## GstTask

GstTask — Abstraction of GStreamer streaming threads.

## Synopsis

    #include <gst/gst.h>

                        GstTask;
    void                (*GstTaskFunction)                  (void *data);
    enum                GstTaskState;
    #define             GST_TASK_BROADCAST                  (task)
    #define             GST_TASK_GET_COND                   (task)
    #define             GST_TASK_GET_LOCK                   (task)
    #define             GST_TASK_SIGNAL                     (task)
    #define             GST_TASK_STATE                      (task)
    #define             GST_TASK_WAIT                       (task)
    void                gst_task_cleanup_all                (void);
    GstTask*            gst_task_create                     (GstTaskFunction func,
                                                             gpointer data);
    GstTaskState        gst_task_get_state                  (GstTask *task);
    gboolean            gst_task_join                       (GstTask *task);
    gboolean            gst_task_pause                      (GstTask *task);
    void                gst_task_set_lock                   (GstTask *task,
                                                             GStaticRecMutex *mutex);
    gboolean            gst_task_start                      (GstTask *task);
    gboolean            gst_task_stop                       (GstTask *task);

## Object Hierarchy

      GObject
       +----GstObject
             +----GstTask

## 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 GStaticRecMutex 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.

A GstTask will repeadedly call the GstTaskFunction with the user data that was provided when creating the task with `gst_task_create()`. Before calling the function it will acquire the provided lock.

Stopping a task with `gst_task_stop()` will not immediatly 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 it the task is not running anymore.

Last reviewed on 2006-02-13 (0.10.4)

## Details

### GstTask

    typedef struct {
      GstTaskState     state;
      GCond 	  *cond;

      GStaticRecMutex *lock;

      GstTaskFunction  func;
      gpointer 	   data;

      gboolean	   running;
    } GstTask;

The GstTask object.

GstTaskState `state`; | the state of the task
GCond *`cond`; | used to pause/resume the task
GStaticRecMutex *`lock`; | The lock taken when iterating the taskfunction
GstTaskFunction `func`; | the function executed by this task
gpointer `data`; | data passed to the task function
gboolean `running`; | a flag indicating that the task is running.
gpointer `_gst_reserved`[GST_PADDING + 0]; |

### GstTaskFunction ()

    void                (*GstTaskFunction)                  (void *data);

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

`data` : | user data passed to the function

### enum GstTaskState

    typedef enum {
      GST_TASK_STARTED,
      GST_TASK_STOPPED,
      GST_TASK_PAUSED
    } GstTaskState;

The different states a task can be in

`GST_TASK_STARTED` | the task is started and running
`GST_TASK_STOPPED` | the task is stopped
`GST_TASK_PAUSED` | the task is paused

### GST_TASK_BROADCAST()

    #define GST_TASK_BROADCAST(task)	g_cond_breadcast(GST_TASK_GET_COND (task))

Send a broadcast signal to all waiting task conds

`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.

`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.

`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

`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.

`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

`task` : | Task to wait for

### 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 datastructures in testsuites.

MT safe.

### gst_task_create ()

    GstTask*            gst_task_create                     (GstTaskFunction func,
                                                             gpointer data);

Create a new Task that will repeadedly call the provided `func` with `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.

`func` : | The GstTaskFunction to use
`data` : | User data to pass to `func`
Returns : | A new GstTask. MT safe.

### gst_task_get_state ()

    GstTaskState        gst_task_get_state                  (GstTask *task);

Get the current state of the task.

`task` : | The GstTask to query
Returns : | The GstTaskState of the task 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.

`task` : | The GstTask to join
Returns : | TRUE if the task could be joined. MT safe.

### 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.

`task` : | The GstTask to pause
Returns : | TRUE if the task could be paused. MT safe.

### gst_task_set_lock ()

    void                gst_task_set_lock                   (GstTask *task,
                                                             GStaticRecMutex *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.

`task` : | The GstTask to use
`mutex` : | The GMutex to use

### 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 thsi function will return FALSE.

`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.

`task` : | The GstTask to stop
Returns : | TRUE if the task could be stopped. MT safe.

## See Also

GstElement, GstPad