}
/**
- * Choose the next thread in the replay sequence.
+ * @brief Choose the next thread to execute.
*
- * If the replay sequence has reached the 'diverge' point, returns a thread
- * from the backtracking set. Otherwise, simply returns the next thread in the
- * sequence that is being replayed.
+ * This function chooses the next thread that should execute. It can force the
+ * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
+ * followed by a THREAD_START, or it can enforce execution replay/backtracking.
+ * The model-checker may have no preference regarding the next thread (i.e.,
+ * when exploring a new execution ordering), in which case this will return
+ * NULL.
+ * @param curr The current ModelAction. This action might guide the choice of
+ * next thread.
+ * @return The next thread to run. If the model-checker has no preference, NULL.
*/
-Thread * ModelChecker::get_next_replay_thread()
+Thread * ModelChecker::get_next_thread(ModelAction *curr)
{
thread_id_t tid;
+ /* Do not split atomic actions. */
+ if (curr->is_rmwr())
+ return thread_current();
+ /* The THREAD_CREATE action points to the created Thread */
+ else if (curr->get_type() == THREAD_CREATE)
+ return (Thread *)curr->get_location();
+
/* Have we completed exploring the preselected path? */
if (diverge == NULL)
return NULL;
{
ModelAction *prev;
Node *node;
- Thread *t = get_thread(act->get_tid());
+ Thread *t = get_thread(act);
prev = get_last_conflict(act);
if (prev == NULL)
return next;
}
+/**
+ * Processes a read or rmw model action.
+ * @param curr is the read model action to process.
+ * @param th is the thread
+ * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
+ * @return True if processing this read updates the mo_graph.
+ */
+
+bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
+ uint64_t value;
+ bool updated=false;
+ while(true) {
+ const ModelAction *reads_from = curr->get_node()->get_read_from();
+ if (reads_from != NULL) {
+ value = reads_from->get_value();
+ /* Assign reads_from, perform release/acquire synchronization */
+ curr->read_from(reads_from);
+ if (!second_part_of_rmw) {
+ check_recency(curr,false);
+ }
+
+ bool r_status=r_modification_order(curr,reads_from);
+
+ if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
+ mo_graph->rollbackChanges();
+ too_many_reads=false;
+ continue;
+ }
+
+ mo_graph->commitChanges();
+ updated |= r_status;
+ } else {
+ /* Read from future value */
+ value = curr->get_node()->get_future_value();
+ modelclock_t expiration = curr->get_node()->get_future_value_expiration();
+ curr->read_from(NULL);
+ Promise *valuepromise = new Promise(curr, value, expiration);
+ promises->push_back(valuepromise);
+ }
+ th->set_return_value(value);
+ return updated;
+ }
+}
+
/**
* This is the heart of the model checker routine. It performs model-checking
* actions corresponding to a given "current action." Among other processes, it
second_part_of_rmw = true;
delete curr;
curr = tmp;
+ compute_promises(curr);
} else {
ModelAction *tmp = node_stack->explore_action(curr);
if (tmp) {
}
}
- /* Assign 'creation' parent */
- if (curr->get_type() == THREAD_CREATE) {
+ /* Thread specific actions */
+ switch(curr->get_type()) {
+ case THREAD_CREATE: {
Thread *th = (Thread *)curr->get_location();
th->set_creation(curr);
- } else if (curr->get_type() == THREAD_JOIN) {
- Thread *wait, *join;
- wait = get_thread(curr->get_tid());
- join = (Thread *)curr->get_location();
- if (!join->is_complete())
- scheduler->wait(wait, join);
- } else if (curr->get_type() == THREAD_FINISH) {
- Thread *th = get_thread(curr->get_tid());
+ break;
+ }
+ case THREAD_JOIN: {
+ Thread *waiting, *blocking;
+ waiting = get_thread(curr);
+ blocking = (Thread *)curr->get_location();
+ if (!blocking->is_complete()) {
+ blocking->push_wait_list(curr);
+ scheduler->sleep(waiting);
+ }
+ break;
+ }
+ case THREAD_FINISH: {
+ Thread *th = get_thread(curr);
while (!th->wait_list_empty()) {
- Thread *wake = th->pop_wait_list();
