Ensure that pause() and unpause() conform to documentation.

These will now block the caller until they are handled by the queue
thread.

Fixes #2877

playhouse/sqliteq.py

@@ -113,6 +113,7 @@ def fetchone(self):
             return None
 
 SHUTDOWN = StopIteration
+QUERY = object()
 PAUSE = object()
 UNPAUSE = object()
 
@@ -143,30 +144,34 @@ def run(self):
                 self.database._state.reset()
 
     def wait_unpause(self):
-        obj = self.queue.get()
-        if obj is UNPAUSE:
+        op, obj = self.queue.get()
+        if op is UNPAUSE:
             logger.info('writer unpaused - reconnecting to database.')
+            obj.set()
             return True
-        elif obj is SHUTDOWN:
+        elif op is SHUTDOWN:
             raise ShutdownException()
-        elif obj is PAUSE:
+        elif op is PAUSE:
             logger.error('writer received pause, but is already paused.')
+            obj.set()
         else:
             obj.set_result(None, WriterPaused())
             logger.warning('writer paused, not handling %s', obj)
 
     def loop(self, conn):
-        obj = self.queue.get()
-        if isinstance(obj, AsyncCursor):
+        op, obj = self.queue.get()
+        if op is QUERY:
             self.execute(obj)
-        elif obj is PAUSE:
+        elif op is PAUSE:
             logger.info('writer paused - closing database connection.')
             self.database._close(conn)
             self.database._state.reset()
+            obj.set()
             return
-        elif obj is UNPAUSE:
+        elif op is UNPAUSE:
             logger.error('writer received unpause, but is already running.')
-        elif obj is SHUTDOWN:
+            obj.set()
+        elif op is SHUTDOWN:
             raise ShutdownException()
         else:
             logger.error('writer received unsupported object: %s', obj)
@@ -255,7 +260,7 @@ def execute_sql(self, sql, params=None, commit=None, timeout=None):
             sql=sql,
             params=params,
             timeout=self._results_timeout if timeout is None else timeout)
-        self._write_queue.put(cursor)
+        self._write_queue.put((QUERY, cursor))
         return cursor
 
     def start(self):
@@ -276,7 +281,7 @@ def stop(self):
         with self._qlock:
             if self._is_stopped:
                 return False
-            self._write_queue.put(SHUTDOWN)
+            self._write_queue.put((SHUTDOWN, None))
             self._writer.join()
             self._is_stopped = True
             return True
@@ -286,10 +291,14 @@ def is_stopped(self):
             return self._is_stopped
 
     def pause(self):
-        self._write_queue.put(PAUSE)
+        evt = self._thread_helper.event()
+        self._write_queue.put((PAUSE, evt))
+        evt.wait()
 
     def unpause(self):
-        self._write_queue.put(UNPAUSE)
+        evt = self._thread_helper.event()
+        self._write_queue.put((UNPAUSE, evt))
+        evt.wait()
 
     def __unsupported__(self, *args, **kwargs):
         raise ValueError('This method is not supported by %r.' % type(self))