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application-development: threads: improve formatting

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Reynaldo H. Verdejo Pinochet 2017-09-06 21:23:06 -07:00
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markdown/application-development/advanced/threads.md
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@ -36,12 +36,12 @@ we can receive notifications of the tasks and pools.
## Configuring Threads in GStreamer ## Configuring Threads in GStreamer
A STREAM\_STATUS message is posted on the bus to inform you about the A `STREAM_STATUS` message is posted on the bus to inform you about the
status of the streaming threads. You will get the following information status of the streaming threads. You will get the following information
from the message: from the message:
- When a new thread is about to be created, you will be notified of - When a new thread is about to be created, you will be notified of
this with a GST\_STREAM\_STATUS\_TYPE\_CREATE type. It is then this with a `GST_STREAM_STATUS_TYPE_CREATE` type. It is then
possible to configure a `GstTaskPool` in the `GstTask`. The custom possible to configure a `GstTaskPool` in the `GstTask`. The custom
taskpool will provide custom threads for the task to implement the taskpool will provide custom threads for the task to implement the
streaming threads. streaming threads.
@ -64,10 +64,10 @@ We will now look at some examples in the next sections.
### Boost priority of a thread ### Boost priority of a thread
``` ```
.----------. .----------. .----------. .----------.
| faksesrc | | fakesink | | faksesrc | | fakesink |
| src->sink | | src->sink |
'----------' '----------' '----------' '----------'
``` ```
@ -77,24 +77,24 @@ starts the streaming thread for generating the fake data pushing them to
the peer fakesink. The flow for changing the priority would go like the peer fakesink. The flow for changing the priority would go like
this: this:
- When going from READY to PAUSED state, fakesrc will require a - When going from `READY` to `PAUSED` state, fakesrc will require a
streaming thread for pushing data into the fakesink. It will post a streaming thread for pushing data into the fakesink. It will post a
STREAM\_STATUS message indicating its requirement for a streaming `STREAM_STATUS` message indicating its requirement for a streaming
thread. thread.
- The application will react to the STREAM\_STATUS messages with a - The application will react to the `STREAM_STATUS` messages with a
sync bus handler. It will then configure a custom `GstTaskPool` on sync bus handler. It will then configure a custom `GstTaskPool` on
the `GstTask` inside the message. The custom taskpool is responsible the `GstTask` inside the message. The custom taskpool is responsible
for creating the threads. In this example we will make a thread with for creating the threads. In this example we will make a thread with
a higher priority. a higher priority.
- Alternatively, since the sync message is called in the thread - Alternatively, since the sync message is called in the thread
context, you can use thread ENTER/LEAVE notifications to change the context, you can use thread `ENTER`/`LEAVE` notifications to change the
priority or scheduling pollicy of the current thread. priority or scheduling pollicy of the current thread.
In a first step we need to implement a custom `GstTaskPool` that we can In a first step we need to implement a custom `GstTaskPool` that we can
configure on the task. Below is the implementation of a `GstTaskPool` configure on the task. Below is the implementation of a `GstTaskPool`
subclass that uses pthreads to create a SCHED\_RR real-time thread. Note subclass that uses pthreads to create a `SCHED_RR` real-time thread. Note
that creating real-time threads might require extra priveleges. that creating real-time threads might require extra priveleges.
``` c ``` c
@ -190,9 +190,6 @@ test_rt_pool_new (void)
return pool; return pool;
} }
``` ```
The important function to implement when writing an taskpool is the The important function to implement when writing an taskpool is the
@ -202,12 +199,10 @@ some threads around in a pool because creating and destroying threads is
not always the fastest operation. not always the fastest operation.
In a next step we need to actually configure the custom taskpool when In a next step we need to actually configure the custom taskpool when
the fakesrc needs it. For this we intercept the STREAM\_STATUS messages the fakesrc needs it. For this we intercept the `STREAM_STATUS` messages
with a sync handler. with a sync handler.
``` c ``` c
static GMainLoop* loop; static GMainLoop* loop;
static void static void
@ -320,9 +315,6 @@ main (int argc, char *argv[])
return 0; return 0;
} }
``` ```
Note that this program likely needs root permissions in order to create Note that this program likely needs root permissions in order to create
@ -330,7 +322,7 @@ real-time threads. When the thread can't be created, the state change
function will fail, which we catch in the application above. function will fail, which we catch in the application above.
When there are multiple threads in the pipeline, you will receive When there are multiple threads in the pipeline, you will receive
multiple STREAM\_STATUS messages. You should use the owner of the multiple `STREAM_STATUS` messages. You should use the owner of the
message, which is likely the pad or the element that starts the thread, message, which is likely the pad or the element that starts the thread,
to figure out what the function of this thread is in the context of the to figure out what the function of this thread is in the context of the
application. application.