Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> When exiting a process, rtdk buffers are not flushed. Fix that by
>>> introducing a destructor for the library which flushes the buffers.
>>>
>>> When forking, if the main thread has an rt_printf buffer, it is reused by
>>> the child, which is a good thing, however, it is not emptied, so could cause
>>> the same message to be printed twice. Fix that by emptying the main thread
>>> buffer upon fork.
>>>
>>> When spawning the rt_print thread, it uses a stack size of
>>> PTHREAD_STACK_MIN, which may be too small for printf to work reliably on
>>> some architectures, set the stack size to the
>>> empirically-known-to-be-working size of... 32Kb.
>>> ---
>>> src/rtdk/init.c | 5 +++++
>>> src/rtdk/internal.h | 1 +
>>> src/rtdk/rt_print.c | 21 ++++++++++++++++++++-
>>> 3 files changed, 26 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/src/rtdk/init.c b/src/rtdk/init.c
>>> index 2084c73..b864175 100644
>>> --- a/src/rtdk/init.c
>>> +++ b/src/rtdk/init.c
>>> @@ -22,3 +22,8 @@ static __attribute__ ((constructor)) void
>>> __init_rtdk(void)
>>> {
>>> __rt_print_init();
>>> }
>>> +
>>> +static __attribute__ ((destructor)) void __exit_rtdk(void)
>>> +{
>>> + __rt_print_exit();
>>> +}
>>> diff --git a/src/rtdk/internal.h b/src/rtdk/internal.h
>>> index bd15b2d..345d4fa 100644
>>> --- a/src/rtdk/internal.h
>>> +++ b/src/rtdk/internal.h
>>> @@ -23,6 +23,7 @@
>>> #include <sys/time.h>
>>>
>>> void __rt_print_init(void);
>>> +void __rt_print_exit(void);
>>>
>>> void __real_free(void *ptr);
>>> void *__real_malloc(size_t size);
>>> diff --git a/src/rtdk/rt_print.c b/src/rtdk/rt_print.c
>>> index c6b5c55..dae7d7b 100644
>>> --- a/src/rtdk/rt_print.c
>>> +++ b/src/rtdk/rt_print.c
>>> @@ -455,7 +455,7 @@ static void spawn_printer_thread(void)
>>> pthread_attr_t thattr;
>>>
>>> pthread_attr_init(&thattr);
>>> - pthread_attr_setstacksize(&thattr, PTHREAD_STACK_MIN);
>>> + pthread_attr_setstacksize(&thattr, 32768);
>> Mmh... maybe rather $something +PTHREAD_STACK_MIN?
>
> No, PTHREAD_STACK_MIN sucks, it is not appropriate, and have very
> varying values on different platforms. On some plaforms, with some
> versions of glibc, it is 4096, way too small, so that printf generates a
> segfault due to a stack overflow.
>
> However, due to the work done when solving the stack issue reported by
> Stefan, I hid the magic constants in a function called xeno_stacksize
> and xeno_stacksize(0) gives a reasonnable default value.
OK, then go for this service (is it already merged)?
>
>>> pthread_create(&printer_thread, &thattr, printer_loop, NULL);
>>> }
>>>
>>> @@ -464,6 +464,15 @@ static void forked_child_init(void)
>>> struct print_buffer *my_buffer = pthread_getspecific(buffer_key);
>>> struct print_buffer **pbuffer = &first_buffer;
>>>
>>> + if (my_buffer) {
>>> + /* Any content of my_buffer should be printed by our parent,
>>> + not us. */
>>> + memset(my_buffer->ring, 0, my_buffer->size);
>>> +
>>> + my_buffer->read_pos = 0;
>>> + my_buffer->write_pos = 0;
>>> + }
>>> +
>> Ack.
>>
>>> /* re-init to avoid finding it locked by some parent thread */
>>> pthread_mutex_init(&buffer_lock, NULL);
>>>
>>> @@ -518,3 +527,13 @@ void __rt_print_init(void)
>>> spawn_printer_thread();
>>> pthread_atfork(NULL, NULL, forked_child_init);
>>> }
>>> +
>>> +void __rt_print_exit(void)
>>> +{
>>> + if (buffers) {
>>> + /* Flush the buffers. Do not call print_buffers here
>>> + * since we do not know if our stack is big enough. */
>>> + nanosleep(&print_period, NULL);
>>> + nanosleep(&print_period, NULL);
>>> + }
>>> +}
>> IIRC, that's what cleanup_buffer is supposed to do, triggered by the
>> pthread key destruction. Can you explain why it failed in your scenario.
>
> pthread_key destruction is called when a thread is cancelled. My
> testcase was calling exit.
exit() does not trigger these cleanup hooks? Too bad.
> Besides, cleanup_buffer flushes the buffers
> from the context of the calling thread, which is a bad idea, due to the
> stack sizes situation.
If a thread requesting rt_printk services is not capable of performing
this work during it's cleanup, when there is no significant stack load,
I would say it's misconfigured /wrt stack size.
Jan
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