Add state transitions to GRPCCall

src/objective-c/GRPCClient/GRPCCall.m

@@ -136,6 +136,10 @@ NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
 #pragma mark Finish
 
 - (void)finishWithError:(NSError *)errorOrNil {
+  @synchronized(self) {
+    _state = GRXWriterStateFinished;
+  }
+
   // If the call isn't retained anywhere else, it can be deallocated now.
   _retainSelf = nil;
 
@@ -342,6 +346,10 @@ NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
 #pragma mark GRXWriter implementation
 
 - (void)startWithWriteable:(id<GRXWriteable>)writeable {
+  @synchronized(self) {
+    _state = GRXWriterStateStarted;
+  }
+
   // Create a retain cycle so that this instance lives until the RPC finishes (or is cancelled).
   // This makes RPCs in which the call isn't externally retained possible (as long as it is started
   // before being autoreleased).
@@ -375,6 +383,7 @@ NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
 }
 
 - (void)setState:(GRXWriterState)newState {
+  @synchronized(self) {
     // Manual transitions are only allowed from the started or paused states.
     if (_state == GRXWriterStateNotStarted || _state == GRXWriterStateFinished) {
       return;
@@ -401,5 +410,6 @@ NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
         return;
     }
   }
+}
 
 @end