X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=blobdiff_plain;f=model.cc;h=3262f5e55caf992397d9134f24f2bba325cc4e87;hp=f447c1dfa50e98139b4b1b30a7cb5d9d5a6a5060;hb=805a3e1b51dacac117b394f1c1b0220e3ae9f5e4;hpb=996d51da9229031b9d7841c2f3d3b7629db2cba9

diff --git a/model.cc b/model.cc
index f447c1df..3262f5e5 100644
--- a/model.cc
+++ b/model.cc
@@ -2,91 +2,147 @@
 
 #include "model.h"
 #include "action.h"
-#include "tree.h"
+#include "nodestack.h"
 #include "schedule.h"
+#include "snapshot-interface.h"
 #include "common.h"
+#include "clockvector.h"
+#include "cyclegraph.h"
 
 #define INITIAL_THREAD_ID	0
 
 ModelChecker *model;
 
+/** @brief Constructor */
 ModelChecker::ModelChecker()
-{
-	/* First thread created will have id (INITIAL_THREAD_ID + 1) */
-	this->used_thread_id = INITIAL_THREAD_ID;
+	:
 	/* Initialize default scheduler */
-	this->scheduler = new Scheduler();
-
-	num_executions = 0;
-	this->current_action = NULL;
-	this->exploring = NULL;
-	this->nextThread = THREAD_ID_T_NONE;
-
-	rootNode = new TreeNode(NULL);
-	currentNode = rootNode;
-	action_trace = new action_list_t();
+	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),
+	current_action(NULL),
+	diverge(NULL),
+	nextThread(THREAD_ID_T_NONE),
+	action_trace(new action_list_t()),
+	thread_map(new std::map<int, Thread *>),
+	obj_map(new std::map<const void *, action_list_t>()),
+	obj_thrd_map(new std::map<void *, std::vector<action_list_t> >()),
+	thrd_last_action(new std::vector<ModelAction *>(1)),
+	node_stack(new NodeStack()),
+	next_backtrack(NULL),
+	cyclegraph(new CycleGraph())
+{
 }
 
+/** @brief Destructor */
 ModelChecker::~ModelChecker()
 {
+	std::map<int, Thread *>::iterator it;
+	for (it = thread_map->begin(); it != thread_map->end(); it++)
+		delete (*it).second;
+	delete thread_map;
+
+	delete obj_thrd_map;
+	delete obj_map;
 	delete action_trace;
-	delete this->scheduler;
-	delete rootNode;
+	delete thrd_last_action;
+	delete node_stack;
+	delete scheduler;
+	delete cyclegraph;
 }
 
+/**
+ * Restores user program to initial state and resets all model-checker data
+ * structures.
+ */
 void ModelChecker::reset_to_initial_state()
 {
 	DEBUG("+++ Resetting to initial state +++\n");
-	std::map<thread_id_t, class Thread *>::iterator it;
-	for (it = thread_map.begin(); it != thread_map.end(); it++) {
-		delete (*it).second;
-	}
-	thread_map.clear();
-	action_trace = new action_list_t();
-	currentNode = rootNode;
+	node_stack->reset_execution();
 	current_action = NULL;
-	used_thread_id = INITIAL_THREAD_ID;
-	/* scheduler reset ? */
+	next_thread_id = INITIAL_THREAD_ID;
+	used_sequence_numbers = 0;
+	nextThread = 0;
+	next_backtrack = NULL;
+	snapshotObject->backTrackBeforeStep(0);
 }
 
-int ModelChecker::get_next_id()
+/** @returns a thread ID for a new Thread */
+thread_id_t ModelChecker::get_next_id()
 {
-	return ++used_thread_id;
+	return next_thread_id++;
 }
 
