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GStreamer 0.10 Core Reference Manual | ![]() |
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#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) 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);
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.
Last reviewed on 2006-02-13 (0.10.4)
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 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 |
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 |
typedef enum { GST_TASK_STARTED, GST_TASK_STOPPED, GST_TASK_PAUSED } GstTaskState;
The different states a task can be in
#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 |
#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 |
#define GST_TASK_GET_LOCK(task) (GST_TASK_CAST(task)->lock)
Get access to the task lock.
task : |
Task to get the lock of |
#define GST_TASK_SIGNAL(task) g_cond_signal(GST_TASK_GET_COND (task))
Signal the task cond
task : |
Task to signal |
#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 |
#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 |
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
|
Returns : | A new GstTask. MT safe. |
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 |
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
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 |
Since 0.10.24
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.
|
Since 0.10.24
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
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 |
user_data : |
user data passed to the callbacks |
notify : |
called when user_data is no longer referenced
|
Since 0.10.24
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. |
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
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.
|
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.
|
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.
|
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.
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