fix(JingleSession) start modification queue after session is established.

Pull initial offer/answer tasks out of the modification queue and execute them right away. Only track and codec related operations that necessitate a renegotiation cycle need to be pushed to the modification queue. The queue execution is paused until the session is established. This avoids track operations being executed before the session is established. This fixes an issue seen in p2p connections where sources of the initiator are not signaled to the remote since the tracks are added while the initiator is waiting for a session-accept from the peer.

modules/util/AsyncQueue.js

         }
     }
 
+    /**
+     * Pauses the execution of the tasks on the queue.
+     */
+    pause() {
+        this._queue.pause();
+    }
+
     /**
      * The 'task' function will be given a callback it MUST call with either:
      *  1) No arguments if it was successful or
         this._queue.push(task, callback);
     }
 
+    /**
+     * Resumes the execution of the tasks on the queue.
+     */
+    resume() {
+        this._queue.resume();
+    }
+
     /**
      * Shutdowns the queue. All already queued tasks will execute, but no future tasks can be added. If a task is added
      * after the queue has been shutdown then the callback will be called with an error.

modules/xmpp/JingleSessionPC.js

         this.remoteSourceMaxFrameHeights = undefined;
 
         /**
-         * The queue used to serialize operations done on the peerconnection.
+         * The queue used to serialize operations done on the peerconnection after the session is established.
+         * The queue is paused until the first offer/answer cycle is complete. Only track or codec related
+         * operations which necessitate a renegotiation cycle need to be pushed to the modification queue.
+         * These tasks will be executed after the session has been established.
          *
          * @type {AsyncQueue}
          */
         this.modificationQueue = new AsyncQueue();
+        this.modificationQueue.pause();
 
         /**
          * Flag used to guarantee that the connection established event is
                 // then we should either call 'success' here immediately or
                 // modify sendSessionAccept method to do that
                 this.sendSessionAccept(() => {
+                    // Start processing tasks on the modification queue.
+                    logger.debug('Resuming the modification queue after session is established!');
+                    this.modificationQueue.resume();
+
                     success();
                     this.room.eventEmitter.emit(XMPPEvents.SESSION_ACCEPT, this);
 
         if (!this.isInitiator) {
             throw new Error('Trying to invite from the responder session');
         }
-        const workFunction = finishedCallback => {
-            const addTracks = [];
+        logger.debug(`${this} Executing invite task`);
 
-            for (const track of localTracks) {
-                addTracks.push(this.peerconnection.addTrack(track, this.isInitiator));
-            }
+        const addTracks = [];
 
-            Promise.all(addTracks)
-                .then(() => this.peerconnection.createOffer(this.mediaConstraints))
-                .then(offerSdp => this.peerconnection.setLocalDescription(offerSdp))
-                .then(() => {
-                    this.peerconnection.processLocalSdpForTransceiverInfo(localTracks);
+        for (const track of localTracks) {
+            addTracks.push(this.peerconnection.addTrack(track, this.isInitiator));
+        }
 
-                    // NOTE that the offer is obtained from the localDescription getter as it needs to go though
-                    // the transformation chain.
-                    this.sendSessionInitiate(this.peerconnection.localDescription.sdp);
-                })
-                .then(() => finishedCallback(), error => finishedCallback(error));
-        };
+        Promise.all(addTracks)
+            .then(() => this.peerconnection.createOffer(this.mediaConstraints))
+            .then(offerSdp => this.peerconnection.setLocalDescription(offerSdp))
+            .then(() => {
+                this.peerconnection.processLocalSdpForTransceiverInfo(localTracks);
 
-        logger.debug(`${this} Queued invite task`);
-        this.modificationQueue.push(
-            workFunction,
-            error => {
-                if (error) {
-                    logger.error(`${this} invite error`, error);
-                } else {
-                    logger.debug(`${this} invite executed - OK`);
-                }
+                // NOTE that the offer is obtained from the localDescription getter as it needs to go though
+                // the transformation chain.
+                this.sendSessionInitiate(this.peerconnection.localDescription.sdp);
+            })
+            .then(() => {
+                logger.debug(`${this} invite executed - OK`);
+            })
+            .catch(error => {
+                logger.error(`${this} invite error`, error);
             });
     }
 
         if (!this.isInitiator) {
             throw new Error('Trying to set an answer on the responder session');
         }
+        logger.debug(`${this} Executing setAnswer task`);
 
-        const workFunction = finishedCallback => {
-            const newRemoteSdp = this._processNewJingleOfferIq(jingleAnswer);
-            const oldLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
-            const remoteDescription = new RTCSessionDescription({
-                type: 'answer',
-                sdp: newRemoteSdp.raw
-            });
+        const newRemoteSdp = this._processNewJingleOfferIq(jingleAnswer);
+        const oldLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
+        const remoteDescription = new RTCSessionDescription({
+            type: 'answer',
+            sdp: newRemoteSdp.raw
+        });
 
