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Viewing changes to loggerhead/changecache.py

merge my less-file-change-access branch, which mainly only computes expensive
information (the set of files changed in a revision) when it's actually needed,
but also a bunch of other streamlining and efficiency improvements.

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Lines of Context:
loggerhead/changecache.py
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        self.flush()
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class FileChangeCache(object):
 
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    def __init__(self, history, cache_path):
 
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        self.history = history
 
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        self.log = history.log
 
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        if not os.path.exists(cache_path):
 
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            os.mkdir(cache_path)
 
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        self._changes_filename = os.path.join(cache_path, 'filechanges')
 
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        # use a lockfile since the cache folder could be shared across
 
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        # different processes.
 
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        self._lock = LockFile(os.path.join(cache_path, 'filechange-lock'))
 
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        self._closed = False
 
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    @with_lock
 
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    def close(self):
 
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        self.log.debug('Closing cache file.')
 
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        self._closed = True
 
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    @with_lock
 
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    def closed(self):
 
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        return self._closed
 
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    @with_lock
 
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    def flush(self):
 
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        pass
 
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    @with_lock
 
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    def get_file_changes(self, entries):
 
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        cache = shelve.open(self._changes_filename, 'c', protocol=2)
 
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        try:
 
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            out = []
 
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            missing_entries = []
 
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            missing_entry_indices = []
 
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            for entry in entries:
 
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                changes = cache.get(entry.revid)
 
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                if changes is not None:
 
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                    out.append(changes)
 
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                else:
 
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                    missing_entries.append(entry)
 
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                    missing_entry_indices.append(len(out))
 
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                    out.append(None)
 
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            missing_changes = self.history.get_file_changes_uncached(missing_entries)
 
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            for i, entry, changes in zip(
 
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                missing_entry_indices, missing_entries, missing_changes):
 
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                cache[entry.revid] = out[i] = changes
 
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            return out
 
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        finally:
 
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            cache.close()