Lock GRPCCall in GRPCAuthorizatioProtocol

src/objective-c/GRPCClient/GRPCCall.m

@@ -461,11 +461,13 @@ const char *kCFStreamVarName = "grpc_cfstream";
 }
 
 - (void)cancel {
+  @synchronized (self) {
     if (!self.isWaitingForToken) {
       [self cancelCall];
     } else {
       self.isWaitingForToken = NO;
     }
+  }
   [self
       maybeFinishWithError:[NSError
                                errorWithDomain:kGRPCErrorDomain
@@ -779,8 +781,11 @@ const char *kCFStreamVarName = "grpc_cfstream";
     _callOptions = callOptions;
   }
   if (_callOptions.authTokenProvider != nil) {
+    @synchronized (self) {
       self.isWaitingForToken = YES;
+    }
     [self.tokenProvider getTokenWithHandler:^(NSString *token) {
+      @synchronized (self) {
         if (self.isWaitingForToken) {
           if (token) {
             self->_fetchedOauth2AccessToken = [token copy];
@@ -788,6 +793,7 @@ const char *kCFStreamVarName = "grpc_cfstream";
           [self startCallWithWriteable:writeable];
           self.isWaitingForToken = NO;
         }
+      }
     }];
   } else {
     [self startCallWithWriteable:writeable];