-            this.peerconnection.setRemoteDescription(remoteDescription)
-                .then(() => {
-                    if (this.state === JingleSessionState.PENDING) {
-                        this.state = JingleSessionState.ACTIVE;
-                        const newLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
+        this.peerconnection.setRemoteDescription(remoteDescription)
+            .then(() => {
+                if (this.state === JingleSessionState.PENDING) {
+                    this.state = JingleSessionState.ACTIVE;
 
-                        this.sendContentModify();
-                        this.notifyMySSRCUpdate(oldLocalSdp, newLocalSdp);
-                    }
-                })
-                .then(() => finishedCallback(), error => finishedCallback(error));
-        };
+                    // Start processing tasks on the modification queue.
+                    logger.debug('Resuming the modification queue after session is established!');
+                    this.modificationQueue.resume();
+                    const newLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
 
-        logger.debug(`${this} Queued setAnswer task`);
-        this.modificationQueue.push(
-            workFunction,
-            error => {
-                if (error) {
-                    logger.error(`${this} setAnswer task failed: ${error}`);
-                } else {
-                    logger.debug(`${this} setAnswer task done`);
+                    this.sendContentModify();
+                    this.notifyMySSRCUpdate(oldLocalSdp, newLocalSdp);
                 }
+            })
+            .then(() => {
+                logger.debug(`${this} setAnswer task done`);
+            })
+            .catch(error => {
+                logger.error(`${this} setAnswer task failed: ${error}`);
             });
     }
 
      * offer/answer).
      */
     setOfferAnswerCycle(jingleOfferAnswerIq, success, failure, localTracks = []) {
-        const workFunction = finishedCallback => {
-            const addTracks = [];
-            const audioTracks = localTracks.filter(track => track.getType() === MediaType.AUDIO);
-            const videoTracks = localTracks.filter(track => track.getType() === MediaType.VIDEO);
-            let tracks = localTracks;
-
-            // Add only 1 video track at a time. Adding 2 or more video tracks to the peerconnection at the same time
-            // makes the browser go into a renegotiation loop by firing 'negotiationneeded' event after every
-            // renegotiation.
-            if (FeatureFlags.isMultiStreamSendSupportEnabled() && videoTracks.length > 1) {
-                tracks = [ ...audioTracks, videoTracks[0] ];
-            }
-            for (const track of tracks) {
-                addTracks.push(this.peerconnection.addTrack(track, this.isInitiator));
-            }
-            const newRemoteSdp = this._processNewJingleOfferIq(jingleOfferAnswerIq);
-            const oldLocalSdp = this.peerconnection.localDescription.sdp;
+        logger.debug(`${this} Executing setOfferAnswerCycle task`);
+
+        const addTracks = [];
+        const audioTracks = localTracks.filter(track => track.getType() === MediaType.AUDIO);
+        const videoTracks = localTracks.filter(track => track.getType() === MediaType.VIDEO);
+        let tracks = localTracks;
+
+        // Add only 1 video track at a time. Adding 2 or more video tracks to the peerconnection at the same time
+        // makes the browser go into a renegotiation loop by firing 'negotiationneeded' event after every
+        // renegotiation.
+        if (FeatureFlags.isMultiStreamSendSupportEnabled() && videoTracks.length > 1) {
+            tracks = [ ...audioTracks, videoTracks[0] ];
+        }
+        for (const track of tracks) {
+            addTracks.push(this.peerconnection.addTrack(track, this.isInitiator));
+        }
+        const newRemoteSdp = this._processNewJingleOfferIq(jingleOfferAnswerIq);
+        const oldLocalSdp = this.peerconnection.localDescription.sdp;
 
-            const bridgeSession = $(jingleOfferAnswerIq)
-                .find('>bridge-session[xmlns="http://jitsi.org/protocol/focus"]');
-            const bridgeSessionId = bridgeSession.attr('id');
+        const bridgeSession = $(jingleOfferAnswerIq).find('>bridge-session[xmlns="http://jitsi.org/protocol/focus"]');
+        const bridgeSessionId = bridgeSession.attr('id');
 
-            if (bridgeSessionId !== this._bridgeSessionId) {
-                this._bridgeSessionId = bridgeSessionId;
-            }
-            const remoteDescription = new RTCSessionDescription({
-                type: 'offer',
-                sdp: newRemoteSdp.raw
-            });
+        if (bridgeSessionId !== this._bridgeSessionId) {
+            this._bridgeSessionId = bridgeSessionId;
+        }
+        const remoteDescription = new RTCSessionDescription({
+            type: 'offer',
+            sdp: newRemoteSdp.raw
+        });
 