+/** @returns the number of user threads created during this execution */
+int ModelChecker::get_num_threads()
+{
+	return next_thread_id;
+}
+
+/** @returns a sequence number for a new ModelAction */
+modelclock_t ModelChecker::get_next_seq_num()
+{
+	return ++used_sequence_numbers;
+}
+
+/**
+ * Performs the "scheduling" for the model-checker. That is, it checks if the
+ * model-checker has selected a "next thread to run" and returns it, if
+ * available. This function should be called from the Scheduler routine, where
+ * the Scheduler falls back to a default scheduling routine if needed.
+ *
+ * @return The next thread chosen by the model-checker. If the model-checker
+ * makes no selection, retuns NULL.
+ */
 Thread * ModelChecker::schedule_next_thread()
 {
 	Thread *t;
 	if (nextThread == THREAD_ID_T_NONE)
 		return NULL;
-	t = thread_map[nextThread];
-	if (t == NULL)
-		DEBUG("*** error: thread not in thread_map: id = %d\n", nextThread);
+	t = (*thread_map)[id_to_int(nextThread)];
+
+	ASSERT(t != NULL);
+
 	return t;
 }
 
-/*
- * get_next_replay_thread() - Choose the next thread in the replay sequence
+/**
+ * Choose the next thread in the replay sequence.
  *
- * If we've reached the 'diverge' point, then we pick a thread from the
- *   backtracking set.
- * Otherwise, we simply return the next thread in the sequence.
+ * 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.
  */
 thread_id_t ModelChecker::get_next_replay_thread()
 {
 	ModelAction *next;
 	thread_id_t tid;
 
-	next = exploring->get_state();
-
-	if (next == exploring->get_diverge()) {
-		TreeNode *node = next->get_node();
+	/* Have we completed exploring the preselected path? */
+	if (diverge == NULL)
+		return THREAD_ID_T_NONE;
 
-		/* Reached divergence point; discard our current 'exploring' */
-		DEBUG("*** Discard 'Backtrack' object ***\n");
-		tid = node->getNextBacktrack();
-		delete exploring;
-		exploring = NULL;
+	/* Else, we are trying to replay an execution */
+	next = node_stack->get_next()->get_action();
+
+	if (next == diverge) {
+		Node *nextnode = next->get_node();
+		/* Reached divergence point */
+		if (nextnode->increment_read_from()) {
+			/* The next node will read from a different value */
+			tid = next->get_tid();
+			node_stack->pop_restofstack(2);
+		} else {
+			/* Make a different thread execute for next step */
+			Node *node = nextnode->get_parent();
+			tid = node->get_next_backtrack();
+			node_stack->pop_restofstack(1);
+		}
+		DEBUG("*** Divergence point ***\n");
+		diverge = NULL;
 	} else {
 		tid = next->get_tid();
 	}
@@ -94,28 +150,31 @@ thread_id_t ModelChecker::get_next_replay_thread()
 	return tid;
 }
 
-thread_id_t ModelChecker::advance_backtracking_state()
+/**
+ * Queries the model-checker for more executions to explore and, if one
+ * exists, resets the model-checker state to execute a new execution.
+ *
+ * @return If there are more executions to explore, return true. Otherwise,
+ * return false.
+ */
+bool ModelChecker::next_execution()
 {
-	/* Have we completed exploring the preselected path? */
-	if (exploring == NULL)
-		return THREAD_ID_T_NONE;
+	DBG();
 
-	/* Else, we are trying to replay an execution */
-	exploring->advance_state();
-	if (exploring->get_state() == NULL)
-		DEBUG("*** error: reached end of backtrack trace\n");
+	num_executions++;
 
-	return get_next_replay_thread();
-}
+	if (isfeasible() || DBG_ENABLED())
+		print_summary();
 
-bool ModelChecker::next_execution()
-{
-	num_executions++;
-	print_summary();
-	if ((exploring = model->get_next_backtrack()) == NULL)
+	if ((diverge = model->get_next_backtrack()) == NULL)
 		return false;
+
+	if (DBG_ENABLED()) {
+		printf("Next execution will diverge at:\n");
+		diverge->print();
+	}
+
 	model->reset_to_initial_state();
-	nextThread = get_next_replay_thread();
 	return true;
 }
 
