address comments 2

src/objective-c/GRPCClient/GRPCCall.m

@@ -56,7 +56,6 @@ const char *kCFStreamVarName = "grpc_cfstream";
 // Make them read-write.
 @property(atomic, strong) NSDictionary *responseHeaders;
 @property(atomic, strong) NSDictionary *responseTrailers;
-@property(atomic) BOOL isWaitingForToken;
 
 - (instancetype)initWithHost:(NSString *)host
                         path:(NSString *)path

src/objective-c/RxLibrary/GRXForwardingWriter.m

@@ -72,7 +72,11 @@
 #pragma mark GRXWriter implementation
 
 - (GRXWriterState)state {
-  return _writer ? _writer.state : GRXWriterStateFinished;
+  GRXWriter *copiedWriter;
+  @synchronized(self) {
+    copiedWriter = _writer;
+  }
+  return copiedWriter ? copiedWriter.state : GRXWriterStateFinished;
 }
 
 - (void)setState:(GRXWriterState)state {
@@ -106,6 +110,7 @@
   @synchronized(self) {
     [self finishOutputWithError:errorOrNil];
     copiedWriter = _writer;
+    _writer = nil;
   }
   copiedWriter.state = GRXWriterStateFinished;
 }