-            Promise.all(addTracks)
-                .then(() => this._responderRenegotiate(remoteDescription))
-                .then(() => {
-                    this.peerconnection.processLocalSdpForTransceiverInfo(tracks);
-                    if (this.state === JingleSessionState.PENDING) {
-                        this.state = JingleSessionState.ACTIVE;
-
-                        // #1 Sync up video transfer active/inactive only after the initial O/A cycle. We want to
-                        // adjust the video media direction only in the local SDP and the Jingle contents direction
-                        // included in the initial offer/answer is mapped to the remote SDP. Jingle 'content-modify'
-                        // IQ is processed in a way that it will only modify local SDP when remote peer is no longer
-                        // interested in receiving video content. Changing media direction in the remote SDP will mess
-                        // up our SDP translation chain (simulcast, video mute, RTX etc.)
-                        // #2 Sends the max frame height if it was set, before the session-initiate/accept
-                        if (this.isP2P
-                            && (!this._localVideoActive || this._sourceReceiverConstraints)) {
-                            this.sendContentModify();
-                        }
+        Promise.all(addTracks)
+            .then(() => this._responderRenegotiate(remoteDescription))
+            .then(() => {
+                this.peerconnection.processLocalSdpForTransceiverInfo(tracks);
+                if (this.state === JingleSessionState.PENDING) {
+                    this.state = JingleSessionState.ACTIVE;
+
+                    // #1 Sync up video transfer active/inactive only after the initial O/A cycle. We want to
+                    // adjust the video media direction only in the local SDP and the Jingle contents direction
+                    // included in the initial offer/answer is mapped to the remote SDP. Jingle 'content-modify'
+                    // IQ is processed in a way that it will only modify local SDP when remote peer is no longer
+                    // interested in receiving video content. Changing media direction in the remote SDP will mess
+                    // up our SDP translation chain (simulcast, video mute, RTX etc.)
+                    // #2 Sends the max frame height if it was set, before the session-initiate/accept
+                    if (this.isP2P
+                        && (!this._localVideoActive || this._sourceReceiverConstraints)) {
+                        this.sendContentModify();
                     }
+                }
 
-                    // Old local SDP will be available when we're setting answer for the first time, but not when offer
-                    // and it's fine since we're generating an answer now it will contain all our SSRCs.
-                    if (oldLocalSdp) {
-                        const newLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
+                // Old local SDP will be available when we're setting answer for the first time, but not when offer
+                // and it's fine since we're generating an answer now it will contain all our SSRCs.
+                if (oldLocalSdp) {
+                    const newLocalSdp = new SDP(this.peerconnection.localDescription.sdp);
 
-                        this.notifyMySSRCUpdate(new SDP(oldLocalSdp), newLocalSdp);
-                    }
-                })
-                .then(() => finishedCallback(), error => finishedCallback(error));
-        };
-
-        logger.debug(`${this} Queued setOfferAnswerCycle task`);
-        this.modificationQueue.push(
-            workFunction,
-            error => {
-                if (error) {
-                    logger.error(`${this} setOfferAnswerCycle task failed: ${error}`);
-                    failure(error);
-                } else {
-                    logger.debug(`${this} setOfferAnswerCycle task done`);
-                    success();
+                    this.notifyMySSRCUpdate(new SDP(oldLocalSdp), newLocalSdp);
                 }
+            })
+            .then(() => {
+                logger.debug(`${this} setOfferAnswerCycle task done`);
+                success();
+            })
+            .catch(error => {
+                logger.error(`${this} setOfferAnswerCycle task failed: ${error}`);
+                failure(error);
             });
     }
 
         newFingerprint.attr('hash', 'sha-1');
         newFingerprint.text('00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00');
 
-        // First set an offer with a rejected 'data' section
-        this.setOfferAnswerCycle(
-            jingleOfferElem,
-            () => {
-                // Now set the original offer(with the 'data' section)
-                this.setOfferAnswerCycle(
-                    originalOffer,
-                    () => {
-                        const localSDP = new SDP(this.peerconnection.localDescription.sdp);
+        const workFunction = finishedCallback => {
+            // First set an offer with a rejected 'data' section
+            this.setOfferAnswerCycle(
+                jingleOfferElem,
+                () => {
+                    // Now set the original offer(with the 'data' section)
+                    this.setOfferAnswerCycle(
+                        originalOffer,
+                        () => {
+                            const localSDP = new SDP(this.peerconnection.localDescription.sdp);
+
+                            if (typeof this.options.channelLastN === 'number' && this.options.channelLastN >= 0) {
+                                localSDP.initialLastN = this.options.channelLastN;
+                            }
 
-                        if (typeof this.options.channelLastN === 'number' && this.options.channelLastN >= 0) {
-                            localSDP.initialLastN = this.options.channelLastN;
-                        }
+                            this.sendTransportAccept(localSDP, success, failure);
 
-                        this.sendTransportAccept(localSDP, success, failure);
+                            this.room.eventEmitter.emit(
+                                XMPPEvents.ICE_RESTART_SUCCESS,
+                                this,
+                                originalOffer);
 
-                        this.room.eventEmitter.emit(
-                            XMPPEvents.ICE_RESTART_SUCCESS,
-                            this,
-                            originalOffer);
-                    },
-                    failure);
-            },
-            failure
-        );
+                            finishedCallback();
+                        }, error => finishedCallback(error)
+                    );
+                }, error => finishedCallback(error)
+            );
+        };
+
+        logger.debug(`${this} Queued ICE restart task`);
+
+        // Queue and execute
+        this.modificationQueue.push(
+            workFunction,
+            error => {
+                if (error) {
+                    logger.error(`${this} ICE restart task failed: ${error}`);
+                    failure(error);
+                } else {
+                    logger.debug(`${this} ICE restart task done`);
+                    success();
+                }
+            });
     }
 
     /**