bind_kernel on a bound kernel is a no-op

IPython/parallel/__init__.py

@@ -20,6 +20,7 b' import warnings'
 
 import zmq
 
+from IPython.config.configurable import MultipleInstanceError
 from IPython.zmq import check_for_zmq
 
 if os.name == 'nt':
@@ -51,12 +52,23 b' def bind_kernel(**kwargs):'
     
     This function returns immediately.
     """
+    from IPython.zmq.ipkernel import IPKernelApp
     from IPython.parallel.apps.ipengineapp import IPEngineApp
+    
+    # first check for IPKernelApp, in which case this should be a no-op
+    # because there is already a bound kernel
+    if IPKernelApp.initialized() and isinstance(IPKernelApp._instance, IPKernelApp):
+        return
+    
     if IPEngineApp.initialized():
-        app = IPEngineApp.instance()
-    else:
-        raise RuntimeError("Must be called from an IPEngineApp instance")
+        try:
+            app = IPEngineApp.instance()
+        except MultipleInstanceError:
+            pass
+        else:
+            return app.bind_kernel(**kwargs)
+    
+    raise RuntimeError("bind_kernel be called from an IPEngineApp instance")
     
-    return app.bind_kernel(**kwargs)