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# Copyright (C) 2011 Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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from __future__ import absolute_import
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class CatchingExceptionThread(threading.Thread):
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"""A thread that keeps track of exceptions.
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If an exception occurs during the thread execution, it's caught and
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re-raised when the thread is joined().
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def __init__(self, *args, **kwargs):
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# There are cases where the calling thread must wait, yet, if an
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# exception occurs, the event should be set so the caller is not
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# blocked. The main example is a calling thread that want to wait for
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# the called thread to be in a given state before continuing.
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sync_event = kwargs.pop('sync_event')
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# If the caller didn't pass a specific event, create our own
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sync_event = threading.Event()
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super(CatchingExceptionThread, self).__init__(*args, **kwargs)
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self.set_sync_event(sync_event)
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self.ignored_exceptions = None # see set_ignored_exceptions
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self.lock = threading.Lock()
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# compatibility thunk for python-2.4 and python-2.5...
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if sys.version_info < (2, 6):
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name = property(threading.Thread.getName, threading.Thread.setName)
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def set_sync_event(self, event):
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"""Set the ``sync_event`` event used to synchronize exception catching.
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When the thread uses an event to synchronize itself with another thread
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(setting it when the other thread can wake up from a ``wait`` call),
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the event must be set after catching an exception or the other thread
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Some threads require multiple events and should set the relevant one
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Note that the event should be initially cleared so the caller can
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wait() on him and be released when the thread set the event.
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Also note that the thread can use multiple events, setting them as it
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progress, while the caller can chose to wait on any of them. What
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matters is that there is always one event set so that the caller is
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always released when an exception is caught. Re-using the same event is
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therefore risky as the thread itself has no idea about which event the
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caller is waiting on. If the caller has already been released then a
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cleared event won't guarantee that the caller is still waiting on it.
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self.sync_event = event
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def switch_and_set(self, new):
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"""Switch to a new ``sync_event`` and set the current one.
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Using this method protects against race conditions while setting a new
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Note that this allows a caller to wait either on the old or the new
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event depending on whether it wants a fine control on what is happening
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:param new: The event that will become ``sync_event``
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try: # Always release the lock
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self.set_sync_event(new)
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# From now on, any exception will be synced with the new event
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# Unlucky, we couldn't set the new sync event, try restoring a
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self.set_sync_event(cur)
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# Setting the current ``sync_event`` will release callers waiting
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# on it, note that it will also be set in run() if an exception is
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def set_ignored_exceptions(self, ignored):
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"""Declare which exceptions will be ignored.
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:param ignored: Can be either:
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- None: all exceptions will be raised,
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- an exception class: the instances of this class will be ignored,
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- a tuple of exception classes: the instances of any class of the
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list will be ignored,
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- a callable: that will be passed the exception object
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and should return True if the exception should be ignored
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self.ignored_exceptions = None
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elif isinstance(ignored, (Exception, tuple)):
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self.ignored_exceptions = lambda e: isinstance(e, ignored)
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self.ignored_exceptions = ignored
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"""Overrides Thread.run to capture any exception."""
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self.sync_event.clear()
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super(CatchingExceptionThread, self).run()
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self.exception = sys.exc_info()
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# Make sure the calling thread is released
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self.sync_event.set()
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def join(self, timeout=None):
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"""Overrides Thread.join to raise any exception caught.
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Calling join(timeout=0) will raise the caught exception or return None
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if the thread is still alive.
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super(CatchingExceptionThread, self).join(timeout)
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if self.exception is not None:
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exc_class, exc_value, exc_tb = self.exception
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self.exception = None # The exception should be raised only once
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if (self.ignored_exceptions is None
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or not self.ignored_exceptions(exc_value)):
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# Raise non ignored exceptions
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raise exc_class, exc_value, exc_tb
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def pending_exception(self):
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"""Raise the caught exception.
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This does nothing if no exception occurred.
added
removed
bzrlib/cethread.py
