Re: C level mutices and condition variables

[Marius Vollmer <mvo@zagadka.ping.de>]

Neil Jerram <neil@ossau.uklinux.net> writes:

> - Why would you want "to have SCM data in a scm_t_mutex"? - isn't the
>   data that you are protecting access to normally a separate variable
>   (or set of variables) from the mutex itself?

I was thinking about data that is needed to implement the mutex
itself.  It would be nice to be able to use SCM values, I'd say, just
because a SCM string as the mutex name is nicer than a C string.

Concretely, I wanted to use SCM lists to implement the waiting queue
(to add fairness to POSIX mutices), mostly because SCM lists are
already there and why shouldn't I use them then?

> - What do you mean by not abstract enough?

You will declare scm_t_mutex variables and thus the size of the
scm_t_mutex structure can not change.  When we want to select mutex
implementations at run-time, that might be a (small) problem.  In any
case, I think it is better to hide mutices behind SCM values, just as
other data structures.

> - In "tell them to use the Scheme level mutices", who is "them", and

The people who use scm_t_mutex etc now.

>   would it be possible for them to use Scheme mutexes from C code, or
>   are you saying that people who need mutexes must code in Scheme?

They can code in C.  Instead of

   scm_t_mutex my_mutex;
   scm_mutex_init (&my_mutex);
   scm_mutex_lock (&my_mutex);

it would be

   SCM my_mutex = scm_make_mutex ();
   scm_lock_mutex (my_mutex);

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