+ ModelAction *act = th->pop_wait_list();
+ Thread *wake = get_thread(act);
scheduler->wake(wake);
}
th->complete();
+ break;
}
-
- /* Deal with new thread */
- if (curr->get_type() == THREAD_START)
+ case THREAD_START: {
check_promises(NULL, curr->get_cv());
+ break;
+ }
+ default:
+ break;
+ }
+
+ Thread *th = get_thread(curr);
- /* Assign reads_from values */
- Thread *th = get_thread(curr->get_tid());
- uint64_t value = VALUE_NONE;
bool updated = false;
if (curr->is_read()) {
- while(true) {
- const ModelAction *reads_from = curr->get_node()->get_read_from();
- if (reads_from != NULL) {
- value = reads_from->get_value();
- /* Assign reads_from, perform release/acquire synchronization */
- curr->read_from(reads_from);
- if (!second_part_of_rmw)
- check_recency(curr,false);
-
- bool r_status=r_modification_order(curr,reads_from);
+ updated=process_read(curr, th, second_part_of_rmw);
+ }
- if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
- mo_graph->rollbackChanges();
- too_many_reads=false;
- continue;
- }
+ if (curr->is_write()) {
+ bool updated_mod_order=w_modification_order(curr);
+ bool updated_promises=resolve_promises(curr);
+ updated=updated_mod_order|updated_promises;
- mo_graph->commitChanges();
- updated |= r_status;
- } else {
- /* Read from future value */
- value = curr->get_node()->get_future_value();
- curr->read_from(NULL);
- Promise *valuepromise = new Promise(curr, value);
- promises->push_back(valuepromise);
- }
- break;
- }
- } else if (curr->is_write()) {
- if (w_modification_order(curr))
- updated = true;
- if (resolve_promises(curr))
- updated = true;
mo_graph->commitChanges();
+ th->set_return_value(VALUE_NONE);
}
if (updated)
resolve_release_sequences(curr->get_location());
- th->set_return_value(value);
-
/* Add action to list. */
if (!second_part_of_rmw)
add_action_to_lists(curr);
Node *currnode = curr->get_node();
Node *parnode = currnode->get_parent();
- if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
- !currnode->future_value_empty() || !currnode->promise_empty())
- if (!priv->next_backtrack || *curr > *priv->next_backtrack)
- priv->next_backtrack = curr;
+ if ((!parnode->backtrack_empty() ||
+ !currnode->read_from_empty() ||
+ !currnode->future_value_empty() ||
+ !currnode->promise_empty())
+ && (!priv->next_backtrack ||
+ *curr > *priv->next_backtrack)) {
+ priv->next_backtrack = curr;
+ }
set_backtracking(curr);
- /* Do not split atomic actions. */
- if (curr->is_rmwr())
- return thread_current();
- /* The THREAD_CREATE action points to the created Thread */
- else if (curr->get_type() == THREAD_CREATE)
- return (Thread *)curr->get_location();
- else
- return get_next_replay_thread();
+ return get_next_thread(curr);
+}
+
+bool ModelChecker::promises_expired() {
+ for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
+ Promise *promise = (*promises)[promise_index];
+ if (promise->get_expiration()<priv->used_sequence_numbers) {
+ return true;
+ }
+ }
+ return false;
}
/** @returns whether the current partial trace must be a prefix of a
/** @returns whether the current partial trace is feasible. */
bool ModelChecker::isfeasible() {
- return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
+ return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
}
/** Returns whether the current completed trace is feasible. */
int tid = id_to_int(act->get_tid());
ModelAction *lastread = get_last_action(tid);
lastread->process_rmw(act);
- if (act->is_rmw())
+ if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
+ mo_graph->commitChanges();
+ }
return lastread;
}
/**
- * Checks whether a thread has read from the same write for too many times.
- * @todo This may be more subtle than this code segment addresses at this
- * point... Potential problems to ponder and fix:
- * (1) What if the reads_from set keeps changing such that there is no common
- * write?
- * (2) What if the problem is that the other writes would break modification
- * order.
