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127 lines
4.8 KiB
Python
127 lines
4.8 KiB
Python
2 years ago
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"""Win32 compatibility utilities."""
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# -----------------------------------------------------------------------------
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# Copyright (C) PyZMQ Developers
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# Distributed under the terms of the Modified BSD License.
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# -----------------------------------------------------------------------------
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import os
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from typing import Any, Callable, Optional
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class allow_interrupt:
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"""Utility for fixing CTRL-C events on Windows.
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On Windows, the Python interpreter intercepts CTRL-C events in order to
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translate them into ``KeyboardInterrupt`` exceptions. It (presumably)
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does this by setting a flag in its "console control handler" and
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checking it later at a convenient location in the interpreter.
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However, when the Python interpreter is blocked waiting for the ZMQ
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poll operation to complete, it must wait for ZMQ's ``select()``
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operation to complete before translating the CTRL-C event into the
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``KeyboardInterrupt`` exception.
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The only way to fix this seems to be to add our own "console control
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handler" and perform some application-defined operation that will
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unblock the ZMQ polling operation in order to force ZMQ to pass control
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back to the Python interpreter.
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This context manager performs all that Windows-y stuff, providing you
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with a hook that is called when a CTRL-C event is intercepted. This
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hook allows you to unblock your ZMQ poll operation immediately, which
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will then result in the expected ``KeyboardInterrupt`` exception.
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Without this context manager, your ZMQ-based application will not
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respond normally to CTRL-C events on Windows. If a CTRL-C event occurs
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while blocked on ZMQ socket polling, the translation to a
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``KeyboardInterrupt`` exception will be delayed until the I/O completes
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and control returns to the Python interpreter (this may never happen if
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you use an infinite timeout).
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A no-op implementation is provided on non-Win32 systems to avoid the
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application from having to conditionally use it.
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Example usage:
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.. sourcecode:: python
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def stop_my_application():
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# ...
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with allow_interrupt(stop_my_application):
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# main polling loop.
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In a typical ZMQ application, you would use the "self pipe trick" to
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send message to a ``PAIR`` socket in order to interrupt your blocking
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socket polling operation.
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In a Tornado event loop, you can use the ``IOLoop.stop`` method to
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unblock your I/O loop.
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"""
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def __init__(self, action: Optional[Callable[[], Any]] = None) -> None:
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"""Translate ``action`` into a CTRL-C handler.
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``action`` is a callable that takes no arguments and returns no
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value (returned value is ignored). It must *NEVER* raise an
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exception.
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If unspecified, a no-op will be used.
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"""
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if os.name != "nt":
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return
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self._init_action(action)
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def _init_action(self, action):
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from ctypes import WINFUNCTYPE, windll
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from ctypes.wintypes import BOOL, DWORD
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kernel32 = windll.LoadLibrary('kernel32')
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# <http://msdn.microsoft.com/en-us/library/ms686016.aspx>
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PHANDLER_ROUTINE = WINFUNCTYPE(BOOL, DWORD)
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SetConsoleCtrlHandler = (
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self._SetConsoleCtrlHandler
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) = kernel32.SetConsoleCtrlHandler
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SetConsoleCtrlHandler.argtypes = (PHANDLER_ROUTINE, BOOL)
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SetConsoleCtrlHandler.restype = BOOL
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if action is None:
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action = lambda: None
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self.action = action
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@PHANDLER_ROUTINE
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def handle(event):
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if event == 0: # CTRL_C_EVENT
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action()
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# Typical C implementations would return 1 to indicate that
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# the event was processed and other control handlers in the
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# stack should not be executed. However, that would
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# prevent the Python interpreter's handler from translating
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# CTRL-C to a `KeyboardInterrupt` exception, so we pretend
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# that we didn't handle it.
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return 0
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self.handle = handle
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def __enter__(self):
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"""Install the custom CTRL-C handler."""
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if os.name != "nt":
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return
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result = self._SetConsoleCtrlHandler(self.handle, 1)
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if result == 0:
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# Have standard library automatically call `GetLastError()` and
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# `FormatMessage()` into a nice exception object :-)
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raise OSError()
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def __exit__(self, *args):
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"""Remove the custom CTRL-C handler."""
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if os.name != "nt":
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return
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result = self._SetConsoleCtrlHandler(self.handle, 0)
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if result == 0:
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# Have standard library automatically call `GetLastError()` and
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# `FormatMessage()` into a nice exception object :-)
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raise OSError()
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