rio: huge simplification of flush handling

xfidflush() now uses a simpler way to flush another xfid.

when we can send to Xfid.c channel, we know that the
xfid is completed. so all xfidflush() needs todo is to
do an alt sending to both Xfid.c and Xfid.flushc.

once the send to Xfid.c succeeds, we know the xfid is gone
and we can respond to the flush request.

theres no need to keep track of flush state anymore. so
Xfid.active and Xfid.flushing can be removed.

note, that it is ok to respond normally to a currently
flushed request.

3 files changed, 34 insertions, 125 deletions

diff --git a/sys/src/cmd/rio/dat.h b/sys/src/cmd/rio/dat.h
index dd7d560d5..454fcd9ac 100644
--- a/sys/src/cmd/rio/dat.h
+++ b/sys/src/cmd/rio/dat.h
@@ -258,8 +258,6 @@ struct Xfid
 		Fid		*f;
 		uchar	*buf;
 		Filsys	*fs;
-		QLock	active;
-		int		flushing;	/* another Xfid is trying to flush us */
 		int		flushtag;	/* our tag, so flush can find us */
 		Channel	*flushc;	/* channel(int) to notify us we're being flushed */
 };
diff --git a/sys/src/cmd/rio/fsys.c b/sys/src/cmd/rio/fsys.c
index 41db21b96..5e680ea85 100644
--- a/sys/src/cmd/rio/fsys.c
+++ b/sys/src/cmd/rio/fsys.c
@@ -270,8 +270,6 @@ filsysrespond(Filsys *fs, Xfid *x, Fcall *t, char *err)
 	free(x->buf);
 	x->buf = nil;
 	x->flushtag = -1;
-	if(x->flushing)
-		recv(x->flushc, nil);	/* wakeup flushing xfid */
 	return x;
 }
 
diff --git a/sys/src/cmd/rio/xfid.c b/sys/src/cmd/rio/xfid.c
index be7c65d9c..7cf7eadb6 100644
--- a/sys/src/cmd/rio/xfid.c
+++ b/sys/src/cmd/rio/xfid.c
@@ -70,8 +70,6 @@ xfidallocthread(void*)
 				fprint(2, "%p incref %ld\n", x, x->ref);
 				error("incref");
 			}
-			if(x->flushing)
-				error("flushing in allocate");
 			if(x->flushtag != -1)
 				error("flushtag in allocate");
 			incref(x);
@@ -82,8 +80,6 @@ xfidallocthread(void*)
 				fprint(2, "%p decref %ld\n", x, x->ref);
 				error("decref");
 			}
-			if(x->flushing)
-				error("flushing in free");
 			if(x->flushtag != -1)
 				error("flushtag in free");
 			x->free = xfidfree;
@@ -114,8 +110,10 @@ xfidctl(void *arg)
 	threadsetname(buf);
 	for(;;){
 		f = recvp(x->c);
-		x->flushtag = x->tag;
-		(*f)(x);
+		if(f){
+			x->flushtag = x->tag;
+			(*f)(x);
+		}
 		if(decref(x) == 0)
 			sendp(cxfidfree, x);
 	}
@@ -146,28 +144,30 @@ xfidflush(Xfid *x)
 	sendul(x->fs->csyncflush, 0);
 
 	if(xf){
-		qlock(&xf->active);
-		if(xf->buf){	/* not responded yet? */
-			xf->flushing = TRUE;
-			qunlock(&xf->active);
-			sendul(xf->flushc, 0);
-			xf->flushing = FALSE;
-		}else{
-			qunlock(&xf->active);
-		}
-		if(decref(xf) == 0)
-			sendp(cxfidfree, xf);
+		enum { Done, Flush, End };
+		Alt alts[End+1];
+		void *f;
+		int z;
+
+		z = 0;
+		f = nil;
+
+		alts[Done].c = xf->c;
+		alts[Done].v = &f;
+		alts[Done].op = CHANSND;
+		alts[Flush].c = xf->flushc;
+		alts[Flush].v = &z;
+		alts[Flush].op = CHANSND;
+		alts[End].op = CHANEND;
+
+		while(alt(alts) != Done)
+			;
 	}
-
-	qlock(&x->active);
-	if(x->flushing){
-		qunlock(&x->active);
-		recv(x->flushc, nil);	/* wakeup flushing xfid */
+	if(nbrecv(x->flushc, nil)){
 		filsyscancel(x);
 		return;
 	}
 	filsysrespond(x->fs, x, &t, nil);
-	qunlock(&x->active);
 }
 
 void
@@ -439,16 +439,9 @@ xfidwrite(Xfid *x)
 		case CWdata:
 			break;
 		case CWgone:
-			qlock(&x->active);
-			if(!x->flushing){
-				filsysrespond(x->fs, x, &fc, Edeleted);
-				qunlock(&x->active);
-				free(r);
-				return;
-			}
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			/* no break */
+			filsysrespond(x->fs, x, &fc, Edeleted);
+			free(r);
+			return;
 		case CWflush:
 			free(r);
 			filsyscancel(x);
@@ -456,23 +449,11 @@ xfidwrite(Xfid *x)
 		}
 
