avoid ctypes import in parentpoller when unnecessary

IPython/zmq/parentpoller.py

@@ -1,131 +1,136 b''
 # Standard library imports.
-import ctypes
+try:
+    import ctypes
+except:
+    ctypes = None
 import os
 import platform
 import time
 from thread import interrupt_main
 from threading import Thread
 
 from IPython.utils.warn import warn
 
 
 class ParentPollerUnix(Thread):
     """ A Unix-specific daemon thread that terminates the program immediately
     when the parent process no longer exists.
     """
 
     def __init__(self):
         super(ParentPollerUnix, self).__init__()
         self.daemon = True
 
     def run(self):
         # We cannot use os.waitpid because it works only for child processes.
         from errno import EINTR
         while True:
             try:
                 if os.getppid() == 1:
                     os._exit(1)
                 time.sleep(1.0)
             except OSError, e:
                 if e.errno == EINTR:
                     continue
                 raise
 
 
 class ParentPollerWindows(Thread):
     """ A Windows-specific daemon thread that listens for a special event that
     signals an interrupt and, optionally, terminates the program immediately
     when the parent process no longer exists.
     """
 
     def __init__(self, interrupt_handle=None, parent_handle=None):
         """ Create the poller. At least one of the optional parameters must be
         provided.
 
         Parameters:
         -----------
         interrupt_handle : HANDLE (int), optional
             If provided, the program will generate a Ctrl+C event when this
             handle is signaled.
 
         parent_handle : HANDLE (int), optional
             If provided, the program will terminate immediately when this
             handle is signaled.
         """
         assert(interrupt_handle or parent_handle)
         super(ParentPollerWindows, self).__init__()
+        if ctypes is None:
+            raise ImportError("ParentPollerWindows requires ctypes")
         self.daemon = True
         self.interrupt_handle = interrupt_handle
         self.parent_handle = parent_handle
 
     @staticmethod
     def create_interrupt_event():
         """ Create an interrupt event handle.
 
         The parent process should use this static method for creating the
         interrupt event that is passed to the child process. It should store
         this handle and use it with ``send_interrupt`` to interrupt the child
         process.
         """
         # Create a security attributes struct that permits inheritance of the
         # handle by new processes.
         # FIXME: We can clean up this mess by requiring pywin32 for IPython.
         class SECURITY_ATTRIBUTES(ctypes.Structure):
             _fields_ = [ ("nLength", ctypes.c_int),
                          ("lpSecurityDescriptor", ctypes.c_void_p),
                          ("bInheritHandle", ctypes.c_int) ]
         sa = SECURITY_ATTRIBUTES()
         sa_p = ctypes.pointer(sa)
         sa.nLength = ctypes.sizeof(SECURITY_ATTRIBUTES)
         sa.lpSecurityDescriptor = 0
         sa.bInheritHandle = 1
 
         return ctypes.windll.kernel32.CreateEventA(
             sa_p,  # lpEventAttributes
             False, # bManualReset
             False, # bInitialState
             '')    # lpName
 
     @staticmethod
     def send_interrupt(interrupt_handle):
         """ Sends an interrupt event using the specified handle.
         """
         ctypes.windll.kernel32.SetEvent(interrupt_handle)
 
     def run(self):
         """ Run the poll loop. This method never returns.
         """
         from _subprocess import WAIT_OBJECT_0, INFINITE
 
         # Build the list of handle to listen on.
         handles = []
         if self.interrupt_handle:
             handles.append(self.interrupt_handle)
         if self.parent_handle:
             handles.append(self.parent_handle)
         arch = platform.architecture()[0]
         c_int = ctypes.c_int64 if arch.startswith('64') else ctypes.c_int
 
         # Listen forever.
         while True:
             result = ctypes.windll.kernel32.WaitForMultipleObjects(
                 len(handles),                            # nCount
                 (c_int * len(handles))(*handles),        # lpHandles
                 False,                                   # bWaitAll
                 INFINITE)                                # dwMilliseconds
 
             if WAIT_OBJECT_0 <= result < len(handles):
                 handle = handles[result - WAIT_OBJECT_0]
 
                 if handle == self.interrupt_handle:
                     interrupt_main()
 
                 elif handle == self.parent_handle:
                     os._exit(1)
             elif result < 0:
                 # wait failed, just give up and stop polling.
                 warn("""Parent poll failed.  If the frontend dies,
                 the kernel may be left running.  Please let us know
                 about your system (bitness, Python, etc.) at
                 [e-mail]""")
                 return