allow engines to wait for url_files to arrive

if connection info (url, ip, etc.) is passed explicitly, the engine will not wait for the file.

If the file never arrives and the connection info was not specified manually, the app will abort.

This is primarily useful in batch-systems where engines might start before the controller has a chance to write connection files. (delay does not help in these cases, because it could be hours before jobs start)

IPython/parallel/apps/ipengineapp.py

@@ -24,6 +24,7 b' Authors:'
 import json
 import os
 import sys
+import time
 
 import zmq
 from zmq.eventloop import ioloop
@@ -43,7 +44,7 b' from IPython.parallel.engine.streamkernel import Kernel'
 from IPython.parallel.util import disambiguate_url
 
 from IPython.utils.importstring import import_item
-from IPython.utils.traitlets import Bool, Unicode, Dict, List
+from IPython.utils.traitlets import Bool, Unicode, Dict, List, Float
 
 
 #-----------------------------------------------------------------------------
@@ -143,6 +144,11 b' class IPEngineApp(BaseParallelApplication):'
         security directory of the cluster directory.  This location is
         resolved using the `profile` or `profile_dir` options.""",
         )
+    wait_for_url_file = Float(5, config=True,
+        help="""The maximum number of seconds to wait for url_file to exist.
+        This is useful for batch-systems and shared-filesystems where the
+        controller and engine are started at the same time and it
+        may take a moment for the controller to write the connector files.""")
 
     url_file_name = Unicode(u'ipcontroller-engine.json')
     log_url = Unicode('', config=True,
@@ -168,7 +174,7 b' class IPEngineApp(BaseParallelApplication):'
     #         config.Global.key_file = try_this
         
     def find_url_file(self):
-        """Set the key file.
+        """Set the url file.
 
         Here we don't try to actually see if it exists for is valid as that
         is hadled by the connection logic.
@@ -186,10 +192,28 b' class IPEngineApp(BaseParallelApplication):'
         config = self.config
         # print config
         self.find_url_file()
-
-        # if os.path.exists(config.Global.key_file) and config.Global.secure:
-        #     config.SessionFactory.exec_key = config.Global.key_file
+        
+        # was the url manually specified?
+        keys = set(self.config.EngineFactory.keys())
+        keys = keys.union(set(self.config.RegistrationFactory.keys()))
+        
+        if keys.intersection(set(['ip', 'url', 'port'])):
+            # Connection info was specified, don't wait for the file
+            url_specified = True
+            self.wait_for_url_file = 0
+        else:
+            url_specified = False
+
+        if self.wait_for_url_file and not os.path.exists(self.url_file):
+            self.log.warn("url_file %r not found"%self.url_file)
+            self.log.warn("Waiting up to %.1f seconds for it to arrive."%self.wait_for_url_file)
+            tic = time.time()
+            while not os.path.exists(self.url_file) and (time.time()-tic < self.wait_for_url_file):
+                # wait for url_file to exist, for up to 10 seconds
+                time.sleep(0.1)
+            
         if os.path.exists(self.url_file):
+            self.log.info("Loading url_file %r"%self.url_file)
             with open(self.url_file) as f:
                 d = json.loads(f.read())
                 for k,v in d.iteritems():
@@ -200,6 +224,10 b' class IPEngineApp(BaseParallelApplication):'
             d['url'] = disambiguate_url(d['url'], d['location'])
             config.EngineFactory.url = d['url']
             config.EngineFactory.location = d['location']
+        elif not url_specified:
+            self.log.critical("Fatal: url file never arrived: %s"%self.url_file)
+            self.exit(1)
+        
         
         try:
             exec_lines = config.Kernel.exec_lines

IPython/parallel/engine/engine.py

@@ -72,7 +72,7 b' class EngineFactory(RegistrationFactory):'
     def register(self):
         """send the registration_request"""
         
-        self.log.info("registering")
+        self.log.info("Registering with controller at %s"%self.url)
         content = dict(queue=self.ident, heartbeat=self.ident, control=self.ident)
         self.registrar.on_recv(self.complete_registration)
         # print (self.session.key)