for alsa, POLL{IN,OUT} events mean that a block can be read or

written (not a byte as unix files expect). Use "tickets" counters that
are reset to hdl->par.round on each POLL{IN,OUT} event. Limit read()
and write() to one block to ensure poll is always called at block
boundaries.

libsndio/sio_alsa.c

@@ -54,6 +54,7 @@ struct sio_alsa_hdl {
 	int running;
 	int events;
 	int ipartial, opartial;
+	int canread, canwrite;
 	char *itmpbuf, *otmpbuf;
 };
 
@@ -379,6 +380,8 @@ sio_alsa_start(struct sio_hdl *sh)
 	hdl->infds = 0;
 	hdl->onfds = 0;
 	hdl->running = 0;
+	hdl->canread = 0;
+	hdl->canwrite = 0;
 
 	if (hdl->sio.mode & SIO_PLAY) {
 		err = snd_pcm_prepare(hdl->opcm);
@@ -932,7 +935,12 @@ sio_alsa_read(struct sio_hdl *sh, void *buf, size_t len)
 			len = hdl->ibpf;
 		}
 	}
-	while ((n = snd_pcm_readi(hdl->ipcm, buf, len / hdl->ibpf)) < 0) {
+	todo = len / hdl->ibpf;
+	if (todo > hdl->canread)
+		todo = hdl->canread;
+	if (todo == 0)
+		return 0;
+	while ((n = snd_pcm_readi(hdl->ipcm, buf, todo)) < 0) {
 		if (n == -EINTR)
 			continue;
 		if (n == -EPIPE || n == -ESTRPIPE) {
@@ -950,6 +958,7 @@ sio_alsa_read(struct sio_hdl *sh, void *buf, size_t len)
 		hdl->sio.eof = 1;
 		return 0;
 	}
+	hdl->canread -= n;
 	hdl->idelta += n;
 	if (buf == hdl->itmpbuf) {
 		hdl->ipartial = hdl->ibpf;
@@ -977,7 +986,12 @@ sio_alsa_write(struct sio_hdl *sh, const void *buf, size_t len)
 		len = hdl->obpf;
 		buf = hdl->otmpbuf;
 	}
-	while ((n = snd_pcm_writei(hdl->opcm, buf, len / hdl->obpf)) < 0) {
+	todo = len / hdl->obpf;
+	if (todo > hdl->canwrite)
+		todo = hdl->canwrite;
+	if (todo == 0)
+		return 0;
+	while ((n = snd_pcm_writei(hdl->opcm, buf, todo)) < 0) {
 		if (n == -EINTR)
 			continue;
 		if (n == -ESTRPIPE || n == -EPIPE) {
@@ -990,6 +1004,7 @@ sio_alsa_write(struct sio_hdl *sh, const void *buf, size_t len)
 		}
 		return 0;
 	}
+	hdl->canwrite -= n;
 	hdl->odelta += n;
 	if (buf == hdl->otmpbuf) {
 		if (n > 0)
@@ -1054,32 +1069,37 @@ sio_alsa_pollfd(struct sio_hdl *sh, struct pollfd *pfd, int events)
 	if (!hdl->sio.started)
 		hdl->events = 0;
 	memset(pfd, 0, sizeof(struct pollfd) * hdl->nfds);
+	hdl->onfds = hdl->infds = 0;
 	if (hdl->events & POLLOUT) {
 		if (!hdl->running &&
 		    snd_pcm_state(hdl->opcm) == SND_PCM_STATE_RUNNING)
 			sio_alsa_onmove(hdl);
-		hdl->onfds = snd_pcm_poll_descriptors(hdl->opcm,
-		    pfd, hdl->nfds);
-		if (hdl->onfds < 0) {
-			DALSA("couldn't poll play descriptors", hdl->onfds);
-			hdl->sio.eof = 1;
-			return 0;
+		if (hdl->canwrite == 0) {
+			hdl->onfds = snd_pcm_poll_descriptors(hdl->opcm,
+			    pfd, hdl->nfds);
+			if (hdl->onfds < 0) {
+				DALSA("couldn't poll play descriptors",
+				    hdl->onfds);
+				hdl->sio.eof = 1;
+				return 0;
+			}
 		}
-	} else
-		hdl->onfds = 0;
+	}
 	if (hdl->events & POLLIN) {
 		if (!hdl->running &&
 		    snd_pcm_state(hdl->ipcm) == SND_PCM_STATE_RUNNING)
 			sio_alsa_onmove(hdl);
-		hdl->infds = snd_pcm_poll_descriptors(hdl->ipcm,
-		    pfd + hdl->onfds, hdl->nfds - hdl->onfds);
-		if (hdl->infds < 0) {
-			DALSA("couldn't poll rec descriptors", hdl->infds);
-			hdl->sio.eof = 1;
-			return 0;
+		if (hdl->canread == 0) {
+			hdl->infds = snd_pcm_poll_descriptors(hdl->ipcm,
+			    pfd + hdl->onfds, hdl->nfds - hdl->onfds);
+			if (hdl->infds < 0) {
+				DALSA("couldn't poll rec descriptors",
+				    hdl->infds);
+				hdl->sio.eof = 1;
+				return 0;
+			}
 		}
-	} else
-		hdl->infds = 0;
+	}
 	DPRINTFN(4, "sio_alsa_pollfd: events = %x, nfds = %d + %d\n",
 	    events, hdl->onfds, hdl->infds);
 
