ModelChecker::ModelChecker(struct model_params params) :
/* Initialize default scheduler */
scheduler(new Scheduler()),
- /* First thread created will have id INITIAL_THREAD_ID */
- next_thread_id(INITIAL_THREAD_ID),
- used_sequence_numbers(0),
num_executions(0),
params(params),
- current_action(NULL),
diverge(NULL),
- nextThread(NULL),
action_trace(new action_list_t()),
thread_map(new HashTable<int, Thread *, int>()),
obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
thrd_last_action(new std::vector<ModelAction *>(1)),
node_stack(new NodeStack()),
- next_backtrack(NULL),
mo_graph(new CycleGraph()),
failed_promise(false),
+ too_many_reads(false),
asserted(false)
{
+ /* Allocate this "size" on the snapshotting heap */
+ priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
+ /* First thread created will have id INITIAL_THREAD_ID */
+ priv->next_thread_id = INITIAL_THREAD_ID;
+
+ lazy_sync_size = &priv->lazy_sync_size;
}
/** @brief Destructor */
{
DEBUG("+++ Resetting to initial state +++\n");
node_stack->reset_execution();
- current_action = NULL;
- next_thread_id = INITIAL_THREAD_ID;
- used_sequence_numbers = 0;
- nextThread = NULL;
- next_backtrack = NULL;
failed_promise = false;
+ too_many_reads = false;
reset_asserted();
snapshotObject->backTrackBeforeStep(0);
}
/** @returns a thread ID for a new Thread */
thread_id_t ModelChecker::get_next_id()
{
- return next_thread_id++;
+ return priv->next_thread_id++;
}
/** @returns the number of user threads created during this execution */
int ModelChecker::get_num_threads()
{
- return next_thread_id;
+ return priv->next_thread_id;
}
/** @returns a sequence number for a new ModelAction */
modelclock_t ModelChecker::get_next_seq_num()
{
- return ++used_sequence_numbers;
+ return ++priv->used_sequence_numbers;
}
/**
- * 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;
return;
/* Cache the latest backtracking point */
- if (!next_backtrack || *prev > *next_backtrack)
- next_backtrack = prev;
+ if (!priv->next_backtrack || *prev > *priv->next_backtrack)
+ priv->next_backtrack = prev;
/* If this is a new backtracking point, mark the tree */
if (!node->set_backtrack(t->get_id()))
*/
ModelAction * ModelChecker::get_next_backtrack()
{
- ModelAction *next = next_backtrack;
- next_backtrack = NULL;
+ ModelAction *next = priv->next_backtrack;
+ priv->next_backtrack = 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();
+ curr->read_from(NULL);
+ Promise *valuepromise = new Promise(curr, value);
+ 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
*/
Thread * ModelChecker::check_current_action(ModelAction *curr)
{
- bool already_added = false;
+ bool second_part_of_rmw = false;
ASSERT(curr);
if (curr->is_rmwc() || curr->is_rmw()) {
ModelAction *tmp = process_rmw(curr);
- already_added = true;
+ second_part_of_rmw = true;
delete curr;
curr = tmp;
} else {
}
}
- /* 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) {
+ break;
+ }
+ case 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) {
+ break;
+ }
+ case THREAD_FINISH: {
Thread *th = get_thread(curr->get_tid());
while (!th->wait_list_empty()) {
Thread *wake = th->pop_wait_list();
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;
+ }
- /* Assign reads_from values */
Thread *th = get_thread(curr->get_tid());
- uint64_t value = VALUE_NONE;
+
bool updated = false;
if (curr->is_read()) {
- 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 (r_modification_order(curr,reads_from))
- updated = true;
- } 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);
- }
- } else if (curr->is_write()) {
- if (w_modification_order(curr))
- updated = true;
- if (resolve_promises(curr))
- updated = true;
+ updated=process_read(curr, th, second_part_of_rmw);
+ }
+
+ 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();
+ th->set_return_value(VALUE_NONE);
}
if (updated)
