support for low and high watermarks

svn:r101

buffer.c

@@ -88,6 +88,7 @@ int
 evbuffer_add(struct evbuffer *buf, u_char *data, size_t datlen)
 {
 	size_t need = buf->off + datlen;
+	size_t oldoff = buf->off;
 
 	if (buf->totallen < need) {
 		void *newbuf;
@@ -108,19 +109,30 @@ evbuffer_add(struct evbuffer *buf, u_char *data, size_t datlen)
 	memcpy(buf->buffer + buf->off, data, datlen);
 	buf->off += datlen;
 
+	if (datlen && buf->cb != NULL)
+		(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);
+
 	return (0);
 }
 
 void
 evbuffer_drain(struct evbuffer *buf, size_t len)
 {
+	size_t oldoff = buf->off;
+
 	if (len >= buf->off) {
 		buf->off = 0;
-		return;
+		goto done;
 	}
 
 	memmove(buf->buffer, buf->buffer + len, buf->off - len);
 	buf->off -= len;
+
+ done:
+	/* Tell someone about changes in this buffer */
+	if (buf->off != oldoff && buf->cb != NULL)
+		(*buf->cb)(buf, oldoff, buf->off, buf->cbarg);
+
 }
 
 int
@@ -176,3 +188,11 @@ evbuffer_find(struct evbuffer *buffer, u_char *what, size_t len)
 
 	return (NULL);
 }
+
+void evbuffer_setcb(struct evbuffer *buffer,
+    void (*cb)(struct evbuffer *, size_t, size_t, void *),
+    void *cbarg)
+{
+	buffer->cb = cb;
+	buffer->cbarg = cbarg;
+}

evbuffer.c

@@ -41,12 +41,34 @@ bufferevent_add(struct event *ev, int timeout)
 	return (event_add(ev, ptv));
 }
 
+/* 
+ * This callback is executed when the size of the input buffer changes.
+ * We use it to apply back pressure on the reading side.
+ */
+
+void
+bufferevent_read_pressure_cb(struct evbuffer *buf, size_t old, size_t now,
+    void *arg) {
+	struct bufferevent *bufev = arg;
+	/* 
+	 * If we are below the watermak then reschedule reading if it's
+	 * still enabled.
+	 */
+	if (bufev->wm_read.high == 0 || now < bufev->wm_read.high) {
+		evbuffer_setcb(buf, NULL, NULL);
+
+		if (bufev->enabled & EV_READ)
+			bufferevent_add(&bufev->ev_read, bufev->timeout_read);
+	}
+}
+
 static void
 bufferevent_readcb(int fd, short event, void *arg)
 {
 	struct bufferevent *bufev = arg;
 	int res = 0;
 	short what = EVBUFFER_READ;
+	size_t len;
 
 	if (event == EV_TIMEOUT) {
 		what |= EVBUFFER_TIMEOUT;
@@ -69,6 +91,19 @@ bufferevent_readcb(int fd, short event, void *arg)
 
 	bufferevent_add(&bufev->ev_read, bufev->timeout_read);
 
+	/* See if this callbacks meets the water marks */
+	len = EVBUFFER_LENGTH(bufev->input);
+	if (bufev->wm_read.low != 0 && len < bufev->wm_read.low)
+		return;
+	if (bufev->wm_read.high != 0 && len > bufev->wm_read.high) {
+		struct evbuffer *buf = bufev->input;
+		event_del(&bufev->ev_read);
+
+		/* Now schedule a callback for us */
+		evbuffer_setcb(buf, bufferevent_read_pressure_cb, bufev);
+		return;
+	}
+
 	/* Invoke the user callback - must always be called last */
 	(*bufev->readcb)(bufev, bufev->cbarg);
 	return;
@@ -111,8 +146,11 @@ bufferevent_writecb(int fd, short event, void *arg)
 	if (EVBUFFER_LENGTH(bufev->output) != 0)
 		bufferevent_add(&bufev->ev_write, bufev->timeout_write);
 
