def append(self, filename):
newblknum = self.length(filename)
blk = BlockId(filename, newblknum)
b = bytearray(self.blocksize)
try:
f = self.getFile(blk.fileName())
f.seek(blk.number() * self.blocksize)
f.write(b)
except IOError:
raise RuntimeError("cannot append block" + blk)
return blk
class LogIterator:
#
# * Creates an iterator for the records in the log file,
# * positioned after the last log record.
#
def __init__(self, fm, blk):
self.fm = fm
self.blk = blk
self.currentpos = 0
self.boundary = 0
b = bytearray(fm.blockSize())
self.p = Page(b)
self.moveToBlock(blk)
#
# * Determines if the current log record
# * is the earliest record in the log file.
# * @return true if there is an earlier record
#
def hasNext(self):
return self.currentpos < self.fm.blockSize() or self.blk.number() > 0
#
# * Moves to the next log record in the block.
# * If there are no more log records in the block,
# * then move to the previous block
# * and return the log record from there.
# * @return the next earliest log record
#
def next(self):
if self.currentpos == self.fm.blockSize():
self.blk = BlockId(self.blk.fileName(), self.blk.number() - 1)
self.moveToBlock(self.blk)
rec = self.p.getBytes(self.currentpos)
self.currentpos += Integer.BYTES + len(rec)
return rec
#
# * Moves to the specified log block
# * and positions it at the first record in that block
# * (i.e., the most recent one).
#
def moveToBlock(self, blk):
self.fm.read(blk, self.p)
self.boundary = self.p.getInt(0)
self.currentpos = self.boundary