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https://github.com/ceph/ceph
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79607eed3c
Exception objects don't contain the traceback of where they were raised from (to avoid cyclic data structures wrecking gc and causing mem leaks), so the singular "raise obj" form creates a new traceback from the current execution location, thus losing the original location of the error. Gevent explicitly wants to throw away the traceback, to release any objects the greenlet may still be referring to, closing files, releasing locks etc. In this case, we think it's safe, so stash the exception info away in a holder object, and resurrect it on the other side of the results queue. http://stackoverflow.com/questions/9268916/how-to-capture-a-traceback-in-gevent This can be reproduced easily with from teuthology.parallel import parallel def f(): raise RuntimeError("bork") with parallel() as p: p.spawn(f) and looking at the resulting traceback with and without this change.
116 lines
3.0 KiB
Python
116 lines
3.0 KiB
Python
import logging
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import sys
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import gevent.pool
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import gevent.queue
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log = logging.getLogger(__name__)
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class ExceptionHolder(object):
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def __init__(self, exc_info):
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self.exc_info = exc_info
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def capture_traceback(func, *args, **kwargs):
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"""
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Utility function to capture tracebacks of any exception func
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raises.
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"""
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try:
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return func(*args, **kwargs)
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except Exception:
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return ExceptionHolder(sys.exc_info())
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def resurrect_traceback(exc):
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if isinstance(exc, ExceptionHolder):
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exc_info = exc.exc_info
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elif isinstance(exc, BaseException):
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print type(exc)
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exc_info = (type(exc), exc, None)
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else:
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return
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raise exc_info[0], exc_info[1], exc_info[2]
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class parallel(object):
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"""
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This class is a context manager for running functions in parallel.
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You add functions to be run with the spawn method::
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with parallel() as p:
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for foo in bar:
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p.spawn(quux, foo, baz=True)
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You can iterate over the results (which are in arbitrary order)::
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with parallel() as p:
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for foo in bar:
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p.spawn(quux, foo, baz=True)
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for result in p:
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print result
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If one of the spawned functions throws an exception, it will be thrown
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when iterating over the results, or when the with block ends.
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At the end of the with block, the main thread waits until all
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spawned functions have completed, or, if one exited with an exception,
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kills the rest and raises the exception.
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"""
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def __init__(self):
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self.group = gevent.pool.Group()
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self.results = gevent.queue.Queue()
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self.count = 0
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self.any_spawned = False
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self.iteration_stopped = False
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def spawn(self, func, *args, **kwargs):
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self.count += 1
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self.any_spawned = True
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greenlet = self.group.spawn(capture_traceback, func, *args, **kwargs)
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greenlet.link(self._finish)
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def __enter__(self):
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return self
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def __exit__(self, type_, value, traceback):
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if value is not None:
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self.group.kill(block=True)
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return False
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try:
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# raises if any greenlets exited with an exception
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for result in self:
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log.debug('result is %s', repr(result))
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pass
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except:
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self.group.kill(block=True)
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raise
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return True
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def __iter__(self):
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return self
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def next(self):
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if not self.any_spawned or self.iteration_stopped:
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raise StopIteration()
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result = self.results.get()
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try:
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resurrect_traceback(result)
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except StopIteration:
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self.iteration_stopped = True
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raise
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return result
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def _finish(self, greenlet):
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if greenlet.successful():
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self.results.put(greenlet.value)
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else:
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self.results.put(greenlet.exception)
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self.count -= 1
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if self.count <= 0:
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self.results.put(StopIteration())
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