-	/* Invoke the user callback if our buffer is drained */
-	if (EVBUFFER_LENGTH(bufev->output) == 0)
+	/*
+	 * Invoke the user callback if our buffer is drained or below the
+	 * low watermark.
+	 */
+	if (EVBUFFER_LENGTH(bufev->output) <= bufev->wm_write.low)
 		(*bufev->writecb)(bufev, bufev->cbarg);
 
 	return;
@@ -273,3 +311,26 @@ bufferevent_settimeout(struct bufferevent *bufev,
 	bufev->timeout_read = timeout_read;
 	bufev->timeout_write = timeout_write;
 }
+
+/*
+ * Sets the water marks
+ */
+
+void
+bufferevent_setwatermark(struct bufferevent *bufev, short events,
+    size_t lowmark, size_t highmark)
+{
+	if (events & EV_READ) {
+		bufev->wm_read.low = lowmark;
+		bufev->wm_read.high = highmark;
+	}
+
+	if (events & EV_WRITE) {
+		bufev->wm_write.low = lowmark;
+		bufev->wm_write.high = highmark;
+	}
+
+	/* If the watermarks changed then see if we should call read again */
+	bufferevent_read_pressure_cb(bufev->input,
+	    0, EVBUFFER_LENGTH(bufev->input), bufev);
+}

event.c

@@ -327,6 +327,10 @@ event_once(int fd, short events,
 	struct event_once *eonce;
 	struct timeval etv;
 
+	/* We cannot support signals that just fire once */
+	if (events & EV_SIGNAL)
+		return (-1);
+
 	if ((eonce = calloc(1, sizeof(struct event_once))) == NULL)
 		return (-1);
 
@@ -387,8 +391,10 @@ event_pending(struct event *ev, short event, struct timeval *tv)
 		flags |= ev->ev_res;
 	if (ev->ev_flags & EVLIST_TIMEOUT)
 		flags |= EV_TIMEOUT;
+	if (ev->ev_flags & EVLIST_SIGNAL)
+		flags |= EV_SIGNAL;
 
-	event &= (EV_TIMEOUT|EV_READ|EV_WRITE);
+	event &= (EV_TIMEOUT|EV_READ|EV_WRITE|EV_SIGNAL);
 
 	/* See if there is a timeout that we should report */
 	if (tv != NULL && (flags & event & EV_TIMEOUT))

event.h

@@ -173,6 +173,9 @@ struct evbuffer {
 
 	size_t totallen;
 	size_t off;
+
+	void (*cb)(struct evbuffer *, size_t, size_t, void *);
+	void *cbarg;
 };
 
 /* Just for error reporting - use other constants otherwise */
@@ -186,6 +189,11 @@ struct bufferevent;
 typedef void (*evbuffercb)(struct bufferevent *, void *);
 typedef void (*everrorcb)(struct bufferevent *, short what, void *);
 
+struct event_watermark {
+	size_t low;
+	size_t high;
+};
+
 struct bufferevent {
 	struct event ev_read;
 	struct event ev_write;
@@ -193,6 +201,9 @@ struct bufferevent {
 	struct evbuffer *input;
 	struct evbuffer *output;
 
+	struct event_watermark wm_read;
+	struct event_watermark wm_write;
+
 	evbuffercb readcb;
 	evbuffercb writecb;
 	everrorcb errorcb;
@@ -222,7 +233,6 @@ void bufferevent_settimeout(struct bufferevent *bufev,
 
 struct evbuffer *evbuffer_new(void);
 void evbuffer_free(struct evbuffer *);
-void evbuffer_free(struct evbuffer *);
 int evbuffer_add(struct evbuffer *, u_char *, size_t);
 int evbuffer_add_buffer(struct evbuffer *, struct evbuffer *);
 int evbuffer_add_printf(struct evbuffer *, char *fmt, ...);
@@ -230,6 +240,7 @@ void evbuffer_drain(struct evbuffer *, size_t);
 int evbuffer_write(struct evbuffer *, int);
 int evbuffer_read(struct evbuffer *, int, int);
 u_char *evbuffer_find(struct evbuffer *, u_char *, size_t);
+void evbuffer_setcb(struct evbuffer *, void (*)(struct evbuffer *, size_t, size_t, void *), void *);
 
 #ifdef __cplusplus
 }