 		/* received data */
-		qlock(&x->active);
-		if(x->flushing){
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			free(r);
-			pair.s = runemalloc(1);
-			pair.ns = 0;
-			send(cwm.cw, &pair);		/* wake up window with empty data */
-			filsyscancel(x);
-			return;
-		}
 		pair.s = r;
 		pair.ns = nr;
 		send(cwm.cw, &pair);
 		fc.count = x->count;
 		filsysrespond(x->fs, x, &fc, nil);
-		qunlock(&x->active);
 		return;
 
 	case Qconsctl:
@@ -678,15 +659,8 @@ xfidread(Xfid *x)
 		case CRdata:
 			break;
 		case CRgone:
-			qlock(&x->active);
-			if(!x->flushing){
-				filsysrespond(x->fs, x, &fc, Edeleted);
-				qunlock(&x->active);
-				return;
-			}
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			/* no break */
+			filsysrespond(x->fs, x, &fc, Edeleted);
+			return;
 		case CRflush:
 			filsyscancel(x);
 			return;
@@ -699,20 +673,10 @@ xfidread(Xfid *x)
 		pair.s = t;
 		pair.ns = cnt;
 		send(c1, &pair);
-		qlock(&x->active);
-		if(x->flushing){
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			recv(c2, nil);			/* wake up window and toss data */
-			free(t);
-			filsyscancel(x);
-			return;
-		}
 		recv(c2, &pair);
 		fc.data = pair.s;
 		fc.count = pair.ns;
 		filsysrespond(x->fs, x, &fc, nil);
-		qunlock(&x->active);
 		free(t);
 		break;
 
@@ -743,26 +707,9 @@ xfidread(Xfid *x)
 		case MRdata:
 			break;
 		case MRgone:
-			qlock(&x->active);
-			if(!x->flushing){
-				filsysrespond(x->fs, x, &fc, Edeleted);
-				qunlock(&x->active);
-				return;
-			}
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			/* no break */
-		case MRflush:
-			filsyscancel(x);
+			filsysrespond(x->fs, x, &fc, Edeleted);
 			return;
-		}
-
-		/* received data */
-		qlock(&x->active);
-		if(x->flushing){
-			qunlock(&x->active);
-			recv(x->flushc, nil);		/* wake up flushing xfid */
-			recv(mrm.cm, nil);			/* wake up window and toss data */
+		case MRflush:
 			filsyscancel(x);
 			return;
 		}
@@ -775,7 +722,6 @@ xfidread(Xfid *x)
 		fc.data = buf;
 		fc.count = min(n, cnt);
 		filsysrespond(x->fs, x, &fc, nil);
-		qunlock(&x->active);
 		break;
 
 	case Qkbd:
@@ -794,15 +740,8 @@ xfidread(Xfid *x)
 		case MRdata:
 			break;
 		case MRgone:
-			qlock(&x->active);
-			if(!x->flushing){
-				filsysrespond(x->fs, x, &fc, Edeleted);
-				qunlock(&x->active);
-				return;
-			}
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			/* no break */
+			filsysrespond(x->fs, x, &fc, Edeleted);
+			return;
 		case MRflush:
 			filsyscancel(x);
 			return;
@@ -810,18 +749,9 @@ xfidread(Xfid *x)
 
 		/* received data */
 		t = recvp(krm.ck);
-		qlock(&x->active);
-		if(x->flushing){
-			qunlock(&x->active);
-			free(t);		/* toss data */
-			recv(x->flushc, nil);		/* wake up flushing xfid */
-			filsyscancel(x);
-			return;
-		}
 		fc.data = t;
 		fc.count = strlen(t)+1;
 		filsysrespond(x->fs, x, &fc, nil);
-		qunlock(&x->active);
 		free(t);
 		break;
 
@@ -934,15 +864,8 @@ xfidread(Xfid *x)
 		case WCRdata:
 			break;
 		case WCRgone:
-			qlock(&x->active);
-			if(!x->flushing){
-				filsysrespond(x->fs, x, &fc, Edeleted);
-				qunlock(&x->active);
-				return;
-			}
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			/* no break */
+			filsysrespond(x->fs, x, &fc, Edeleted);
+			return;
 		case WCRflush:
 			filsyscancel(x);
 			return;
@@ -955,22 +878,12 @@ xfidread(Xfid *x)
 		pair.s = t;
 		pair.ns = cnt+1;
 		send(c1, &pair);
-		qlock(&x->active);
-		if(x->flushing){
-			qunlock(&x->active);
-			recv(x->flushc, nil);	/* wake up flushing xfid */
-			recv(c2, nil);			/* wake up window and toss data */
-			free(t);
-			filsyscancel(x);
-			return;
-		}
 		recv(c2, &pair);
 		fc.data = pair.s;
 		if(pair.ns > cnt)
 			pair.ns = cnt;
 		fc.count = pair.ns;
 		filsysrespond(x->fs, x, &fc, nil);
-		qunlock(&x->active);
 		free(t);
 		break;