Check for pids when listing nbserver processes

IPython/html/notebookapp.py

@@ -74,6 +74,7 b' from IPython.kernel.zmq.session import default_secure, Session'
 from IPython.nbformat.sign import NotebookNotary
 from IPython.utils.importstring import import_item
 from IPython.utils import submodule
+from IPython.utils.process import check_pid
 from IPython.utils.traitlets import (
     Dict, Unicode, Integer, List, Bool, Bytes, Instance,
     DottedObjectName, TraitError,
@@ -844,6 +845,7 b' class NotebookApp(BaseIPythonApplication):'
                 'secure': bool(self.certfile),
                 'base_url': self.base_url,
                 'notebook_dir': os.path.abspath(self.notebook_dir),
+                'pid': os.getpid()
                }
 
     def write_server_info_file(self):
@@ -917,8 +919,17 b" def list_running_servers(profile='default'):"
     for file in os.listdir(pd.security_dir):
         if file.startswith('nbserver-'):
             with io.open(os.path.join(pd.security_dir, file), encoding='utf-8') as f:
-                yield json.load(f)
+                info = json.load(f)
 
+            # Simple check whether that process is really still running
+            if check_pid(info['pid']):
+                yield info
+            else:
+                # If the process has died, try to delete its info file
+                try:
+                    os.unlink(file)
+                except OSError:
+                    pass  # TODO: This should warn or log or something
 #-----------------------------------------------------------------------------
 # Main entry point
 #-----------------------------------------------------------------------------

IPython/utils/_process_posix.py

@@ -16,6 +16,8 b' This file is only meant to be imported by process.py, not by end-users.'
 from __future__ import print_function
 
 # Stdlib
+import errno
+import os
 import subprocess as sp
 import sys
 
@@ -209,5 +211,15 b' class ProcessHandler(object):'
 # (ls is a good example) that makes them hard.
 system = ProcessHandler().system
 
-
-
+def check_pid(pid):
+    try:
+        os.kill(pid, 0)
+    except OSError as err:
+        if err.errno == errno.ESRCH:
+            return False
+        elif err.errno == errno.EPERM:
+            # Don't have permission to signal the process - probably means it exists
+            return True
+        raise
+    else:
+        return True

IPython/utils/_process_win32.py

@@ -185,3 +185,8 b' try:'
         return result
 except AttributeError:
     arg_split = py_arg_split
+
+def check_pid(pid):
+    # OpenProcess returns 0 if no such process (of ours) exists
+    # positive int otherwise
+    return bool(ctypes.windll.kernel32.OpenProcess(1,0,pid))

IPython/utils/process.py

@@ -21,11 +21,11 b' import sys'
 
 # Our own
 if sys.platform == 'win32':
-    from ._process_win32 import _find_cmd, system, getoutput, arg_split
+    from ._process_win32 import _find_cmd, system, getoutput, arg_split, check_pid
 elif sys.platform == 'cli':
     from ._process_cli import _find_cmd, system, getoutput, arg_split
 else:
-    from ._process_posix import _find_cmd, system, getoutput, arg_split
+    from ._process_posix import _find_cmd, system, getoutput, arg_split, check_pid
 
 from ._process_common import getoutputerror, get_output_error_code, process_handler
 from . import py3compat