diff --git a/sdk/BUILD.gn b/sdk/BUILD.gn
index e9a8dbf..95221ca 100644
--- a/sdk/BUILD.gn
+++ b/sdk/BUILD.gn
@@ -1044,6 +1044,7 @@
         "../rtc_base:network_constants",
         "../rtc_base:safe_conversions",
         "../rtc_base:stringutils",
+        "../rtc_base:threading",
         "../rtc_base:timeutils",
         "../stats:rtc_stats",
         "../system_wrappers:field_trial",
diff --git a/sdk/objc/api/peerconnection/RTCMediaStream.mm b/sdk/objc/api/peerconnection/RTCMediaStream.mm
index a6292b5..beb4a7a 100644
--- a/sdk/objc/api/peerconnection/RTCMediaStream.mm
+++ b/sdk/objc/api/peerconnection/RTCMediaStream.mm
@@ -10,8 +10,6 @@
 
 #import "RTCMediaStream+Private.h"
 
-#include <vector>
-
 #import "RTCAudioTrack+Private.h"
 #import "RTCMediaStreamTrack+Private.h"
 #import "RTCPeerConnectionFactory+Private.h"
@@ -20,8 +18,9 @@
 
 @implementation RTC_OBJC_TYPE (RTCMediaStream) {
   RTC_OBJC_TYPE(RTCPeerConnectionFactory) * _factory;
-  NSMutableArray *_audioTracks;
-  NSMutableArray *_videoTracks;
+  rtc::Thread *_signalingThread;
+  NSMutableArray *_audioTracks /* accessed on _signalingThread */;
+  NSMutableArray *_videoTracks /* accessed on _signalingThread */;
   rtc::scoped_refptr<webrtc::MediaStreamInterface> _nativeMediaStream;
 }
 
@@ -36,10 +35,18 @@
 }
 
 - (NSArray<RTC_OBJC_TYPE(RTCAudioTrack) *> *)audioTracks {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<NSArray<RTC_OBJC_TYPE(RTCAudioTrack) *> *>(
+        RTC_FROM_HERE, [self]() { return self.audioTracks; });
+  }
   return [_audioTracks copy];
 }
 
 - (NSArray<RTC_OBJC_TYPE(RTCVideoTrack) *> *)videoTracks {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<NSArray<RTC_OBJC_TYPE(RTCVideoTrack) *> *>(
+        RTC_FROM_HERE, [self]() { return self.videoTracks; });
+  }
   return [_videoTracks copy];
 }
 
@@ -48,33 +55,52 @@
 }
 
 - (void)addAudioTrack:(RTC_OBJC_TYPE(RTCAudioTrack) *)audioTrack {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<void>(
+        RTC_FROM_HERE, [audioTrack, self]() { return [self addAudioTrack:audioTrack]; });
+  }
   if (_nativeMediaStream->AddTrack(audioTrack.nativeAudioTrack)) {
     [_audioTracks addObject:audioTrack];
   }
 }
 
 - (void)addVideoTrack:(RTC_OBJC_TYPE(RTCVideoTrack) *)videoTrack {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<void>(
+        RTC_FROM_HERE, [videoTrack, self]() { return [self addVideoTrack:videoTrack]; });
+  }
   if (_nativeMediaStream->AddTrack(videoTrack.nativeVideoTrack)) {
     [_videoTracks addObject:videoTrack];
   }
 }
 
 - (void)removeAudioTrack:(RTC_OBJC_TYPE(RTCAudioTrack) *)audioTrack {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<void>(
+        RTC_FROM_HERE, [audioTrack, self]() { return [self removeAudioTrack:audioTrack]; });
+  }
   NSUInteger index = [_audioTracks indexOfObjectIdenticalTo:audioTrack];
-  NSAssert(index != NSNotFound,
-           @"|removeAudioTrack| called on unexpected RTC_OBJC_TYPE(RTCAudioTrack)");
-  if (index != NSNotFound &&
-      _nativeMediaStream->RemoveTrack(audioTrack.nativeAudioTrack)) {
+  if (index == NSNotFound) {
+    RTC_LOG(LS_INFO) << "|removeAudioTrack| called on unexpected RTC_OBJC_TYPE(RTCAudioTrack)";
+    return;
+  }
+  if (_nativeMediaStream->RemoveTrack(audioTrack.nativeAudioTrack)) {
     [_audioTracks removeObjectAtIndex:index];
   }
 }
 