@@ -124,20 +183,19 @@ ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 	action_type type = act->get_type();
 
 	switch (type) {
-		case THREAD_CREATE:
-		case THREAD_YIELD:
-		case THREAD_JOIN:
-			return NULL;
 		case ATOMIC_READ:
 		case ATOMIC_WRITE:
-		default:
+		case ATOMIC_RMW:
 			break;
+		default:
+			return NULL;
 	}
 	/* linear search: from most recent to oldest */
+	action_list_t *list = &(*obj_map)[act->get_location()];
 	action_list_t::reverse_iterator rit;
-	for (rit = action_trace->rbegin(); rit != action_trace->rend(); rit++) {
+	for (rit = list->rbegin(); rit != list->rend(); rit++) {
 		ModelAction *prev = *rit;
-		if (act->is_dependent(prev))
+		if (act->is_synchronizing(prev))
 			return prev;
 	}
 	return NULL;
@@ -146,191 +204,405 @@ ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 void ModelChecker::set_backtracking(ModelAction *act)
 {
 	ModelAction *prev;
-	TreeNode *node;
+	Node *node;
+	Thread *t = get_thread(act->get_tid());
 
 	prev = get_last_conflict(act);
 	if (prev == NULL)
 		return;
 
-	node = prev->get_node();
+	node = prev->get_node()->get_parent();
+
+	while (!node->is_enabled(t))
+		t = t->get_parent();
 
 	/* Check if this has been explored already */
-	if (node->hasBeenExplored(act->get_tid()))
+	if (node->has_been_explored(t->get_id()))
 		return;
+
+	/* Cache the latest backtracking point */
+	if (!next_backtrack || *prev > *next_backtrack)
+		next_backtrack = prev;
+
 	/* If this is a new backtracking point, mark the tree */
-	if (node->setBacktrack(act->get_tid()) != 0)
+	if (!node->set_backtrack(t->get_id()))
 		return;
-
 	DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
-			prev->get_tid(), act->get_tid());
+			prev->get_tid(), t->get_id());
 	if (DBG_ENABLED()) {
 		prev->print();
 		act->print();
 	}
-
-	Backtrack *back = new Backtrack(prev, action_trace);
-	backtrack_list.push_back(back);
 }
 
-Backtrack * ModelChecker::get_next_backtrack()
+/**
+ * Returns last backtracking point. The model checker will explore a different
+ * path for this point in the next execution.
+ * @return The ModelAction at which the next execution should diverge.
+ */
+ModelAction * ModelChecker::get_next_backtrack()
 {
-	Backtrack *next;
-	if (backtrack_list.empty())
-		return NULL;
-	next = backtrack_list.back();
-	backtrack_list.pop_back();
+	ModelAction *next = next_backtrack;
+	next_backtrack = NULL;
 	return next;
 }
 
 void ModelChecker::check_current_action(void)
 {
-	ModelAction *next = this->current_action;
-
-	if (!next) {
+	ModelAction *curr = this->current_action;
+	ModelAction *tmp;
+	current_action = NULL;
+	if (!curr) {
 		DEBUG("trying to push NULL action...\n");
 		return;
 	}
-	current_action = NULL;
-	nextThread = advance_backtracking_state();
-	next->set_node(currentNode);
-	set_backtracking(next);
-	currentNode = currentNode->exploreChild(next->get_tid());
-	this->action_trace->push_back(next);
-}
 
-void ModelChecker::print_summary(void)
-{
-	action_list_t::iterator it;
+	if (curr->is_rmw()) {
+		//We have a RMW action
+		process_rmw(curr);
+		//Force the current thread to continue since the RMW should be atomic
+		nextThread = thread_current()->get_id();
+		delete curr;
+		return;
+	}
 
-	printf("\n");
-	printf("---------------------------------------------------------------------\n");
-	printf("Number of executions: %d\n", num_executions);
-	printf("Total nodes created: %d\n\n", TreeNode::getTotalNodes());
+	tmp = node_stack->explore_action(curr);
+	if (tmp) {
+		/* Discard duplicate ModelAction; use action from NodeStack */
+		delete curr;
+		curr = tmp;
+	} else {
+		/*
+		 * Perform one-time actions when pushing new ModelAction onto
+		 * NodeStack
+		 */
+		curr->create_cv(get_parent_action(curr->get_tid()));
+		/* Build may_read_from set */
+		if (curr->is_read())
+			build_reads_from_past(curr);
+	}
 
-	scheduler->print();
+	/* Assign 'creation' parent */
+	if (curr->get_type() == THREAD_CREATE) {
+		Thread *th = (Thread *)curr->get_location();
+		th->set_creation(curr);
+	}
 
-	printf("Trace:\n\n");
+	/* Is there a better interface for setting the next thread rather
+		 than this field/convoluted approach?  Perhaps like just returning
+		 it or something? */
 