@@ -1097,7 +1117,7 @@ sio_alsa_revents(struct sio_hdl *sh, struct pollfd *pfd)
 	snd_pcm_sframes_t iused, oavail, oused;
 	snd_pcm_state_t istate, ostate;
 	unsigned short revents, r;
-	int nfds, err, i;
+	int nfds, err, i, cycle;
 
 	if (hdl->sio.eof)
 		return POLLHUP;
@@ -1106,27 +1126,41 @@ sio_alsa_revents(struct sio_hdl *sh, struct pollfd *pfd)
 		DPRINTFN(4, "sio_alsa_revents: pfds[%d].revents = %x\n",
 		    i, pfd[i].revents);
 	}
-	revents = nfds = 0;
+	cycle = revents = nfds = 0;
 	if (hdl->events & POLLOUT) {
-		err = snd_pcm_poll_descriptors_revents(hdl->opcm,
-		    pfd, hdl->onfds, &r);
-		if (err < 0) {
-			DALSA("couldn't get play events", err);
-			hdl->sio.eof = 1;
-			return POLLHUP;
-		}
+		if (hdl->canwrite == 0) {
+			err = snd_pcm_poll_descriptors_revents(hdl->opcm,
+			    pfd, hdl->onfds, &r);
+			if (err < 0) {
+				DALSA("couldn't get play events", err);
+				hdl->sio.eof = 1;
+				return POLLHUP;
+			}
+			if (r & POLLOUT) {
+				hdl->canwrite = hdl->par.round;
+				cycle = 1;
+			}
+		} else
+			r = POLLOUT;
 		revents |= r;
 		nfds += hdl->onfds;
 			
 	}
 	if (hdl->events & POLLIN) {
-		err = snd_pcm_poll_descriptors_revents(hdl->ipcm,
-		    pfd + nfds, hdl->infds, &r);
-		if (err < 0) {
-			DALSA("couldn't get rec events", err);
-			hdl->sio.eof = 1;
-			return POLLHUP;
-		}
+		if (hdl->canread == 0) {
+			err = snd_pcm_poll_descriptors_revents(hdl->ipcm,
+			    pfd + nfds, hdl->infds, &r);
+			if (err < 0) {
+				DALSA("couldn't get rec events", err);
+				hdl->sio.eof = 1;
+				return POLLHUP;
+			}
+			if (r & POLLIN) {
+				hdl->canread = hdl->par.round;
+				cycle = 1;
+			}
+		} else
+			r = POLLIN;
 		revents |= r;
 		nfds += hdl->infds;
 	}
@@ -1179,7 +1213,7 @@ sio_alsa_revents(struct sio_hdl *sh, struct pollfd *pfd)
 			hdl->iused = iused;
 		}
 	}
-	if (revents & (POLLIN | POLLOUT))
+	if (cycle && hdl->running)
 		sio_alsa_onmove(hdl);
 	return revents;
 }