GstTask

GstTask — Abstraction of GStreamer streaming threads.

Synopsis

#include <gst/gst.h>

struct              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)
GstTask *           gst_task_create                     (GstTaskFunction func,
                                                         gpointer data);
void                gst_task_set_lock                   (GstTask *task,
                                                         GStaticRecMutex *mutex);
void                gst_task_set_priority               (GstTask *task,
                                                         GThreadPriority priority);
void                gst_task_set_pool                   (GstTask *task,
                                                         GstTaskPool *pool);
GstTaskPool *       gst_task_get_pool                   (GstTask *task);
                    GstTaskThreadCallbacks;
void                gst_task_set_thread_callbacks       (GstTask *task,
                                                         GstTaskThreadCallbacks *callbacks,
                                                         gpointer user_data,
                                                         GDestroyNotify notify);
GstTaskState        gst_task_get_state                  (GstTask *task);
gboolean            gst_task_set_state                  (GstTask *task,
                                                         GstTaskState state);
gboolean            gst_task_pause                      (GstTask *task);
gboolean            gst_task_start                      (GstTask *task);
gboolean            gst_task_stop                       (GstTask *task);
gboolean            gst_task_join                       (GstTask *task);
void                gst_task_cleanup_all                (void);

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 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_create(). 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 it 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 perposes, 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 2010-03-15 (0.10.29)

Details

struct GstTask

struct GstTask {
  GstTaskState     state;
  GCond           *cond;

  GStaticRecMutex *lock;

  GstTaskFunction  func;
  gpointer         data;

  gboolean         running;
};

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 task function

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

GstTaskFunction ()

void                (*GstTaskFunction)                  (void *data);

A function that will repeatedly 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_broadcast(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_create ()

GstTask *           gst_task_create                     (GstTaskFunction func,
                                                         gpointer data);

Create a new Task that will repeatedly 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.

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 GStaticRecMutex must be configured using the gst_task_set_lock() function. This lock will always be acquired while func is called.

func :

The GstTaskFunction to use

data :

User data to pass to func. [closure]

Returns :

A new GstTask. MT safe. [transfer full]

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_set_priority ()

void                gst_task_set_priority               (GstTask *task,
                                                         GThreadPriority priority);

Changes the priority of task to priority.

Note: try not to depend on task priorities.

MT safe.

task :

a GstTask

priority :

a new priority for task

Since 0.10.24


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.

task :

a GstTask

pool :

a GstTaskPool. [transfer none]

Since 0.10.24


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.

task :

a GstTask

Returns :

the GstTaskPool used by task. gst_object_unref() after usage. [transfer full]

Since 0.10.24


GstTaskThreadCallbacks

typedef struct {
  /* manage the lifetime of the thread */
  void      (*enter_thread)     (GstTask *task, GThread *thread, gpointer user_data);
  void      (*leave_thread)     (GstTask *task, GThread *thread, gpointer user_data);
} GstTaskThreadCallbacks;

Custom GstTask thread callback functions that can be installed.

enter_thread ()

a thread is entered, this callback is called when the new thread enters its function.

leave_thread ()

a thread is exiting, this is called when the thread is about to leave its function

Since 0.10.24


gst_task_set_thread_callbacks ()

void                gst_task_set_thread_callbacks       (GstTask *task,
                                                         GstTaskThreadCallbacks *callbacks,
                                                         gpointer user_data,
                                                         GDestroyNotify notify);

Set callbacks which will be executed when a new thread is needed, the thread function is entered and left and when the thread is joined.

By default a thread for task will be created from a default thread pool.

Objects can use custom GThreads or can perform additional configuration of the threads (such as changing the thread priority) by installing callbacks.

MT safe.

task :

The GstTask to use

callbacks :

a GstTaskThreadCallbacks pointer. [in]

user_data :

user data passed to the callbacks. [closure]

notify :

called when user_data is no longer referenced

Since 0.10.24


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_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.

task :

a GstTask

state :

the new task state

Returns :

TRUE if the state could be changed.

Since 0.10.24


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_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.

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.

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_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.

See Also

GstElement, GstPad