

Task functions can send a GstMessage to send out-of-band data to the application. The application can receive messages from the GstBus 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.

Last reviewed on 2012-03-29 (0.11.3)

Functions

GstTaskFunction ()

void
(*GstTaskFunction) (gpointer user_data);

A function that will repeatedly be called in the thread created by a GstTask.

Parameters

user_data

user data passed to the function

 

GST_TASK_BROADCAST()

#define GST_TASK_BROADCAST(task)        g_cond_broadcast(GST_TASK_GET_COND (task))

Send a broadcast signal to all waiting task conds

Parameters

task

Task to broadcast

 

GST_TASK_GET_COND()

#define GST_TASK_GET_COND(task)         (&GST_TASK_CAST(task)->cond)

Get access to the cond of the task.

Parameters

task

Task to get the cond of

 

GST_TASK_GET_LOCK()

#define GST_TASK_GET_LOCK(task)         (GST_TASK_CAST(task)->lock)

Get access to the task lock.

Parameters

task

Task to get the lock of

 

GST_TASK_SIGNAL()

#define GST_TASK_SIGNAL(task)           g_cond_signal(GST_TASK_GET_COND (task))

Signal the task cond

Parameters

task

Task to signal

 

GST_TASK_STATE()

#define GST_TASK_STATE(task)            (GST_TASK_CAST(task)->state)

Get access to the state of the task.

Parameters

task

Task to get the state of

 

GST_TASK_WAIT()

#define GST_TASK_WAIT(task)             g_cond_wait(GST_TASK_GET_COND (task), GST_OBJECT_GET_LOCK (task))

Wait for the task cond to be signalled

Parameters

task

Task to wait for

 

gst_task_new ()

GstTask *
gst_task_new (GstTaskFunction func,
              gpointer user_data,
              GDestroyNotify notify);

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 GstTask to change the function.

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

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

Parameters

func

The GstTaskFunction to use

 

user_data

User data to pass to func

 

notify

the function to call when user_data is no longer needed.

 

Returns

A new GstTask.

MT safe.

[transfer full]


gst_task_set_lock ()

void
gst_task_set_lock (GstTask *task,
                   GRecMutex *mutex);

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

This function has to be called before calling gst_task_pause() or gst_task_start().

MT safe.

Parameters

task

The GstTask to use

 

mutex

The GRecMutex to use

 

gst_task_set_pool ()

void
gst_task_set_pool (GstTask *task,
                   GstTaskPool *pool);

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

task

a GstTask

 

pool

a GstTaskPool.

[transfer none]

gst_task_get_pool ()

GstTaskPool *
gst_task_get_pool (GstTask *task);

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

MT safe.

Parameters

task

a GstTask

 

Returns

the GstTaskPool used by task . gst_object_unref() after usage.

[transfer full]


GstTaskThreadFunc ()

void
(*GstTaskThreadFunc) (GstTask *task,
                      GThread *thread,
                      gpointer user_data);

Custom GstTask thread callback functions that can be installed.

Parameters

task

The GstTask

 

thread

The GThread

 

user_data

user data

 

gst_task_set_enter_callback ()

void
gst_task_set_enter_callback (GstTask *task,
                             GstTaskThreadFunc enter_func,
                             gpointer user_data,
                             GDestroyNotify notify);

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

task

The GstTask to use

 

enter_func

a GstTaskThreadFunc.

[in]

user_data

user data passed to enter_func

 

notify

called when user_data is no longer referenced

 

gst_task_set_leave_callback ()

void
gst_task_set_leave_callback (GstTask *task,
                             GstTaskThreadFunc leave_func,
                             gpointer user_data,
                             GDestroyNotify notify);

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

task

The GstTask to use

 

leave_func

a GstTaskThreadFunc.

[in]

user_data

user data passed to leave_func

 

notify

called when user_data is no longer referenced

 

gst_task_get_state ()

GstTaskState
gst_task_get_state (GstTask *task);

Get the current state of the task.

Parameters

task

The GstTask to query

 

Returns

The GstTaskState of the task

MT safe.


gst_task_set_state ()

gboolean
gst_task_set_state (GstTask *task,
                    GstTaskState state);

Sets the state of task to state .

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

MT safe.

Parameters

task

a GstTask

 

state

the new task state

 

Returns

TRUE if the state could be changed.


gst_task_pause ()

gboolean
gst_task_pause (GstTask *task);

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.

Parameters

task

The GstTask to pause

 

Returns

TRUE if the task could be paused.

MT safe.


gst_task_start ()

gboolean
gst_task_start (GstTask *task);

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

Parameters

task

The GstTask to start

 

Returns

TRUE if the task could be started.

MT safe.


gst_task_stop ()

gboolean
gst_task_stop (GstTask *task);

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

Parameters

task

The GstTask to stop

 

Returns

TRUE if the task could be stopped.

MT safe.


gst_task_join ()

gboolean
gst_task_join (GstTask *task);

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

Parameters

task

The GstTask to join

 

Returns

TRUE if the task could be joined.

MT safe.


gst_task_cleanup_all ()

void
gst_task_cleanup_all (void);

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.

Types and Values

struct GstTask

struct GstTask {
  GstTaskState     state;
  GCond            cond;

  GRecMutex       *lock;

  GstTaskFunction  func;
  gpointer         user_data;
  GDestroyNotify   notify;

  gboolean         running;
};

The GstTask object.

Members

GstTaskState state;

the state of the task

 

GCond cond;

used to pause/resume the task

 

GRecMutex *lock;

The lock taken when iterating the task function

 

GstTaskFunction func;

the function executed by this task

 

gpointer user_data;

user_data passed to the task function

 

GDestroyNotify notify;

GDestroyNotify for user_data

 

gboolean running;

a flag indicating that the task is running

 

enum GstTaskState

The different states a task can be in

Members

GST_TASK_STARTED

the task is started and running

 

GST_TASK_STOPPED

the task is stopped

 

GST_TASK_PAUSED

the task is paused

 

See Also

GstElement, GstPad