Self-contained POSIX synchronization objects for RTEMS 4.12?

[Joel Sherrill]

On Tue, Sep 19, 2017 at 8:16 AM, Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> Hello,
>
> we have to make some trade-offs in the implementation with respect to the
> error checking. The operations get a pointer to the synchronization object,
> e.g.
>
> int sem_post(sem_t *sem);
>
> int pthread_mutex_lock(pthread_mutex_t *mutex);
>
> Do we want to check for NULL pointers?
>

Is newlib consistently using the non-NULL declaration on the argument?

Newlib/Cygwin folks have been pretty insistent that they do not want to
check for NULL on the shared methods.

Personally I hate to delete NULL argument pointer checks. Would a
long-term compromise be to move them to argument checking macros
that are enabled with --enable-rtems-debug?


>
> Do we want to check for other obviously invalid pointer values, e.g.
> SEM_FAILED?
>

IMO Yes


> Do we want to check if the object has been initialized?


Yes. We want to have predictable behavior.


>


> glibc uses no checks at all.
>

Performance over correctness? That doesn't seem like a good trade.


>
> FreeBSD checks that the object has been initialized. For this purpose it
> embeds a magic value field in the object structure. The drawback is that if
> we also do this, the objects are not zero-initialized and thus cannot
> reside in the BSS section.
>

This is an impossible trade. Some systems have big Flash and small RAM.
Others are the opposite.

I would rather follow the FreeBSD model and know the object is initialized.


>
> Destruction of synchronization objects in use is undefined behaviour
> according to POSIX. Do we want to flush waiting threads during destruction?
> This is a complex operation.
>

We have over 20 years of defined behavior in this case. I think
we flush and return the same error we always did. Otherwise,
we get a deadlock.


>
> What you think?
>
>
> --
> Sebastian Huber, embedded brains GmbH
>
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>
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