[Xenomai-core] [RFC] rt_task_join?

[Xenomai-core] [RFC] rt_task_join?

[Jan Kiszka]

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Hi all,

we ran into some issue where we have to wait on the termination of a
native real-time userspace thread during cleanup. This can be done in a
custom way of course, either via some polling on a flag or by blocking
on a standard posix semaphore that are signalled by the terminating
real-time thread. But maybe it is more useful to have a generic function
available with the native skin.

The problem is now that the pthreads underneath the real-time threads
are created with PTHREAD_CREATE_DETACHED. Changing this also changes the
semantic of other rt_task_xxx functions as posix then requires the
creator to call pthread_join (i.e. a new rt_task_join) in any case. A
better option might be to introduce a new mode bit T_JOINABLE to decide
if the related pthread should be created detached or not. Default would
remain PTHREAD_CREATE_DETACHED, if rt_task_join is to be used,
T_JOINABLE could be passed to rt_task_create.

What do you think, worth the effort?

Jan


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Re: [Xenomai-core] [RFC] rt_task_join?

[Jan Kiszka]

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Jan Kiszka wrote:
> Hi all,
> 
> we ran into some issue where we have to wait on the termination of a
> native real-time userspace thread during cleanup. This can be done in a
> custom way of course, either via some polling on a flag or by blocking
> on a standard posix semaphore that are signalled by the terminating
> real-time thread. But maybe it is more useful to have a generic function
> available with the native skin.
> 
> The problem is now that the pthreads underneath the real-time threads
> are created with PTHREAD_CREATE_DETACHED. Changing this also changes the
> semantic of other rt_task_xxx functions as posix then requires the
> creator to call pthread_join (i.e. a new rt_task_join) in any case. A
> better option might be to introduce a new mode bit T_JOINABLE to decide
> if the related pthread should be created detached or not. Default would
> remain PTHREAD_CREATE_DETACHED, if rt_task_join is to be used,
> T_JOINABLE could be passed to rt_task_create.
> 
> What do you think, worth the effort?
> 

Actually, the effort could be as simple as this (+ some docs) - as long
as I'm not overseeing some side effect right now.

Jan

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Index: include/native/task.h
===================================================================
--- include/native/task.h	(revision 245)
+++ include/native/task.h	(working copy)
@@ -35,18 +35,19 @@
 #define T_CPUMASK  0xff000000
 
 /* Status/mode flags. */
-#define T_BLOCKED XNPEND
-#define T_DELAYED XNDELAY
-#define T_READY   XNREADY
-#define T_DORMANT XNDORMANT
-#define T_STARTED XNSTARTED
-#define T_BOOST   XNBOOST
-#define T_LOCK    XNLOCK
-#define T_RRB     XNRRB
-#define T_NOSIG   XNASDI
-#define T_SHIELD  XNSHIELD
-#define T_WARNSW  XNTRAPSW
-#define T_PRIMARY XNTHREAD_SPARE0
+#define T_BLOCKED  XNPEND
+#define T_DELAYED  XNDELAY
+#define T_READY    XNREADY
+#define T_DORMANT  XNDORMANT
+#define T_STARTED  XNSTARTED
+#define T_BOOST    XNBOOST
+#define T_LOCK     XNLOCK
+#define T_RRB      XNRRB
+#define T_NOSIG    XNASDI
+#define T_SHIELD   XNSHIELD
+#define T_WARNSW   XNTRAPSW
+#define T_PRIMARY  XNTHREAD_SPARE0
+#define T_JOINABLE XNTHREAD_SPARE1
 
 /* Task hook types. */
 #define T_HOOK_START  XNHOOK_THREAD_START
@@ -268,6 +269,8 @@
 int rt_task_slice(RT_TASK *task,
 		  RTIME quantum);
 
+int rt_task_join(RT_TASK *task);
+
 #ifdef CONFIG_XENO_OPT_NATIVE_MPS
 
 ssize_t rt_task_send(RT_TASK *task,
Index: src/skins/native/task.c
===================================================================
--- src/skins/native/task.c	(revision 245)
+++ src/skins/native/task.c	(working copy)
@@ -127,7 +127,8 @@
 	stksize = PTHREAD_STACK_MIN;
 
     pthread_attr_setstacksize(&thattr,stksize);
-    pthread_attr_setdetachstate(&thattr,PTHREAD_CREATE_DETACHED);
+    if (!(mode & T_JOINABLE))
+	pthread_attr_setdetachstate(&thattr,PTHREAD_CREATE_DETACHED);
     pthread_attr_setschedpolicy(&thattr,SCHED_FIFO);
     param.sched_priority = sched_get_priority_max(SCHED_FIFO);
     pthread_attr_setschedparam(&thattr,&param);
@@ -331,6 +332,11 @@
 			     &quantum);
 }
 
+int rt_task_join (RT_TASK *task)
+{
+    return -pthread_join((pthread_t)task->opaque2, NULL);
+}
+
 #ifdef CONFIG_XENO_OPT_NATIVE_MPS
 
 ssize_t rt_task_send (RT_TASK *task,

Re: [Xenomai-core] [RFC] rt_task_join?

