Re: [Minios-devel] [UNIKRAFT PATCH 5/8] lib/uksched: Revisit thread exiting logic

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Costin,

On 9/18/18 5:27 PM, Costin Lupu wrote:
> We use a list for terminated threads on all schedulers because it
> keeps references to those threads until wait will be called for
> them.
Just to make sure: your point is that since every scheduler will have to 
keep track of terminated threads, we might as well put it into the main 
uk_sched information instead of the private one, right?
> Signed-off-by: Costin Lupu <costin.lupu@xxxxxxxxx>
> ---
>   lib/uksched/include/uk/sched.h  |  1 +
>   lib/uksched/include/uk/thread.h |  4 ++++
>   lib/uksched/sched.c             |  7 ++++---
>   lib/ukschedcoop/schedcoop.c     | 11 +++--------
>   4 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/lib/uksched/include/uk/sched.h b/lib/uksched/include/uk/sched.h
> index 443dbf3..c3e2866 100644
> --- a/lib/uksched/include/uk/sched.h
> +++ b/lib/uksched/include/uk/sched.h
> @@ -87,6 +87,7 @@ struct uk_sched {
>   
>   	/* internal */
>         struct uk_thread idle;
> +       struct uk_thread_list exited_threads;
>         struct ukplat_ctx_callbacks plat_ctx_cbs;
>         struct uk_alloc *allocator;
>         struct uk_sched *next;
> diff --git a/lib/uksched/include/uk/thread.h b/lib/uksched/include/uk/thread.h
> index d28c458..7a1b630 100644
> --- a/lib/uksched/include/uk/thread.h
> +++ b/lib/uksched/include/uk/thread.h
> @@ -87,11 +87,15 @@ struct uk_thread *uk_thread_current(void)
>   }
>   
>   #define RUNNABLE_FLAG   0x00000001
> +#define EXITED_FLAG     0x00000002
>   
>   #define is_runnable(_thread)    ((_thread)->flags &   RUNNABLE_FLAG)
>   #define set_runnable(_thread)   ((_thread)->flags |=  RUNNABLE_FLAG)
>   #define clear_runnable(_thread) ((_thread)->flags &= ~RUNNABLE_FLAG)
>   
> +#define is_exited(_thread)      ((_thread)->flags &   EXITED_FLAG)
> +#define set_exited(_thread)     ((_thread)->flags |=  EXITED_FLAG)
> +
>   int uk_thread_init(struct uk_thread *thread,
>                 struct ukplat_ctx_callbacks *cbs, struct uk_alloc *allocator,
>                 const char *name, void *stack,
> diff --git a/lib/uksched/sched.c b/lib/uksched/sched.c
> index 968723c..c5b7c9f 100644
> --- a/lib/uksched/sched.c
> +++ b/lib/uksched/sched.c
> @@ -122,6 +122,7 @@ struct uk_sched *uk_sched_create(struct uk_alloc *a, size_t 
> prv_size)
>         }
>   
>   	sched->allocator = a;
> +       UK_TAILQ_INIT(&sched->exited_threads);
>         sched->prv = (void *) sched + sizeof(struct uk_sched);
>   
>   	return sched;
> @@ -217,6 +218,9 @@ void uk_sched_thread_destroy(struct uk_sched *sched, struct 
> uk_thread *thread)
>   {
>         UK_ASSERT(sched != NULL);
>         UK_ASSERT(thread != NULL);
> +       UK_ASSERT(is_exited(thread));
I don't like that this patch introduces an assertion on is_exited, but 
never calls set_exited. This means that at this revision, any call to 
uk_sched_thread_destroy will immediately crash with an assertion error. 
That might be really nasty if we ever end up tracking a bug during 
bisecting and end up with this revision.
Instead, I suggest you introduce this UK_ASSERT when you introduce more 
of the scheduling logic in the next patch ("Add support for waiting 
threads"), because in general, it makes a lot of sense as an assertion.
> +
> +       UK_TAILQ_REMOVE(&sched->exited_threads, thread, thread_list);
>   
>   	uk_free(sched->allocator, thread->sched_info);
>         uk_thread_fini(thread, sched->allocator);
> @@ -238,9 +242,6 @@ void uk_sched_thread_exit(void)
>         struct uk_thread *thread;
>   
>   	thread = uk_thread_current();
> -
> -       uk_printd(DLVL_INFO, "Thread \"%s\" exited.\n", thread->name);
> -
>         UK_ASSERT(thread->sched);
>         uk_sched_thread_remove(thread->sched, thread);
>         UK_CRASH("Error stopping thread.");
> diff --git a/lib/ukschedcoop/schedcoop.c b/lib/ukschedcoop/schedcoop.c
> index f616330..a2bf2ad 100644
> --- a/lib/ukschedcoop/schedcoop.c
> +++ b/lib/ukschedcoop/schedcoop.c
> @@ -37,7 +37,6 @@
>   
>   struct schedcoop_private {
>         struct uk_thread_list thread_list;
> -       struct uk_thread_list exited_threads;
>         int threads_started;
>   };
>   
> @@ -124,12 +123,9 @@ static void schedcoop_schedule(struct uk_sched *s)
>         if (prev != next)
>                 uk_sched_thread_switch(s, prev, next);
>   
> -	UK_TAILQ_FOREACH_SAFE(thread, &prv->exited_threads, thread_list, tmp) {
> -               if (thread != prev) {
> -                       UK_TAILQ_REMOVE(&prv->exited_threads,
> -                                       thread, thread_list);
> +       UK_TAILQ_FOREACH_SAFE(thread, &s->exited_threads, thread_list, tmp) {
> +               if (thread != prev)
>                         uk_thread_destroy(thread);
> -               }
>         }
>   }
>   
> @@ -166,7 +162,7 @@ static void schedcoop_thread_remove(struct uk_sched *s, struct uk_thread *t)
>         clear_runnable(t);
>   
>   	/* Put onto exited list */
> -       UK_TAILQ_INSERT_HEAD(&prv->exited_threads, t, thread_list);
> +       UK_TAILQ_INSERT_HEAD(&s->exited_threads, t, thread_list);
>   
>   	ukplat_lcpu_restore_irqf(flags);
>   
> @@ -211,7 +207,6 @@ struct uk_sched *uk_schedcoop_init(struct uk_alloc *a)
>         ukplat_ctx_callbacks_init(&sched->plat_ctx_cbs, ukplat_ctx_sw);
>   
>   	prv = sched->prv;
> -       UK_TAILQ_INIT(&prv->exited_threads);
>         UK_TAILQ_INIT(&prv->thread_list);
>         prv->threads_started = 0;
>   
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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