-	for (it = action_trace->begin(); it != action_trace->end(); it++) {
-		DBG();
-		(*it)->print();
+	nextThread = get_next_replay_thread();
+
+	Node *currnode = curr->get_node();
+	Node *parnode = currnode->get_parent();
+
+	if (!parnode->backtrack_empty()||!currnode->readsfrom_empty())
+		if (!next_backtrack || *curr > *next_backtrack)
+			next_backtrack = curr;
+
+	set_backtracking(curr);
+
+	/* Assign reads_from values */
+	/* TODO: perform release/acquire synchronization here; include
+	 * reads_from as ModelAction member? */
+	Thread *th = get_thread(curr->get_tid());
+	uint64_t value = VALUE_NONE;
+	if (curr->is_read()) {
+		const ModelAction *reads_from = curr->get_node()->get_read_from();
+		value = reads_from->get_value();
+		/* Assign reads_from, perform release/acquire synchronization */
+		curr->read_from(reads_from);
+		r_modification_order(curr,reads_from);
+	} else if (curr->is_write()) {
+		w_modification_order(curr);
 	}
-	printf("---------------------------------------------------------------------\n");
+
+	th->set_return_value(value);
+
+	/* Add action to list last.  */
+	add_action_to_lists(curr);
 }
 
-int ModelChecker::add_thread(Thread *t)
-{
-	thread_map[t->get_id()] = t;
-	scheduler->add_thread(t);
-	return 0;
+/** @returns whether the current trace is feasible. */
+bool ModelChecker::isfeasible() {
+	return !cyclegraph->checkForCycles();
 }
 
-void ModelChecker::remove_thread(Thread *t)
-{
-	scheduler->remove_thread(t);
+/** Process a RMW by converting previous read into a RMW. */
+void ModelChecker::process_rmw(ModelAction * act) {
+	int tid = id_to_int(act->get_tid());
+	std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
+	ASSERT(tid < (int) vec->size());
+	ModelAction *lastread=(*vec)[tid].back();
+	lastread->upgrade_rmw(act);
 }
 
-int ModelChecker::switch_to_master(ModelAction *act)
+/**
+ * Updates the cyclegraph with the constraints imposed from the current read.
+ * @param curr The current action. Must be a read.
+ * @param rf The action that curr reads from. Must be a write.
+ */
+void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
+	std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
+	unsigned int i;
+	ASSERT(curr->is_read());
+
+	/* Iterate over all threads */
+	for (i = 0; i < thrd_lists->size(); i++) {
+		/* Iterate over actions in thread, starting from most recent */
+		action_list_t *list = &(*thrd_lists)[i];
+		action_list_t::reverse_iterator rit;
+		for (rit = list->rbegin(); rit != list->rend(); rit++) {
+			ModelAction *act = *rit;
+
+			/* Include at most one act per-thread that "happens before" curr */
+			if (act->happens_before(curr)) {
+				if (act->is_read()) {
+					const ModelAction * prevreadfrom=act->get_reads_from();
+					if (rf!=prevreadfrom)
+						cyclegraph->addEdge(rf, prevreadfrom);
+				} else if (rf!=act) {
+					cyclegraph->addEdge(rf, act);
+				}
+				break;
+			}
+		}
+	}
+}
+
+/**
+ * Updates the cyclegraph with the constraints imposed from the current write.
+ * @param curr The current action. Must be a write.
+ */
+void ModelChecker::w_modification_order(ModelAction * curr) {
+	std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
+	unsigned int i;
+	ASSERT(curr->is_write());
+
+	if (curr->is_seqcst()) {
+		/* We have to at least see the last sequentially consistent write,
+			 so we are initialized. */
+		ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
+		if (last_seq_cst!=NULL)
+			cyclegraph->addEdge(curr, last_seq_cst);
+	}
+
+	/* Iterate over all threads */
+	for (i = 0; i < thrd_lists->size(); i++) {
+		/* Iterate over actions in thread, starting from most recent */
+		action_list_t *list = &(*thrd_lists)[i];
+		action_list_t::reverse_iterator rit;
+		for (rit = list->rbegin(); rit != list->rend(); rit++) {
+			ModelAction *act = *rit;
+
+			/* Include at most one act per-thread that "happens before" curr */
+			if (act->happens_before(curr)) {
+				if (act->is_read()) {
+					cyclegraph->addEdge(curr, act->get_reads_from());
+				} else
+					cyclegraph->addEdge(curr, act);
+				break;
+			}
+		}
+	}
+}
+
+/**
+ * Performs various bookkeeping operations for the current ModelAction. For
+ * instance, adds action to the per-object, per-thread action vector and to the
+ * action trace list of all thread actions.
+ *
+ * @param act is the ModelAction to add.
+ */
+void ModelChecker::add_action_to_lists(ModelAction *act)
 {
-	Thread *old;
+	int tid = id_to_int(act->get_tid());
+	action_trace->push_back(act);
 
