Source code for

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"""For internal use only; no backwards-compatibility guarantees.

Concat Source, which reads the union of several other sources.

import bisect
import threading

from import iobase

[docs]class ConcatSource(iobase.BoundedSource): """For internal use only; no backwards-compatibility guarantees. A ``BoundedSource`` that can group a set of ``BoundedSources``. Primarily for internal use, use the ``apache_beam.Flatten`` transform to create the union of several reads. """ def __init__(self, sources): self._source_bundles = [source if isinstance(source, iobase.SourceBundle) else iobase.SourceBundle(None, source, None, None) for source in sources] @property def sources(self): return [s.source for s in self._source_bundles]
[docs] def estimate_size(self): return sum(s.source.estimate_size() for s in self._source_bundles)
[docs] def split( self, desired_bundle_size=None, start_position=None, stop_position=None): if start_position or stop_position: raise ValueError( 'Multi-level initial splitting is not supported. Expected start and ' 'stop positions to be None. Received %r and %r respectively.' % (start_position, stop_position)) for source in self._source_bundles: # We assume all sub-sources to produce bundles that specify weight using # the same unit. For example, all sub-sources may specify the size in # bytes as their weight. for bundle in source.source.split( desired_bundle_size, source.start_position, source.stop_position): yield bundle
[docs] def get_range_tracker(self, start_position=None, stop_position=None): if start_position is None: start_position = (0, None) if stop_position is None: stop_position = (len(self._source_bundles), None) return ConcatRangeTracker( start_position, stop_position, self._source_bundles)
[docs] def read(self, range_tracker): start_source, _ = range_tracker.start_position() stop_source, stop_pos = range_tracker.stop_position() if stop_pos is not None: stop_source += 1 for source_ix in range(start_source, stop_source): if not range_tracker.try_claim((source_ix, None)): break for record in self._source_bundles[source_ix] range_tracker.sub_range_tracker(source_ix)): yield record
[docs] def default_output_coder(self): if self._source_bundles: # Getting coder from the first sub-sources. This assumes all sub-sources # to produce the same coder. return self._source_bundles[0].source.default_output_coder() else: return super(ConcatSource, self).default_output_coder()
[docs]class ConcatRangeTracker(iobase.RangeTracker): """For internal use only; no backwards-compatibility guarantees. Range tracker for ConcatSource""" def __init__(self, start, end, source_bundles): """Initializes ``ConcatRangeTracker`` Args: start: start position, a tuple of (source_index, source_position) end: end position, a tuple of (source_index, source_position) source_bundles: the list of source bundles in the ConcatSource """ super(ConcatRangeTracker, self).__init__() self._start = start self._end = end self._source_bundles = source_bundles self._lock = threading.RLock() # Lazily-initialized list of RangeTrackers corresponding to each source. self._range_trackers = [None] * len(source_bundles) # The currently-being-iterated-over (and latest claimed) source. self._claimed_source_ix = self._start[0] # Now compute cumulative progress through the sources for converting # between global fractions and fractions within specific sources. # TODO(robertwb): Implement fraction-at-position to properly scale # partial start and end sources. # Note, however, that in practice splits are typically on source # boundaries anyways. last = end[0] if end[1] is None else end[0] + 1 self._cumulative_weights = ( [0] * start[0] + self._compute_cumulative_weights(source_bundles[start[0]:last]) + [1] * (len(source_bundles) - last - start[0])) @staticmethod def _compute_cumulative_weights(source_bundles): # Two adjacent sources must differ so that they can be uniquely # identified by a single global fraction. Let min_diff be the # smallest allowable difference between sources. min_diff = 1e-5 # For the computation below, we need weights for all sources. # Substitute average weights for those whose weights are # unspecified (or 1.0 for everything if none are known). known = [s.weight for s in source_bundles if s.weight is not None] avg = sum(known) / len(known) if known else 1.0 weights = [s.weight or avg for s in source_bundles] # Now compute running totals of the percent done upon reaching # each source, with respect to the start and end positions. # E.g. if the weights were [100, 20, 3] we would produce # [0.0, 100/123, 120/123, 1.0] total = float(sum(weights)) running_total = [0] for w in weights: running_total.append( max(min_diff, min(1, running_total[-1] + w / total))) running_total[-1] = 1 # In case of rounding error. # There are issues if, due to rouding error or greatly differing sizes, # two adjacent running total weights are equal. Normalize this things so # that this never happens. for k in range(1, len(running_total)): if running_total[k] == running_total[k - 1]: for j in range(k): running_total[j] *= (1 - min_diff) return running_total
[docs] def start_position(self): return self._start
[docs] def stop_position(self): return self._end
[docs] def try_claim(self, pos): source_ix, source_pos = pos with self._lock: if source_ix > self._end[0]: return False elif source_ix == self._end[0] and self._end[1] is None: return False else: assert source_ix >= self._claimed_source_ix self._claimed_source_ix = source_ix if source_pos is None: return True else: return self.sub_range_tracker(source_ix).try_claim(source_pos)
[docs] def try_split(self, pos): source_ix, source_pos = pos with self._lock: if source_ix < self._claimed_source_ix: # Already claimed. return None elif source_ix > self._end[0]: # After end. return None elif source_ix == self._end[0] and self._end[1] is None: # At/after end. return None else: if source_ix > self._claimed_source_ix: # Prefer to split on even boundary. split_pos = None ratio = self._cumulative_weights[source_ix] else: # Split the current subsource. split = self.sub_range_tracker(source_ix).try_split( source_pos) if not split: return None split_pos, frac = split ratio = self.local_to_global(source_ix, frac) self._end = source_ix, split_pos self._cumulative_weights = [min(w / ratio, 1) for w in self._cumulative_weights] return (source_ix, split_pos), ratio
[docs] def set_current_position(self, pos): raise NotImplementedError('Should only be called on sub-trackers')
[docs] def position_at_fraction(self, fraction): source_ix, source_frac = self.global_to_local(fraction) last = self._end[0] if self._end[1] is None else self._end[0] + 1 if source_ix == last: return (source_ix, None) else: return (source_ix, self.sub_range_tracker(source_ix).position_at_fraction( source_frac))
[docs] def fraction_consumed(self): with self._lock: return self.local_to_global( self._claimed_source_ix, self.sub_range_tracker(self._claimed_source_ix) .fraction_consumed())
[docs] def local_to_global(self, source_ix, source_frac): cw = self._cumulative_weights # The global fraction is the fraction to source_ix plus some portion of # the way towards the next source. return cw[source_ix] + source_frac * (cw[source_ix + 1] - cw[source_ix])
[docs] def global_to_local(self, frac): if frac == 1: last = self._end[0] if self._end[1] is None else self._end[0] + 1 return (last, None) else: cw = self._cumulative_weights # Find the last source that starts at or before frac. source_ix = bisect.bisect(cw, frac) - 1 # Return this source, converting what's left of frac after starting # this source into a value in [0.0, 1.0) representing how far we are # towards the next source. return (source_ix, (frac - cw[source_ix]) / (cw[source_ix + 1] - cw[source_ix]))
[docs] def sub_range_tracker(self, source_ix): assert self._start[0] <= source_ix <= self._end[0] if self._range_trackers[source_ix] is None: with self._lock: if self._range_trackers[source_ix] is None: source = self._source_bundles[source_ix] if source_ix == self._start[0] and self._start[1] is not None: start = self._start[1] else: start = source.start_position if source_ix == self._end[0] and self._end[1] is not None: stop = self._end[1] else: stop = source.stop_position self._range_trackers[source_ix] = source.source.get_range_tracker( start, stop) return self._range_trackers[source_ix]