Add support for reopening closed pipes with consistency guarantees

pipe_io_server/pipe_writer_thread.py

@@ -15,21 +15,29 @@ class PipeWriterThread(Thread):
         self._write_queue = Queue()
 
     def write(self, message):
-        self._write_queue.put(message, block=True)
+        self._write_queue.put(message, block=False)
 
     @terminate_process_on_failure
     def run(self):
-        try:
-            with open(self._pipe_path, 'wb') as pipe:
-                while True:
-                    message = self._write_queue.get(block=True)
-                    if message is None:
-                        self._stop_event.set()
-                        break
+        with self._open() as pipe:
+            while True:
+                message = self._write_queue.get(block=True)
+                if message is None:
+                    self._stop_event.set()
+                    break
+                try:
                     pipe.write(message + b'\n')
                     pipe.flush()
-        except BrokenPipeError:
-            self._stop_event.set()
+                except BrokenPipeError:
+                    try:  # pipe was reopened, close() flushed the message
+                        pipe.close()
+                    except BrokenPipeError:  # close() discarded the message
+                        # TODO: a message is lost here, implement thread safe, blocking deque
+                        pass
+                    pipe = self._open()
+
+    def _open(self):
+        return open(self._pipe_path, 'wb')
 
     def stop(self):
         self.unblock()