From 8e649bb08299bf12cc4e50ffd5f956a4faf32f8f Mon Sep 17 00:00:00 2001
From: Brian Norris <banorris@uci.edu>
Date: Tue, 10 Apr 2012 14:09:42 -0700
Subject: [PATCH] threads_internal: add 'thread_switch_to_master()' internally

In progress: moving more model-checking/thread actions so that they are
performed only by a system thread, not by the user code.

For now, we replace our uses of thread_yield() (which simply switched to the
next user thread) while thread_switch_to_master() (which will later perform
intermediate actions before choosing the next user thread).

Also, we can begin creating internal and external interfaces in
threads_indernal.h and libthreads.h, respectively.
---
 Makefile           |  2 +-
 libatomic.cc       |  6 +++---
 libthreads.cc      | 25 ++++++++++++++++---------
 threads_internal.h |  8 ++++++++
 4 files changed, 28 insertions(+), 13 deletions(-)
 create mode 100644 threads_internal.h

diff --git a/Makefile b/Makefile
index 327bbb5..7a442bd 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 CC=g++
 BIN=libthreads
 SOURCE=libthreads.cc schedule.cc libatomic.cc userprog.c model.cc malloc.c
-HEADERS=libthreads.h schedule.h common.h libatomic.h model.h
+HEADERS=libthreads.h schedule.h common.h libatomic.h model.h threads_internal.h
 FLAGS=-Wall -ldl
 
 all: ${BIN}
diff --git a/libatomic.cc b/libatomic.cc
index a00838e..daf058a 100644
--- a/libatomic.cc
+++ b/libatomic.cc
@@ -1,13 +1,13 @@
 #include "libatomic.h"
-#include "libthreads.h"
+#include "threads_internal.h"
 
 void atomic_store_explicit(struct atomic_object *obj, int value, memory_order order)
 {
-	thread_yield();
+	thread_switch_to_master();
 }
 
 int atomic_load_explicit(struct atomic_object *obj, memory_order order)
 {
-	thread_yield();
+	thread_switch_to_master();
 	return 0;
 }
diff --git a/libthreads.cc b/libthreads.cc
index c0439ff..42e9198 100644
--- a/libthreads.cc
+++ b/libthreads.cc
@@ -4,6 +4,7 @@
 #include "libthreads.h"
 #include "schedule.h"
 #include "common.h"
+#include "threads_internal.h"
 
 /* global "model" object */
 #include "model.h"
@@ -97,6 +98,17 @@ static void thread_wait_finish(void)
 	while (!thread_system_next());
 }
 
+int thread_switch_to_master()
+{
+	struct thread *old, *next;
+
+	DBG();
+	old = thread_current();
+	old->state = THREAD_READY;
+	next = model->system_thread;
+	return thread_swap(old, next);
+}
+
 /*
  * User program API functions
  */
@@ -126,19 +138,14 @@ int thread_create(struct thread *t, void (*start_routine)(), void *arg)
 
 void thread_join(struct thread *t)
 {
-	while (t->state != THREAD_COMPLETED)
-		thread_yield();
+	int ret = 0;
+	while (t->state != THREAD_COMPLETED && !ret)
+		ret = thread_switch_to_master();
 }
 
 int thread_yield(void)
 {
-	struct thread *old, *next;
-
-	DBG();
-	old = thread_current();
-	old->state = THREAD_READY;
-	next = model->system_thread;
-	return thread_swap(old, next);
+	return thread_switch_to_master();
 }
 
 struct thread *thread_current(void)
diff --git a/threads_internal.h b/threads_internal.h
new file mode 100644
index 0000000..37b446c
--- /dev/null
+++ b/threads_internal.h
@@ -0,0 +1,8 @@
+#ifndef __THREADS_INTERNAL_H__
+#define __THREADS_INTERNAL_H__
+
+#include "libthreads.h"
+
+int thread_switch_to_master();
+
+#endif /* __THREADS_INTERNAL_H__ */
-- 
2.34.1