various tweaks.

src/libthread/create.c

@@ -2,6 +2,8 @@
 
 Pqueue _threadpq;
 
+int _threadmultiproc;
+
 static int nextID(void);
 
 /*
@@ -81,6 +83,14 @@ procrfork(void (*f)(void *), void *arg, uint stacksize, int rforkflag)
 int
 proccreate(void (*f)(void*), void *arg, uint stacksize)
 {
+	Proc *p;
+
+	p = _threadgetproc();
+	if(p->idle){
+		werrstr("cannot create procs once there is an idle thread");
+		return -1;
+	}
+	_threadmultiproc = 1;
 	return procrfork(f, arg, stacksize, 0);
 }
 
@@ -110,6 +120,20 @@ threadcreate(void (*f)(void *arg), void *arg, uint stacksize)
 	return newthread(_threadgetproc(), f, arg, stacksize, nil, threadgetgrp());
 }
 
+int
+threadcreateidle(void (*f)(void *arg), void *arg, uint stacksize)
+{
+	int id;
+
+	if(_threadmultiproc){
+		werrstr("cannot have idle thread in multi-proc program");
+		return -1;
+	}
+	id = newthread(_threadgetproc(), f, arg, stacksize, nil, threadgetgrp());
+	_threadidle();
+	return id;
+}
+
 /*
  * Create and initialize a new Proc structure with a single Thread
  * running inside it.  Add the Proc to the global process list.

src/libthread/exit.c

@@ -12,6 +12,8 @@ threadexits(char *exitstr)
 
 	p = _threadgetproc();
 	t = p->thread;
+	if(t == p->idle)
+		p->idle = nil;
 	t->moribund = 1;
 	_threaddebug(DBGSCHED, "threadexits %s", exitstr);
 	if(exitstr==nil)

src/libthread/sched.c

@@ -93,12 +93,21 @@ runthread(Proc *p)
 	Thread *t;
 	Tqueue *q;
 
-	if(p->nthreads==0)
+	if(p->nthreads==0 || (p->nthreads==1 && p->idle))
 		return nil;
 	q = &p->ready;
 	lock(&p->readylock);
 	if(q->head == nil){
 		q->asleep = 1;
+		if(p->idle){
+			if(p->idle->state != Ready){
+				fprint(2, "everyone is asleep\n");
+				exits("everyone is asleep");
+			}
+			unlock(&p->readylock);
+			return p->idle;
+		}
+
 		_threaddebug(DBGSCHED, "sleeping for more work (%d threads)", p->nthreads);
 		unlock(&p->readylock);
 		while(rendezvous((ulong)q, 0) == ~0){
@@ -167,6 +176,9 @@ _threadready(Thread *t)
 {
 	Tqueue *q;
 
+	if(t == t->proc->idle)
+		return;
+
 	assert(t->state == Ready);
 	_threaddebug(DBGSCHED, "readying %d.%d", t->proc->pid, t->id);
 	q = &t->proc->ready;
@@ -190,6 +202,25 @@ _threadready(Thread *t)
 		unlock(&t->proc->readylock);
 }
 
+void
+_threadidle(void)
+{
+	Tqueue *q;
+	Thread *t;
+	Proc *p;
+
+	p = _threadgetproc();
+	q = &p->ready;
+	lock(&p->readylock);
+	assert(q->head);
+	t = q->head;
+	q->head = t->next;
+	if(q->tail == t)
+		q->tail = nil;
+	p->idle = t;
+	unlock(&p->readylock);
+}
+
 void
 yield(void)
 {

src/libthread/threadimpl.h

@@ -115,6 +115,7 @@ struct Proc
 	int		pid;			/* process id */
 	int		splhi;		/* delay notes */
 	Thread	*thread;		/* running thread */
+	Thread	*idle;			/* idle thread */
 
 	int		needexec;
 	Execargs	exec;		/* exec argument */
@@ -185,6 +186,7 @@ void		_threadinitstack(Thread*, void(*)(void*), void*);
 void*	_threadmalloc(long, int);
 void		_threadnote(void*, char*);
 void		_threadready(Thread*);
+void		_threadidle(void);
 ulong	_threadrendezvous(ulong, ulong);
 void		_threadsignal(void);
 void		_threadsysfatal(char*, va_list);
@@ -192,6 +194,7 @@ long		_xdec(long*);
 void		_xinc(long*);
 void		_threadremove(Proc*, Thread*);
 
+extern int	_threadmultiproc;
 extern int			_threaddebuglevel;
 extern char*		_threadexitsallstatus;
 extern Pqueue		_threadpq;