 - (void)removeVideoTrack:(RTC_OBJC_TYPE(RTCVideoTrack) *)videoTrack {
+  if (!_signalingThread->IsCurrent()) {
+    return _signalingThread->Invoke<void>(
+        RTC_FROM_HERE, [videoTrack, self]() { return [self removeVideoTrack:videoTrack]; });
+  }
   NSUInteger index = [_videoTracks indexOfObjectIdenticalTo:videoTrack];
-  NSAssert(index != NSNotFound,
-           @"|removeVideoTrack| called on unexpected RTC_OBJC_TYPE(RTCVideoTrack)");
-  if (index != NSNotFound &&
-      _nativeMediaStream->RemoveTrack(videoTrack.nativeVideoTrack)) {
+  if (index == NSNotFound) {
+    RTC_LOG(LS_INFO) << "|removeVideoTrack| called on unexpected RTC_OBJC_TYPE(RTCVideoTrack)";
+    return;
+  }
+
+  if (_nativeMediaStream->RemoveTrack(videoTrack.nativeVideoTrack)) {
     [_videoTracks removeObjectAtIndex:index];
   }
 }
@@ -98,6 +124,7 @@
   NSParameterAssert(nativeMediaStream);
   if (self = [super init]) {
     _factory = factory;
+    _signalingThread = factory.signalingThread;
 
     webrtc::AudioTrackVector audioTracks = nativeMediaStream->GetAudioTracks();
     webrtc::VideoTrackVector videoTracks = nativeMediaStream->GetVideoTracks();
diff --git a/sdk/objc/api/peerconnection/RTCPeerConnectionFactory+Private.h b/sdk/objc/api/peerconnection/RTCPeerConnectionFactory+Private.h
index ef61c2e..9613646 100644
--- a/sdk/objc/api/peerconnection/RTCPeerConnectionFactory+Private.h
+++ b/sdk/objc/api/peerconnection/RTCPeerConnectionFactory+Private.h
@@ -12,6 +12,7 @@
 
 #include "api/peer_connection_interface.h"
 #include "api/scoped_refptr.h"
+#include "rtc_base/thread.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -26,6 +27,9 @@
     @property(nonatomic,
               readonly) rtc::scoped_refptr<webrtc::PeerConnectionFactoryInterface> nativeFactory;
 
+@property(nonatomic, readonly) rtc::Thread* signalingThread;
+@property(nonatomic, readonly) rtc::Thread* workerThread;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/sdk/objc/api/peerconnection/RTCPeerConnectionFactory.mm b/sdk/objc/api/peerconnection/RTCPeerConnectionFactory.mm
index 4e5aa19..99b9363 100644
--- a/sdk/objc/api/peerconnection/RTCPeerConnectionFactory.mm
+++ b/sdk/objc/api/peerconnection/RTCPeerConnectionFactory.mm
@@ -331,4 +331,12 @@
   _hasStartedAecDump = NO;
 }
 
+- (rtc::Thread *)signalingThread {
+  return _signalingThread.get();
+}
+
+- (rtc::Thread *)workerThread {
+  return _workerThread.get();
+}
+
 @end
diff --git a/sdk/objc/api/peerconnection/RTCVideoTrack.mm b/sdk/objc/api/peerconnection/RTCVideoTrack.mm
index 8944d26..fb015c6 100644
--- a/sdk/objc/api/peerconnection/RTCVideoTrack.mm
+++ b/sdk/objc/api/peerconnection/RTCVideoTrack.mm
@@ -17,7 +17,8 @@
 #import "helpers/NSString+StdString.h"
 
 @implementation RTC_OBJC_TYPE (RTCVideoTrack) {
-  NSMutableArray *_adapters;
+  rtc::Thread *_workerThread;
+  NSMutableArray *_adapters /* accessed on _workerThread */;
 }
 
 @synthesize source = _source;
@@ -46,6 +47,7 @@
   NSParameterAssert(type == RTCMediaStreamTrackTypeVideo);
   if (self = [super initWithFactory:factory nativeTrack:nativeMediaTrack type:type]) {
     _adapters = [NSMutableArray array];
+    _workerThread = factory.workerThread;
   }
   return self;
 }
@@ -69,10 +71,15 @@
 }
 
 - (void)addRenderer:(id<RTC_OBJC_TYPE(RTCVideoRenderer)>)renderer {
+  if (!_workerThread->IsCurrent()) {
+    _workerThread->Invoke<void>(RTC_FROM_HERE, [renderer, self] { [self addRenderer:renderer]; });
+    return;
+  }
+
   // Make sure we don't have this renderer yet.
   for (RTCVideoRendererAdapter *adapter in _adapters) {
     if (adapter.videoRenderer == renderer) {
-      NSAssert(NO, @"|renderer| is already attached to this track");
+      RTC_LOG(LS_INFO) << "|renderer| is already attached to this track";
       return;
     }
   }
@@ -85,6 +92,11 @@
 }
 
 - (void)removeRenderer:(id<RTC_OBJC_TYPE(RTCVideoRenderer)>)renderer {
+  if (!_workerThread->IsCurrent()) {
+    _workerThread->Invoke<void>(RTC_FROM_HERE,
+                                [renderer, self] { [self removeRenderer:renderer]; });
+    return;
+  }
   __block NSUInteger indexToRemove = NSNotFound;
   [_adapters enumerateObjectsUsingBlock:^(RTCVideoRendererAdapter *adapter,
                                           NSUInteger idx,
@@ -95,6 +107,7 @@
     }
   }];
   if (indexToRemove == NSNotFound) {
+    RTC_LOG(LS_INFO) << "removeRenderer called with a renderer that has not been previously added";
     return;
   }
   RTCVideoRendererAdapter *adapterToRemove =