+ * Checks whether a thread has read from the same write for too many times
+ * without seeing the effects of a later write.
+ *
+ * Basic idea:
+ * 1) there must a different write that we could read from that would satisfy the modification order,
+ * 2) we must have read from the same value in excess of maxreads times, and
+ * 3) that other write must have been in the reads_from set for maxreads times.
+ *
+ * If so, we decide that the execution is no longer feasible.
*/
void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
if (params.maxreads != 0) {
if (curr->get_node()->get_read_from_size() <= 1)
return;
+ //Must make sure that execution is currently feasible... We could
+ //accidentally clear by rolling back
+ if (!isfeasible())
+ return;
+
std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
int tid = id_to_int(curr->get_tid());
action_list_t::reverse_iterator rit = list->rbegin();
/* Skip past curr */
- if (!already_added) {
+ if (already_added) {
for (; (*rit) != curr; rit++)
;
/* go past curr now */
rit++;
}
+ action_list_t::reverse_iterator ritcopy=rit;
+ //See if we have enough reads from the same value
int count=0;
- for (; rit != list->rend(); rit++) {
+ for (; count < params.maxreads; rit++,count++) {
+ if (rit==list->rend())
+ return;
ModelAction *act = *rit;
if (!act->is_read())
return;
return;
if (act->get_node()->get_read_from_size() <= 1)
return;
- count++;
- if (count >= params.maxreads) {
- /* We've read from the same write for too many times */
+ }
+
+ for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
+ //Get write
+ const ModelAction * write=curr->get_node()->get_read_from_at(i);
+ //Need a different write
+ if (write==curr->get_reads_from())
+ continue;
+
+ /* Test to see whether this is a feasible write to read from*/
+ r_modification_order(curr, write);
+ bool feasiblereadfrom=isfeasible();
+ mo_graph->rollbackChanges();
+
+ if (!feasiblereadfrom)
+ continue;
+ rit=ritcopy;
+
+ bool feasiblewrite=true;
+ //new we need to see if this write works for everyone
+
+ for (int loop=count;loop>0;loop--,rit++) {
+ ModelAction *act=*rit;
+ bool foundvalue=false;
+ for(int j=0;j<act->get_node()->get_read_from_size();j++) {
+ if (act->get_node()->get_read_from_at(i)==write) {
+ foundvalue=true;
+ break;
+ }
+ }
+ if (!foundvalue) {
+ feasiblewrite=false;
+ break;
+ }
+ }
+ if (feasiblewrite) {
too_many_reads = true;
+ return;
}
}
}
/* Include at most one act per-thread that "happens before" curr */
if (act->happens_before(curr)) {
- if (act->is_read())
+ /*
+ * Note: if act is RMW, just add edge:
+ * act --mo--> curr
+ * The following edge should be handled elsewhere:
+ * readfrom(act) --mo--> act
+ */
+ if (act->is_write()) {
+ //RMW shouldn't have an edge to themselves
+ if (act!=curr)
+ mo_graph->addEdge(act, curr);
+ } else if (act->is_read() && act->get_reads_from() != NULL)
mo_graph->addEdge(act->get_reads_from(), curr);
- else
- mo_graph->addEdge(act, curr);
added = true;
break;
} else if (act->is_read() && !act->is_synchronizing(curr) &&
=>
that read could potentially read from our write.
*/
- if (act->get_node()->add_future_value(curr->get_value()) &&
+ if (isfeasible() && act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
(!priv->next_backtrack || *act > *priv->next_backtrack))
priv->next_backtrack = act;
}
if (write->get_node()->get_promise(i)) {
ModelAction *read = promise->get_action();
read->read_from(write);
+ if (read->is_rmw()) {
+ mo_graph->addRMWEdge(write, read);
+ }
r_modification_order(read, write);
post_r_modification_order(read, write);
promises->erase(promises->begin() + promise_index);
continue;
/* Don't consider more than one seq_cst write if we are a seq_cst read. */
- if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
+ if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
DEBUG("Adding action to may_read_from:\n");
if (DBG_ENABLED()) {
act->print();
projects / c11tester.git / blobdiff