charles thoughts on alarm:
- do not leave 0 with a special meaning in the alarm list,
- do not leave stale pointers in the list

a nix version should be forthcoming

Reference: /n/atom/patch/applied/alarm-charles
Date: Wed Jan 29 03:56:15 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/swap.c	Wed Jan 29 03:54:48 2014
+++ /sys/src/9/port/swap.c	Wed Jan 29 03:54:49 2014
@@ -439,9 +439,3 @@
 
 	swapimage.c = c;
 }
-
-int
-swapfull(void)
-{
-	return swapalloc.free < conf.nswap/10;
-}
--- /sys/src/9/port/portfns.h	Wed Jan 29 03:54:50 2014
+++ /sys/src/9/port/portfns.h	Wed Jan 29 03:54:51 2014
@@ -303,9 +303,9 @@
 int		readnum(ulong, char*, ulong, ulong, int);
 int		readstr(ulong, char*, ulong, char*);
 void		ready(Proc*);
-void*		realloc(void *v, ulong size);
+void*		realloc(void*, usize);
 void		rebootcmd(int, char**);
-void		reboot(void*, void*, ulong);
+void		reboot(void*, void*, usize);
 void		relocateseg(Segment*, ulong);
 void		renameuser(char*, char*);
 void		resched(char*);
@@ -339,8 +339,8 @@
 void		splxpc(int);
 char*		srvname(Chan*);
 int		swapcount(ulong);
-int		swapfull(void);
 void		swapinit(void);
+#define		tickscmp(a, b)  ((long)((a)-(b)))
 void		timeradd(Timer*);
 void		timerdel(Timer*);
 void		timersinit(void);
--- /sys/src/9/port/alarm.c	Wed Jan 29 03:54:52 2014
+++ /sys/src/9/port/alarm.c	Wed Jan 29 03:54:53 2014
@@ -10,25 +10,25 @@
 void
 alarmkproc(void*)
 {
-	Proc *rp;
+	Proc *rp, **l;
 	ulong now;
 
 	for(;;){
 		now = MACHP(0)->ticks;
 		qlock(&alarms);
-		for(rp = alarms.head; rp != nil; rp = rp->palarm){
-			if(rp->alarm == 0)
-				continue;
-			if((long)(now - rp->alarm) < 0)
-				break;
-			if(canqlock(&rp->debug))
-				break;
-			if(rp->alarm != 0)
-				postnote(rp, 0, "alarm", NUser);
-			rp->alarm = 0;
-			qunlock(&rp->debug);
+		l = &alarms.head;
+		while((rp = *l) != nil && tickscmp(now, rp->alarm) >= 0){
+			if(canqlock(&rp->debug)){
+				if(!waserror()){
+					postnote(rp, 0, "alarm", NUser);
+					poperror();
+				}
+				qunlock(&rp->debug);
+				rp->alarm = 0;
+				*l = rp->palarm;
+			}else
+				l = &rp->palarm;
 		}
-		alarms.head = rp;
 		qunlock(&alarms);
 
 		sleep(&alarmr, return0, 0);
@@ -42,25 +42,39 @@
 checkalarms(void)
 {
 	Proc *p;
-	ulong now;
 
 	p = alarms.head;
-	now = MACHP(0)->ticks;
-
-	if(p != nil)
-	if(p->alarm == 0 || (long)(now - p->alarm) >= 0)
+	if(p != nil && tickscmp(MACHP(0)->ticks, p->alarm) >= 0)
 		wakeup(&alarmr);
 }
 
+static void
+disalarm(Proc *p)
+{
+	Proc **l, *f;
+
+	qlock(&alarms);
+	for(l = &alarms.head; (f = *l) != nil; l = &f->palarm){
+		if(f == p){
+			*l = f->palarm;
+			f->palarm = nil;
+			break;
+		}
+	}
+	qunlock(&alarms);
+}
+
 ulong
 procalarm(ulong time)
 {
 	Proc **l, *f;
 	ulong when, old;
 
-	if(up->alarm)
-		old = tk2ms(up->alarm - MACHP(0)->ticks);
-	else
+	old = up->alarm;
+	if(up->alarm){
+		disalarm(up);
+		old = tk2ms(old - MACHP(0)->ticks);
+	}else
 		old = 0;
 	if(time == 0) {
 		up->alarm = 0;
@@ -71,25 +85,12 @@
 		when = 1;
 
 	qlock(&alarms);
+	up->alarm = when;
 	l = &alarms.head;
-	for(f = *l; f; f = f->palarm) {
-		if(up == f){
-			*l = f->palarm;
-			break;
-		}
-		l = &f->palarm;
-	}
-	up->palarm = 0;
-	l = &alarms.head;
-	for(f = *l; f != nil; f = f->palarm) {
-		time = f->alarm;
-		if(time != 0 && (long)(time - when) >= 0)
-			break;
+	while((f = *l) != nil && tickscmp(f->alarm, when) < 0)
 		l = &f->palarm;
-	}
-	up->palarm = f;
+	up->palarm = *l;
 	*l = up;
-	up->alarm = when;
 	qunlock(&alarms);
 
 	return old;
--- /sys/src/9/port/proc.c	Wed Jan 29 03:54:56 2014
+++ /sys/src/9/port/proc.c	Wed Jan 29 03:54:57 2014
@@ -621,6 +621,7 @@
 		p->procctl = 0;
 	p->syscalltrace = 0;	
 	p->notepending = 0;
+	p->nnote = 0;
 	p->ureg = 0;
 	p->privatemem = 0;
 	p->noswap = 0;
@@ -1047,8 +1048,9 @@
 
 	if(up->syscalltrace)
 		free(up->syscalltrace);
-	up->alarm = 0;
-	if (up->tt)
+	if(up->alarm != 0)
+		procalarm(0);
+	if(up->tt)
 		timerdel(up);
 	pt = proctrace;
 	if(pt)
@@ -1346,7 +1348,11 @@
 	Proc *p;
 	static Pgrp *kpgrp;
 
+	while(waserror())
+		;
 	p = newproc();
+	poperror();
+
 	p->psstate = 0;
 	p->procmode = 0640;
 	p->kp = 1;