void
MR_lc_spawn_off_func(MR_LoopControl *lc, MR_Unsigned lcs_idx, MR_Code
*code_ptr)
{
MR_LoopControlSlot *lcs = &(lc->MR_lc_slots[lcs_idx]);
#if MR_DEBUG_LOOP_CONTROL
fprintf(stderr, "lc_spawn_off(%p, %d, %p) sp: %p\n",
lc, lcs_idx, code_ptr, MR_sp);
#endif
lcs->MR_lcs_context->MR_ctxt_resume = code_ptr;
lcs->MR_lcs_context->MR_ctxt_parent_sp = MR_sp;
MR_schedule_context(lcs->MR_lcs_context);
}
/*
** 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.
*/
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));
}
void
MR_lc_join(MR_LoopControl *lc, MR_Unsigned lcs_idx)
{
MR_LoopControlSlot *lcs;
MR_bool last_worker;
MR_Context *wakeup_context;
lcs = &(lc->MR_lc_slots[lcs_idx]);
#ifdef MR_DEBUG_LOOP_CONTROL
fprintf(stderr, "lc_join(%p, %d)\n", lc, lcs_idx);
#endif
lcs->MR_lcs_is_free = MR_TRUE;
lc->MR_lc_free_slot_hint = lcs_idx;
/* Ensure the slot is free before we perform the decrement. */
MR_CPU_SFENCE;
/*
** We have to determine if we're either the last of first workers to
** finish. To do this we cannot use atomic decrement since we need to do
** more than one comparison, Therefore we use a CAS.
*/
last_worker =
MR_atomic_dec_and_is_zero_int(&(lc->MR_lc_outstanding_workers));
/*
** If this is the last worker to finish, then take the lock before checking
** the master context field, otherwise we might race and end up never
** resuming the master.
*/
if (last_worker) {
MR_US_SPIN_LOCK(&(lc->MR_lc_master_context_lock));
/*
** Don't read the master field until after we have the lock
*/
MR_CPU_MFENCE;
}
/*
** If the master thread is suspended, wake it up, provided that either:
** - the loop has finished and this is the last worker to exit, or
** - the loop has not finished (so the master can create more work).
*/
if ((lc->MR_lc_master_context != NULL) &&
((lc->MR_lc_finished && last_worker) || (!lc->MR_lc_finished)))
{
/*
** Now take a lock and re-read the master context field.
*/
if (!last_worker) {
MR_US_SPIN_LOCK(&(lc->MR_lc_master_context_lock));
/*
** Don't read the master field until after we have the lock
*/
MR_CPU_MFENCE;
}
wakeup_context = lc->MR_lc_master_context;
lc->MR_lc_master_context = NULL;
MR_CPU_SFENCE; /* Make sure the field to nULL */
MR_US_UNLOCK(&(lc->MR_lc_master_context_lock));
if (wakeup_context != NULL) {
#ifdef MR_DEBUG_LOOP_CONTROL
fprintf(stderr, "Waking up master\n");
#endif
/*
** XXX: it is faster to switch to this context ourselves
** since we are going to unload our own context.
** Or we should switch to another worker context if there is one.
*/
MR_schedule_context(wakeup_context);
}
} else if (last_worker) {
MR_US_UNLOCK(&(lc->MR_lc_master_context_lock));
}
}