pollout: handle request for pollout during pollout service

lib/pollfd.c

@@ -33,6 +33,26 @@ _lws_change_pollfd(struct lws *wsi, int _and, int _or, struct lws_pollargs *pa)
 	if (!wsi || wsi->position_in_fds_table < 0)
 		return 0;
 
+	if (wsi->handling_pollout && !_and && _or == LWS_POLLOUT) {
+		/*
+		 * Happening alongside service thread handling POLLOUT.
+		 * The danger is when he is finished, he will disable POLLOUT,
+		 * countermanding what we changed here.
+		 *
+		 * Instead of changing the fds, inform the service thread
+		 * what happened, and ask it to leave POLLOUT active on exit
+		 */
+		wsi->leave_pollout_active = 1;
+		/*
+		 * by definition service thread is not in poll wait, so no need
+		 * to cancel service
+		 */
+
+		lwsl_debug("%s: using leave_pollout_active\n", __func__);
+
+		return 0;
+	}
+
 	context = wsi->context;
 	pt = &context->pt[(int)wsi->tsi];
 	assert(wsi->position_in_fds_table >= 0 &&

lib/private-libwebsockets.h

@@ -1502,7 +1502,7 @@ struct lws {
 	unsigned int sending_chunked:1;
 	unsigned int already_did_cce:1;
 	unsigned int told_user_closed:1;
-	unsigned int :1;
+
 #if defined(LWS_WITH_ESP8266)
 	unsigned int pending_send_completion:3;
 	unsigned int close_is_pending_send_completion:1;
@@ -1532,6 +1532,10 @@ struct lws {
 	unsigned int redirect_to_https:1;
 #endif
 
+	/* volatile to make sure code is aware other thread can change */
+	volatile unsigned int handling_pollout:1;
+	volatile unsigned int leave_pollout_active:1;
+
 #ifndef LWS_NO_CLIENT
 	unsigned short c_port;
 #endif

lib/service.c

@@ -64,6 +64,14 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 
 	//lwsl_err("%s: %p\n", __func__, wsi);
 
+	wsi->leave_pollout_active = 0;
+	wsi->handling_pollout = 1;
+	/*
+	 * if another thread wants POLLOUT on us, from here on while
+	 * handling_pollout is set, he will only set leave_pollout_active.
+	 * If we are going to disable POLLOUT, we will check that first.
+	 */
+
 	/*
 	 * user callback is lowest priority to get these notifications
 	 * actually, since other pending things cannot be disordered
@@ -77,13 +85,13 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		if (lws_issue_raw(wsi, wsi->trunc_alloc + wsi->trunc_offset,
 				  wsi->trunc_len) < 0) {
 			lwsl_info("%s signalling to close\n", __func__);
-			return -1;
+			goto bail_die;
 		}
 		/* leave POLLOUT active either way */
-		return 0;
+		goto bail_ok;
 	} else
 		if (wsi->state == LWSS_FLUSHING_STORED_SEND_BEFORE_CLOSE)
-			return -1; /* retry closing now */
+			goto bail_die; /* retry closing now */
 
 	if (wsi->mode == LWSCM_WSCL_ISSUE_HTTP_BODY)
 		goto user_service;
@@ -105,7 +113,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		wsi->pps = LWS_PPS_NONE;
 		lws_rx_flow_control(wsi, 1);
 
-		return 0; /* leave POLLOUT active */
+		goto bail_ok; /* leave POLLOUT active */
 	}
 #endif
 
@@ -134,16 +142,16 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		n = lws_write(wsi, &wsi->u.ws.ping_payload_buf[LWS_PRE],
 			      wsi->u.ws.ping_payload_len, write_type);
 		if (n < 0)
-			return -1;
+			goto bail_die;
 
 		/* well he is sent, mark him done */
 		wsi->u.ws.ping_pending_flag = 0;
 		if (wsi->u.ws.payload_is_close)
 			/* oh... a close frame was it... then we are done */
-			return -1;
+			goto bail_die;
 
 		/* otherwise for PING, leave POLLOUT active either way */
-		return 0;
+		goto bail_ok;
 	}
 
 	if (wsi->state == LWSS_ESTABLISHED &&
@@ -155,7 +163,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		n = lws_write(wsi, &wsi->u.ws.ping_payload_buf[LWS_PRE],
 			      0, LWS_WRITE_PING);
 		if (n < 0)
-			return -1;
+			goto bail_die;
 