-	DBG();
-	old = thread_current();
-	set_current_action(act);
-	old->set_state(THREAD_READY);
-	return Thread::swap(old, get_system_context());
+	(*obj_map)[act->get_location()].push_back(act);
+
+	std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
+	if (tid >= (int)vec->size())
+		vec->resize(next_thread_id);
+	(*vec)[tid].push_back(act);
+
+	if ((int)thrd_last_action->size() <= tid)
+		thrd_last_action->resize(get_num_threads());
+	(*thrd_last_action)[tid] = act;
 }
 
-ModelAction::ModelAction(action_type_t type, memory_order order, void *loc, int value)
+ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 {
-	Thread *t = thread_current();
-	ModelAction *act = this;
-
-	act->type = type;
-	act->order = order;
-	act->location = loc;
-	act->tid = t->get_id();
-	act->value = value;
+	int nthreads = get_num_threads();
+	if ((int)thrd_last_action->size() < nthreads)
+		thrd_last_action->resize(nthreads);
+	return (*thrd_last_action)[id_to_int(tid)];
 }
 
-bool ModelAction::is_read()
+/**
+ * Gets the last memory_order_seq_cst action (in the total global sequence)
+ * performed on a particular object (i.e., memory location).
+ * @param location The object location to check
+ * @return The last seq_cst action performed
+ */
+ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 {
-	return type == ATOMIC_READ;
+	action_list_t *list = &(*obj_map)[location];
+	/* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
+	action_list_t::reverse_iterator rit;
+	for (rit = list->rbegin(); rit != list->rend(); rit++)
+		if ((*rit)->is_write() && (*rit)->is_seqcst())
+			return *rit;
+	return NULL;
 }
 
-bool ModelAction::is_write()
+ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 {
-	return type == ATOMIC_WRITE;
+	ModelAction *parent = get_last_action(tid);
+	if (!parent)
+		parent = get_thread(tid)->get_creation();
+	return parent;
+}
+
+/**
+ * Returns the clock vector for a given thread.
+ * @param tid The thread whose clock vector we want
+ * @return Desired clock vector
+ */
+ClockVector * ModelChecker::get_cv(thread_id_t tid) {
+	return get_parent_action(tid)->get_cv();
 }
 
-bool ModelAction::is_acquire()
+/**
+ * Build up an initial set of all past writes that this 'read' action may read
+ * from. This set is determined by the clock vector's "happens before"
+ * relationship.
+ * @param curr is the current ModelAction that we are exploring; it must be a
+ * 'read' operation.
+ */
+void ModelChecker::build_reads_from_past(ModelAction *curr)
 {
-	switch (order) {
-	case memory_order_acquire:
-	case memory_order_acq_rel:
-	case memory_order_seq_cst:
-		return true;
-	default:
-		return false;
+	std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
+	unsigned int i;
+	ASSERT(curr->is_read());
+
+	ModelAction *last_seq_cst = NULL;
+
+	/* Track whether this object has been initialized */
+	bool initialized = false;
+
+	if (curr->is_seqcst()) {
+		last_seq_cst = get_last_seq_cst(curr->get_location());
+		/* We have to at least see the last sequentially consistent write,
+			 so we are initialized. */
+		if (last_seq_cst != NULL)
+			initialized = true;
+	}
+
+	/* Iterate over all threads */
+	for (i = 0; i < thrd_lists->size(); i++) {
+		/* Iterate over actions in thread, starting from most recent */
+		action_list_t *list = &(*thrd_lists)[i];
+		action_list_t::reverse_iterator rit;
+		for (rit = list->rbegin(); rit != list->rend(); rit++) {
+			ModelAction *act = *rit;
+
+			/* Only consider 'write' actions */
+			if (!act->is_write())
+				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) {
+				DEBUG("Adding action to may_read_from:\n");
+				if (DBG_ENABLED()) {
+					act->print();
+					curr->print();
+				}
+				curr->get_node()->add_read_from(act);
+			}
+
+			/* Include at most one act per-thread that "happens before" curr */
+			if (act->happens_before(curr)) {
+				initialized = true;
+				break;
+			}
+		}
+	}
+
+	if (!initialized) {
+		/* TODO: need a more informative way of reporting errors */
+		printf("ERROR: may read from uninitialized atomic\n");
 	}
+	
+	if (DBG_ENABLED() || !initialized) {
+		printf("Reached read action:\n");
+		curr->print();
+		printf("Printing may_read_from\n");
+		curr->get_node()->print_may_read_from();
+		printf("End printing may_read_from\n");
+	}
+	
+	ASSERT(initialized);
 }
 
