/*
doc: <routine name="rt_processor_subscribe_wait_condition" return_type="int" export="shared">
doc: <summary> Register for a notification when the memory region handled by processor 'self' may have changed.
doc: This is used to implement wait condition change signalling.
doc: The registration is only valid for a single notification and will be deleted by 'self' afterwards.
doc: Note: This feature is executed by the 'client' processor (i.e. thread), and can only be called when the
doc: supplier 'self' is synchronized with the client. </summary>
doc: <param name="self" type="struct rt_processor*"> The processor that will send the notification in the future. Must not be NULL. </param>
doc: <param name="client" type="struct rt_processor*"> The processor interested in wait condition changes. Must not be NULL. </param>
doc: <return> T_OK on success. T_NO_MORE_MEMORY in case of a memory allocation failure. </return>
doc: <thread_safety> Not safe. </thread_safety>
doc: <synchronization> Only call when 'self' is synchronized with 'client'. </synchronization>
doc: </routine>
*/
rt_shared int rt_processor_subscribe_wait_condition (struct rt_processor* self, struct rt_processor* client)
{
#ifdef EIF_ASSERTIONS
struct rt_private_queue* pq = NULL; /* For assertion checking. */
#endif
REQUIRE ("self_not_null", self);
REQUIRE ("client_not_null", client);
REQUIRE ("queue_available", T_OK == rt_queue_cache_retrieve (&client->cache, self, &pq));
REQUIRE ("synchronized", rt_private_queue_is_synchronized (pq));
return subscriber_list_t_extend (&self->wait_condition_subscribers, client);
}
/*
doc: <routine name="rt_request_group_wait" return_type="int" export="shared">
doc: <summary>
doc: Release all locks and wait for a change notification from any processor in the group.
doc: This feature is usually called after a wait condition fails.
doc: It can only be called when the request group is locked.
doc: Note: The wait() operation is blocking! </summary>
doc: <param name="self" type="struct rt_request_group*"> The request group struct. Must not be NULL. </param>
doc: <return> T_OK on success. T_NO_MORE_MEMORY if memory allocation fails, in which case the request group remains locked. </return>
doc: <thread_safety> Not safe. </thread_safety>
doc: <synchronization> None. </synchronization>
doc: <fixme> Instead of unlocking normally after the wait condition, we could have a special 'unlock-after-wait-condition-failure'.
doc: That way we can avoid sending unnecessary notifications after the evaluation of a wait condition. </fixme>
doc: </routine>
*/
rt_shared int rt_request_group_wait (struct rt_request_group* self)
{
size_t i, l_count = rt_request_group_count (self);
struct rt_processor* l_client = self->client;
int error = T_OK;
REQUIRE ("self_not_null", self);
REQUIRE ("sorted", self->is_sorted);
REQUIRE ("locked", self->is_locked);
/* Register the current client with the suppliers, such that we
* can later get a notification if a wait condition may have changed. */
for (i = 0; i < l_count; ++i) {
struct rt_private_queue* l_queue = rt_request_group_item (self, i);
/* We only register on queues which are currently synchronized.
* Those are the ones that have executed a query during the wait
* condition, and thus the only ones that matter.
* Moreover, because the suppliers are currently synchronized, we
* know that they cannot access their notification queue at the
* moment, so we can safely modify the list from this thread. */
if (rt_private_queue_is_synchronized (l_queue)) {
error = rt_private_queue_register_wait (l_queue, l_client);
/* We bail out if we can't register for a wait condition change. */
if (error != T_OK) {
return error;
}
}
}
/* Inform the GC that we're about to be blocked. */
EIF_ENTER_C;
/* Before we unlock the synchronized queues, we have to acquire the
* lock to our condition variable mutex. This has to happen before
* rt_request_group_unlock to avoid missed signals. */
RT_TRACE (eif_pthread_mutex_lock (l_client->wait_condition_mutex));
/* Release the locks on the suppliers. After this statement they can
* execute calls from other processors and signal back a wait condition
* change. If we wouldn't hold the lock acquired in the previous step,
* we might miss those signals and thus remain stuck in a wait condition
* forever. */
rt_request_group_unlock (self);
/* Now we perform the blocking wait on our condition.
* This also releases the mutex, such that our suppliers may send signals to it.
* Note: Usually these wait operations are performed inside a loop that checks whether
* the wait condition became true. Our loop is compiler-generated however,
* that's why we don't see it here. */
RT_TRACE (eif_pthread_cond_wait (l_client->wait_condition, l_client->wait_condition_mutex));
/* After the wakeup signal, we can release the mutex.
* We're not interested in any further signals, as we re-register anyway if the
* wait condition fails again. */
RT_TRACE (eif_pthread_mutex_unlock (l_client->wait_condition_mutex));
/* Synchronize with the GC again. */
EIF_EXIT_C;
RTGC;
/* Note: We do not clean up the registrations here, because it would involve
* unnecessary locking and a risk of deadlocks. Instead, the suppliers delete
* our registration during notification, and the GC will clean up any leftover registrations. */
ENSURE ("not_locked", !self->is_locked);
return error;
}
