GstTask: GStreamer 1.0 Core Reference Manual

## GstTask GstTask — Abstraction of GStreamer streaming threads. |

## Functions

void | (*GstTaskFunction) ()
#define | GST_TASK_BROADCAST()
#define | GST_TASK_GET_COND()
#define | GST_TASK_GET_LOCK()
#define | GST_TASK_SIGNAL()
#define | GST_TASK_STATE()
#define | GST_TASK_WAIT()
GstTask * | gst_task_new ()
void | gst_task_set_lock ()
void | gst_task_set_pool ()
GstTaskPool * | gst_task_get_pool ()
void | (*GstTaskThreadFunc) ()
void | gst_task_set_enter_callback ()
void | gst_task_set_leave_callback ()
GstTaskState | gst_task_get_state ()
gboolean | gst_task_set_state ()
gboolean | gst_task_pause ()
gboolean | gst_task_start ()
gboolean | gst_task_stop ()
gboolean | gst_task_join ()
void | gst_task_cleanup_all ()

## 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.

## 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