ratrace: avoid blank line prints, make writer the parent

when there where multiple syscalls returning out of order,
it would print blank lines between the exits. avoid this
by remembering if the last char written was a newline and
conditionally insert newline on out of order return.

sometimes, ratrace would return before all messages have
been printed. make the writer process the parent so ratrace
wont exit until all readers are finished avoiding the
problem.

sys/src/cmd/ratrace.c

@@ -9,7 +9,7 @@ enum {
 Channel *out;
 Channel *quit;
 Channel *forkc;
-int nread = 0;
+int readers = 1;
 
 typedef struct Msg Msg;
 struct Msg {
@@ -36,8 +36,10 @@ die(Reader *r)
 	snprint(s->buf, sizeof(s->buf), " = %r\n");
 	s->pid = r->pid;
 	sendp(quit, s);
-	close(r->tfd);
+	if(r->tfd >= 0)
-	close(r->cfd);
+		close(r->tfd);
+	if(r->cfd >= 0)
+		close(r->cfd);
 	threadexits(nil);
 }
 
@@ -105,13 +107,12 @@ reader(void *v)
 }
 
 void
-writer(void *arg)
+writer(int lastpid)
 {
-	int lastpid;
+	char lastc = -1;
 	Alt a[4];
 	Msg *s;
-
+	int n;
-	lastpid = (int)(uintptr)arg;
 
 	a[0].op = CHANRCV;
 	a[0].c = quit;
@@ -124,20 +125,29 @@ writer(void *arg)
 	a[2].v = nil;
 	a[3].op = CHANEND;
 
-	while(nread > 0){
+	while(readers > 0){
 		switch(alt(a)){
 		case 0:
-			nread--;
+			readers--;
 		case 1:
 			if(s->pid != lastpid){
 				lastpid = s->pid;
-				fprint(2, s->buf[1]=='='? "\n%d ...": "\n", lastpid);
+				if(lastc != '\n'){
+					lastc = '\n';
+					write(2, &lastc, 1);
+				}
+				if(s->buf[1] == '=')
+					fprint(2, "%d ...", lastpid);
+			}
+			n = strlen(s->buf);
+			if(n > 0){
+				write(2, s->buf, n);
+				lastc = s->buf[n-1];
 			}
-			write(2, s->buf, strlen(s->buf));
 			free(s);
 			break;
 		case 2:
-			nread++;
+			readers++;
 			break;
 		}
 	}
@@ -196,7 +206,8 @@ threadmain(int argc, char **argv)
 	out   = chancreate(sizeof(Msg*), 0);
 	quit  = chancreate(sizeof(Msg*), 0);
 	forkc = chancreate(sizeof(void*), 0);
-	nread++;
+	procrfork(reader, (void*)pid, Stacksize, 0);
-	procrfork(writer, (void*)pid, Stacksize, 0);
+
-	reader((void*)pid);
+	writer(pid);
+	threadexits(nil);
 }