-bool ModelAction::is_release()
+static void print_list(action_list_t *list)
 {
-	switch (order) {
-	case memory_order_release:
-	case memory_order_acq_rel:
-	case memory_order_seq_cst:
-		return true;
-	default:
-		return false;
+	action_list_t::iterator it;
+
+	printf("---------------------------------------------------------------------\n");
+	printf("Trace:\n");
+
+	for (it = list->begin(); it != list->end(); it++) {
+		(*it)->print();
 	}
+	printf("---------------------------------------------------------------------\n");
 }
 
-bool ModelAction::same_var(ModelAction *act)
+void ModelChecker::print_summary(void)
 {
-	return location == act->location;
+	printf("\n");
+	printf("Number of executions: %d\n", num_executions);
+	printf("Total nodes created: %d\n", node_stack->get_total_nodes());
+
+	scheduler->print();
+
+	if (!isfeasible())
+		printf("INFEASIBLE EXECUTION!\n");
+	print_list(action_trace);
+	printf("\n");
 }
 
-bool ModelAction::same_thread(ModelAction *act)
+int ModelChecker::add_thread(Thread *t)
 {
-	return tid == act->tid;
+	(*thread_map)[id_to_int(t->get_id())] = t;
+	scheduler->add_thread(t);
+	return 0;
 }
 
-bool ModelAction::is_dependent(ModelAction *act)
+void ModelChecker::remove_thread(Thread *t)
 {
-	if (!is_read() && !is_write())
-		return false;
-	if (!act->is_read() && !act->is_write())
-		return false;
-	if (same_var(act) && !same_thread(act) &&
-			(is_write() || act->is_write()))
-		return true;
-	return false;
+	scheduler->remove_thread(t);
 }
 
-void ModelAction::print(void)
+/**
+ * Switch from a user-context to the "master thread" context (a.k.a. system
+ * context). This switch is made with the intention of exploring a particular
+ * model-checking action (described by a ModelAction object). Must be called
+ * from a user-thread context.
+ * @param act The current action that will be explored. May be NULL, although
+ * there is little reason to switch to the model-checker without an action to
+ * explore (note: act == NULL is sometimes used as a hack to allow a thread to
+ * yield control without performing any progress; see thrd_join()).
+ * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
+ */
+int ModelChecker::switch_to_master(ModelAction *act)
 {
-	const char *type_str;
-	switch (this->type) {
-	case THREAD_CREATE:
-		type_str = "thread create";
-		break;
-	case THREAD_YIELD:
-		type_str = "thread yield";
-		break;
-	case THREAD_JOIN:
-		type_str = "thread join";
-		break;
-	case ATOMIC_READ:
-		type_str = "atomic read";
-		break;
-	case ATOMIC_WRITE:
-		type_str = "atomic write";
-		break;
-	default:
-		type_str = "unknown type";
-	}
+	Thread *old;
 
-	printf("Thread: %d\tAction: %s\tMO: %d\tLoc: %#014zx\tValue: %d\n", tid, type_str, order, (size_t)location, value);
+	DBG();
+	old = thread_current();
+	set_current_action(act);
+	old->set_state(THREAD_READY);
+	return Thread::swap(old, get_system_context());
 }