From: Brian Norris <banorris@uci.edu>
Date: Thu, 26 Apr 2012 23:52:20 +0000 (-0700)
Subject: demote 'system_thread' to just 'system_context'
X-Git-Tag: pldi2013~490
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=8a7dd35db7542ad66f87060cf637172249494e47;p=model-checker.git

demote 'system_thread' to just 'system_context'

I don't need the extra 'class Thread' metadata for the ModelChecker 'system
thread,' and the dual use of class Thread for both system and user threads was
causing problems. So I separate them: class Thread is used only for user
threads. This changes a few interfaces throughout the code.
---

diff --git a/model.cc b/model.cc
index 19570ff..f1bc320 100644
--- a/model.cc
+++ b/model.cc
@@ -50,11 +50,6 @@ int ModelChecker::get_next_id()
 	return ++used_thread_id;
 }
 
-void ModelChecker::add_system_thread(Thread *t)
-{
-	this->system_thread = t;
-}
-
 Thread * ModelChecker::schedule_next_thread()
 {
 	Thread *t;
@@ -239,14 +234,13 @@ void ModelChecker::remove_thread(Thread *t)
 
 int ModelChecker::switch_to_master(ModelAction *act)
 {
-	Thread *old, *next;
+	Thread *old;
 
 	DBG();
 	old = thread_current();
 	set_current_action(act);
 	old->set_state(THREAD_READY);
-	next = system_thread;
-	return old->swap(next);
+	return Thread::swap(old, get_system_context());
 }
 
 ModelAction::ModelAction(action_type_t type, memory_order order, void *loc, int value)
diff --git a/model.h b/model.h
index aac968a..ad8760a 100644
--- a/model.h
+++ b/model.h
@@ -4,6 +4,7 @@
 #include <list>
 #include <map>
 #include <cstddef>
+#include <ucontext.h>
 
 #include "schedule.h"
 #include "libthreads.h"
@@ -69,9 +70,9 @@ public:
 	ModelChecker();
 	~ModelChecker();
 	class Scheduler *scheduler;
-	Thread *system_thread;
 
-	void add_system_thread(Thread *t);
+	void set_system_context(ucontext_t *ctxt) { system_context = ctxt; }
+	ucontext_t * get_system_context(void) { return system_context; }
 
 	void set_current_action(ModelAction *act) { current_action = act; }
 	void check_current_action(void);
@@ -102,6 +103,7 @@ private:
 	Backtrack *exploring;
 	thread_id_t nextThread;
 
+	ucontext_t *system_context;
 	action_list_t *action_trace;
 	std::map<thread_id_t, class Thread *> thread_map;
 	class TreeNode *rootNode, *currentNode;
diff --git a/threads.cc b/threads.cc
index 917090f..dc7202e 100644
--- a/threads.cc
+++ b/threads.cc
@@ -42,15 +42,20 @@ int Thread::create_context()
 	context.uc_stack.ss_sp = stack;
 	context.uc_stack.ss_size = STACK_SIZE;
 	context.uc_stack.ss_flags = 0;
-	context.uc_link = &model->system_thread->context;
+	context.uc_link = model->get_system_context();
 	makecontext(&context, start_routine, 1, arg);
 
 	return 0;
 }
 
-int Thread::swap(Thread *t)
+int Thread::swap(Thread *t, ucontext_t *ctxt)
 {
-	return swapcontext(&this->context, &t->context);
+	return swapcontext(&t->context, ctxt);
+}
+
+int Thread::swap(ucontext_t *ctxt, Thread *t)
+{
+	return swapcontext(ctxt, &t->context);
 }
 
 void Thread::complete()
@@ -99,7 +104,7 @@ Thread::Thread(thrd_t *t) {
 	state = THREAD_CREATED;
 	id = model->get_next_id();
 	*user_thread = id;
-	model->add_system_thread(this);
+	model->set_system_context(&context);
 }
 
 Thread::~Thread()
@@ -137,7 +142,7 @@ static int thread_system_next(void)
 	DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
 	if (!next)
 		return 1;
-	return model->system_thread->swap(next);
+	return Thread::swap(model->get_system_context(), next);
 }
 
 static void thread_wait_finish(void)
@@ -153,12 +158,15 @@ static void thread_wait_finish(void)
  */
 int main()
 {
-	thrd_t user_thread, main_thread;
-	Thread *th;
+	thrd_t user_thread;
+	ucontext_t main_context;
 
 	model = new ModelChecker();
 
-	th = new Thread(&main_thread);
+	if (getcontext(&main_context))
+		return 1;
+
+	model->set_system_context(&main_context);
 
 	do {
 		/* Start user program */
@@ -168,7 +176,6 @@ int main()
 		thread_wait_finish();
 	} while (model->next_execution());
 
-	delete th;
 	delete model;
 
 	DEBUG("Exiting\n");
diff --git a/threads.h b/threads.h
index 44e1013..490081a 100644
--- a/threads.h
+++ b/threads.h
@@ -22,7 +22,9 @@ public:
 	Thread(thrd_t *t);
 	~Thread();
 	void complete();
-	int swap(Thread *t);
+
+	static int swap(ucontext_t *ctxt, Thread *t);
+	static int swap(Thread *t, ucontext_t *ctxt);
 
 	thread_state get_state() { return state; }
 	void set_state(thread_state s) { state = s; }