[Philippe Gerum]

Jan Kiszka wrote:
> Jan Kiszka wrote:
> 
>>Hi all,
>>
>>we ran into some issue where we have to wait on the termination of a
>>native real-time userspace thread during cleanup. This can be done in a
>>custom way of course, either via some polling on a flag or by blocking
>>on a standard posix semaphore that are signalled by the terminating
>>real-time thread. But maybe it is more useful to have a generic function
>>available with the native skin.
>>
>>The problem is now that the pthreads underneath the real-time threads
>>are created with PTHREAD_CREATE_DETACHED. Changing this also changes the
>>semantic of other rt_task_xxx functions as posix then requires the
>>creator to call pthread_join (i.e. a new rt_task_join) in any case. A
>>better option might be to introduce a new mode bit T_JOINABLE to decide
>>if the related pthread should be created detached or not. Default would
>>remain PTHREAD_CREATE_DETACHED, if rt_task_join is to be used,
>>T_JOINABLE could be passed to rt_task_create.
>>
>>What do you think, worth the effort?
>>
> 
> 
> Actually, the effort could be as simple as this (+ some docs) - as long
> as I'm not overseeing some side effect right now.
> 

Looks ok.

> 
> 
> ------------------------------------------------------------------------
> 
> Index: include/native/task.h
> ===================================================================
> --- include/native/task.h	(revision 245)
> +++ include/native/task.h	(working copy)
> @@ -35,18 +35,19 @@
>  #define T_CPUMASK  0xff000000
>  
>  /* Status/mode flags. */
> -#define T_BLOCKED XNPEND
> -#define T_DELAYED XNDELAY
> -#define T_READY   XNREADY
> -#define T_DORMANT XNDORMANT
> -#define T_STARTED XNSTARTED
> -#define T_BOOST   XNBOOST
> -#define T_LOCK    XNLOCK
> -#define T_RRB     XNRRB
> -#define T_NOSIG   XNASDI
> -#define T_SHIELD  XNSHIELD
> -#define T_WARNSW  XNTRAPSW
> -#define T_PRIMARY XNTHREAD_SPARE0
> +#define T_BLOCKED  XNPEND
> +#define T_DELAYED  XNDELAY
> +#define T_READY    XNREADY
> +#define T_DORMANT  XNDORMANT
> +#define T_STARTED  XNSTARTED
> +#define T_BOOST    XNBOOST
> +#define T_LOCK     XNLOCK
> +#define T_RRB      XNRRB
> +#define T_NOSIG    XNASDI
> +#define T_SHIELD   XNSHIELD
> +#define T_WARNSW   XNTRAPSW
> +#define T_PRIMARY  XNTHREAD_SPARE0
> +#define T_JOINABLE XNTHREAD_SPARE1
>  
>  /* Task hook types. */
>  #define T_HOOK_START  XNHOOK_THREAD_START
> @@ -268,6 +269,8 @@
>  int rt_task_slice(RT_TASK *task,
>  		  RTIME quantum);
>  
> +int rt_task_join(RT_TASK *task);
> +

Should move to the user-space section of the header file (i.e. !(KERNEL 
|| XENO_SIM))

>  #ifdef CONFIG_XENO_OPT_NATIVE_MPS
>  
>  ssize_t rt_task_send(RT_TASK *task,
> Index: src/skins/native/task.c
> ===================================================================
> --- src/skins/native/task.c	(revision 245)
> +++ src/skins/native/task.c	(working copy)
> @@ -127,7 +127,8 @@
>  	stksize = PTHREAD_STACK_MIN;
>  
>      pthread_attr_setstacksize(&thattr,stksize);
> -    pthread_attr_setdetachstate(&thattr,PTHREAD_CREATE_DETACHED);
> +    if (!(mode & T_JOINABLE))
> +	pthread_attr_setdetachstate(&thattr,PTHREAD_CREATE_DETACHED);
>      pthread_attr_setschedpolicy(&thattr,SCHED_FIFO);
>      param.sched_priority = sched_get_priority_max(SCHED_FIFO);
>      pthread_attr_setschedparam(&thattr,&param);
> @@ -331,6 +332,11 @@
>  			     &quantum);
>  }
>  
> +int rt_task_join (RT_TASK *task)
> +{
> +    return -pthread_join((pthread_t)task->opaque2, NULL);
> +}
> +
>  #ifdef CONFIG_XENO_OPT_NATIVE_MPS
>  
>  ssize_t rt_task_send (RT_TASK *task,
> 
> 
> ------------------------------------------------------------------------
> 
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> Xenomai-core@domain.hid
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-- 

Philippe.