[m-rev.] for review: support STM in low level grades

[Ben Mellor]

> > +#if !defined(MR_HIGHLEVEL_CODE)
> > +/*
> > +** In the low level C grades, the "condition variable" created when an STM
> > +** transaction blocks is actually a pointer to the transaction log.
> > "Signalling" +** it consists of going through the STM variables listed in
> > the log and removing +** the waiters attached to them for the context
> > listed in the log. After this, +** the context can be safely rescheduled.
> > +*/
> 
> Are these over-long lines?

I thought no, as they were 80 characters, but I see the coding standard
specifies 79. I've fixed them.
 
> > +void
> > +MR_STM_condvar_signal(MR_STM_ConditionVar *cvar)
> > +{
> > +    /*
> > +    ** Calling MR_STM_unwait here should be safe, as this signalling is
> > called
> > +    ** in response to a commit, while the committing thread holds the
> > global
> > +    ** STM lock. Note that a MR_STM_ConditionVar IS a MR_STM_TransLog if
> > +    ** MR_HIGHLEVEL_CODE is not defined, which is why cvar is passed twice.
> > +    */
> > +    MR_STM_unwait(cvar, cvar);
> > +
> > +#if defined(MR_STM_DEBUG)
> > +        fprintf(stderr, "STM RESCHEDULING: log <0x%.8lx>\n",
> > (MR_Word)cvar); +#endif
> >  
> > +    MR_schedule_context(MR_STM_context_from_condvar(cvar));
> >  }
> > +
> > +#endif
> 
> Please add a warning to the prototype for MR_STM_condvar_signal to inform
> anyone calling this function that they must first have the global STM lock as
> mentioned in your comment.

/*
** NOTE: The global STM lock (MR_STM_lock) must be held when calling this
** function, as it manipulates the STM variable waiter lists.
*/

> > +    extern void MR_STM_condvar_signal(MR_STM_ConditionVar *cvar);
> > +
> > +    #define MR_STM_context_from_condvar(x)      (x->MR_STM_tl_thread)
> >  
> >  #endif /* !MR_HIGHLEVEL_CODE */
> 
> Why is MR_STM_condvar_signal defined as 'extern'?

Absent-mindedness. I've removed the extern.

Cheers
-- Ben
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