Corrects handling of status during bidi call orchestration.

- Ensures that invalid status are raised as exceptions
- Ensures that exceptions during the write thread are bubbled up to the starting
  thread

Also - improves the debug messages during the BiDi calls

src/ruby/lib/grpc/generic/bidi_call.rb

@@ -78,13 +78,11 @@ module GRPC
     # @param requests the Enumerable of requests to send
     # @return an Enumerator of requests to yield
     def run_on_client(requests, &blk)
-      enq_th = start_write_loop(requests)
-      loop_th = start_read_loop
+      @enq_th = start_write_loop(requests)
+      @loop_th = start_read_loop
       replies = each_queued_msg
       return replies if blk.nil?
       replies.each { |r| blk.call(r) }
-      enq_th.join
-      loop_th.join
     end
 
     # Begins orchestration of the Bidi stream for a server generating replies.
@@ -100,10 +98,8 @@ module GRPC
     # @param gen_each_reply [Proc] generates the BiDi stream replies.
     def run_on_server(gen_each_reply)
       replys = gen_each_reply.call(each_queued_msg)
-      enq_th = start_write_loop(replys, is_client: false)
-      loop_th = start_read_loop
-      loop_th.join
-      enq_th.join
+      @enq_th = start_write_loop(replys, is_client: false)
+      @loop_th = start_read_loop
     end
 
     private
@@ -122,10 +118,13 @@ module GRPC
         logger.debug("each_queued_msg: msg##{count}")
         count += 1
         req = @readq.pop
+        logger.debug("each_queued_msg: req = #{req}")
         throw req if req.is_a? StandardError
         break if req.equal?(END_OF_READS)
         yield req
       end
+      @loop_th.join
+      @enq_th.join
     end
 
     # during bidi-streaming, read the requests to send from a separate thread
@@ -136,20 +135,23 @@ module GRPC
         begin
           count = 0
           requests.each do |req|
+            logger.debug("bidi-write_loop: #{count}")
             count += 1
             payload = @marshal.call(req)
             @call.run_batch(@cq, write_tag, INFINITE_FUTURE,
                             SEND_MESSAGE => payload)
           end
           if is_client
-            logger.debug("bidi-client: sent #{count} reqs, waiting to finish")
-            @call.run_batch(@cq, write_tag, INFINITE_FUTURE,
-                            SEND_CLOSE_FROM_CLIENT => nil,
-                            RECV_STATUS_ON_CLIENT => nil)
+            logger.debug("bidi-write-loop: sent #{count}, waiting to finish")
+            batch_result = @call.run_batch(@cq, write_tag, INFINITE_FUTURE,
+                                           SEND_CLOSE_FROM_CLIENT => nil,
+                                           RECV_STATUS_ON_CLIENT => nil)
+            batch_result.check_status
           end
         rescue StandardError => e
-          logger.warn('bidi: write_loop failed')
+          logger.warn('bidi-write_loop: failed')
           logger.warn(e)
+          raise e
         end
       end
     end
@@ -163,7 +165,7 @@ module GRPC
 
           # queue the initial read before beginning the loop
           loop do
-            logger.debug("waiting for read #{count}")
+            logger.debug("bidi-read_loop: #{count}")
             count += 1
             # TODO: ensure metadata is read if available, currently it's not
             batch_result = @call.run_batch(@cq, read_tag, INFINITE_FUTURE,
@@ -171,7 +173,7 @@ module GRPC
             # handle the next message
             if batch_result.message.nil?
               @readq.push(END_OF_READS)
-              logger.debug('done reading!')
+              logger.debug('bidi-read-loop: done reading!')
               break
             end