compound.py 文件源码

def __init__(self, dbfile, use_mmap=True, basepos=0):
        self._file = dbfile
        self.is_closed = False

        # Seek to the end to get total file size (to check if mmap is OK)
        dbfile.seek(0, os.SEEK_END)
        filesize = self._file.tell()
        dbfile.seek(basepos)

        self._diroffset = self._file.read_long()
        self._dirlength = self._file.read_int()
        self._file.seek(self._diroffset)
        self._dir = self._file.read_pickle()
        self._options = self._file.read_pickle()
        self._locks = {}
        self._source = None

        use_mmap = (
            use_mmap
            and hasattr(self._file, "fileno")  # check file is a real file
            and filesize < sys.maxsize  # check fit on 32-bit Python
        )
        if mmap and use_mmap:
            # Try to open the entire segment as a memory-mapped object
            try:
                fileno = self._file.fileno()
                self._source = mmap.mmap(fileno, 0, access=mmap.ACCESS_READ)
            except (mmap.error, OSError):
                e = sys.exc_info()[1]
                # If we got an error because there wasn't enough memory to
                # open the map, ignore it and fall through, we'll just use the
                # (slower) "sub-file" implementation
                if e.errno == errno.ENOMEM:
                    pass
                else:
                    raise
            else:
                # If that worked, we can close the file handle we were given
                self._file.close()
                self._file = None