 		/*
 		 * we apparently were able to send the PING in a reasonable time
@@ -166,7 +174,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		lws_set_timeout(wsi, PENDING_TIMEOUT_WS_PONG_CHECK_GET_PONG,
 				wsi->context->timeout_secs);
 
-		return 0;
+		goto bail_ok;
 	}
 
 	/* Priority 4: if we are closing, not allowed to send more data frags
@@ -185,16 +193,16 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 	if (wsi->state == LWSS_ESTABLISHED && wsi->u.ws.tx_draining_ext) {
 		lwsl_ext("SERVICING TX EXT DRAINING\n");
 		if (lws_write(wsi, NULL, 0, LWS_WRITE_CONTINUATION) < 0)
-			return -1;
+			goto bail_die;
 		/* leave POLLOUT active */
-		return 0;
+		goto bail_ok;
 	}
 
 	/* Priority 6: user can get the callback
 	 */
 	m = lws_ext_cb_active(wsi, LWS_EXT_CB_IS_WRITEABLE, NULL, 0);
 	if (m)
-		return -1;
+		goto bail_die;
 #ifndef LWS_NO_EXTENSIONS
 	if (!wsi->extension_data_pending)
 		goto user_service;
@@ -225,7 +233,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 					       &eff_buf, 0);
 		if (m < 0) {
 			lwsl_err("ext reports fatal error\n");
-			return -1;
+			goto bail_die;
 		}
 		if (m)
 			/*
@@ -241,7 +249,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 					  eff_buf.token_len);
 			if (n < 0) {
 				lwsl_info("closing from POLLOUT spill\n");
-				return -1;
+				goto bail_die;
 			}
 			/*
 			 * Keep amount spilled small to minimize chance of this
@@ -249,7 +257,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 			if (n != eff_buf.token_len) {
 				lwsl_err("Unable to spill ext %d vs %d\n",
 							  eff_buf.token_len, n);
-				return -1;
+				goto bail_die;
 			}
 		} else
 			continue;
@@ -277,7 +285,7 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 		 * when we come back here and there's nothing more to spill.
 		 */
 
-		return 0;
+		goto bail_ok;
 	}
 #ifndef LWS_NO_EXTENSIONS
 	wsi->extension_data_pending = 0;
@@ -285,15 +293,31 @@ lws_handle_POLLOUT_event(struct lws *wsi, struct lws_pollfd *pollfd)
 user_service:
 	/* one shot */
 
-	if (pollfd)
+	if (pollfd) {
+		int eff = wsi->leave_pollout_active;
+
+		if (!eff)
 			if (lws_change_pollfd(wsi, LWS_POLLOUT, 0)) {
 				lwsl_info("failed at set pollfd\n");
-			return 1;
+				goto bail_die;
+			}
+
+		wsi->handling_pollout = 0;
+
+		/* cannot get leave_pollout_active set after the above */
+
+		if (!eff && wsi->leave_pollout_active)
+			/* got set inbetween sampling eff and clearing
+			 * handling_pollout, force POLLOUT on */
+			lws_calllback_as_writeable(wsi);
+
+		wsi->leave_pollout_active = 0;
 	}
 
 	if (wsi->mode != LWSCM_WSCL_ISSUE_HTTP_BODY &&
 	    !wsi->hdr_parsing_completed)
-		return 0;
+		goto bail_ok;
+
 
 #ifdef LWS_WITH_CGI
 user_service_go_again:
@@ -321,7 +345,7 @@ user_service_go_again:
 	wsi->u.http2.requested_POLLOUT = 0;
 	if (!wsi->u.http2.initialized) {
 		lwsl_info("pollout on uninitialized http2 conn\n");
-		return 0;
+		goto bail_ok;
 	}
 
 	lwsl_info("%s: doing children\n", __func__);
@@ -344,10 +368,30 @@ user_service_go_again:
 
 	lwsl_info("%s: completed\n", __func__);
 
-	return 0;
+	goto bail_ok;
 notify:
 #endif
+	wsi->handling_pollout = 0;
+	wsi->leave_pollout_active = 0;
+
 	return lws_calllback_as_writeable(wsi);
+
+	/*
+	 * since these don't disable the POLLOUT, they are always doing the
+	 * right thing for leave_pollout_active whether it was set or not.
+	 */
+
+bail_ok:
+	wsi->handling_pollout = 0;
+	wsi->leave_pollout_active = 0;
+
+	return 0;
+
+bail_die:
+	wsi->handling_pollout = 0;
+	wsi->leave_pollout_active = 0;
+
+	return -1;
 }
 
 int