resolve_release_sequences(curr->get_location());
- th->set_return_value(value);
-
/* Add action to list. */
- if (!already_added)
+ 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 (!next_backtrack || *curr > *next_backtrack)
- 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();
- else
- return get_next_replay_thread();
+ return get_next_thread(curr);
}
/** @returns whether the current partial trace must be a prefix of a
* feasible trace. */
-
bool ModelChecker::isfeasibleprefix() {
- return promises->size()==0;
+ return promises->size() == 0 && *lazy_sync_size == 0;
}
/** @returns whether the current partial trace is feasible. */
bool ModelChecker::isfeasible() {
- return !mo_graph->checkForCycles() && !failed_promise;
+ return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
}
/** Returns whether the current completed trace is feasible. */
return lastread;
}
+/**
+ * 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());
+
+ /* Skip checks */
+ if ((int)thrd_lists->size() <= tid)
+ return;
+
+ action_list_t *list = &(*thrd_lists)[tid];
+
+ action_list_t::reverse_iterator rit = list->rbegin();
+ /* Skip past curr */
+ 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 (; count < params.maxreads; rit++,count++) {
+ if (rit==list->rend())
+ return;
+ ModelAction *act = *rit;
+ if (!act->is_read())
+ return;
+ if (act->get_reads_from() != curr->get_reads_from())
+ return;
+ if (act->get_node()->get_read_from_size() <= 1)
+ return;
+ }
+
+ 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;
+ }
+ }
+ }
+}
+
/**
* Updates the mo_graph with the constraints imposed from the current read.
* @param curr The current action. Must be a read.
/* Include at most one act per-thread that "happens before" curr */
if (act->happens_before(curr)) {
- if (act->is_read())
- mo_graph->addEdge(act->get_reads_from(), curr);
- else
+ /*
+ * 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())
mo_graph->addEdge(act, curr);
+ else if (act->is_read() && act->get_reads_from() != NULL)
+ mo_graph->addEdge(act->get_reads_from(), 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()) &&
- (!next_backtrack || *act > *next_backtrack))
- next_backtrack = act;
+ (!priv->next_backtrack || *act > *priv->next_backtrack))
+ priv->next_backtrack = act;
}
}
}
if (rf->is_release())
release_heads->push_back(rf);
if (rf->is_rmw()) {
- if (rf->is_acquire())
+ /* We need a RMW action that is both an acquire and release to stop */
+ /** @todo Need to be smarter here... In the linux lock
+ * example, this will run to the beginning of the program for
+ * every acquire. */
+ if (rf->is_acquire() && rf->is_release())
return true; /* complete */
return release_seq_head(rf->get_reads_from(), release_heads);
}
std::list<ModelAction *> *list;
list = lazy_sync_with_release->get_safe_ptr(act->get_location());
list->push_back(act);
+ (*lazy_sync_size)++;
}
}
propagate->synchronize_with(act);
}
}
- if (complete)
+ if (complete) {
it = list->erase(it);
- else
+ (*lazy_sync_size)--;
+ } else
it++;
}
std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
if (tid >= (int)vec->size())
- vec->resize(next_thread_id);
+ vec->resize(priv->next_thread_id);
(*vec)[tid].push_back(act);
if ((int)thrd_last_action->size() <= tid)
curr = thread_current();
if (curr) {
if (curr->get_state() == THREAD_READY) {
- ASSERT(current_action);
- nextThread = check_current_action(current_action);
- current_action = NULL;
+ ASSERT(priv->current_action);
+ priv->nextThread = check_current_action(priv->current_action);
+ priv->current_action = NULL;
if (!curr->is_blocked() && !curr->is_complete())
scheduler->add_thread(curr);
} else {
ASSERT(false);
}
}
- next = scheduler->next_thread(nextThread);
+ next = scheduler->next_thread(priv->nextThread);
/* Infeasible -> don't take any more steps */
if (!isfeasible())
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