119 lines
4.6 KiB
Python
119 lines
4.6 KiB
Python
import asyncio
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import typing
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from lbry.wallet.server.util import chunks, class_logger
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if typing.TYPE_CHECKING:
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from lbry.wallet.server.daemon import LBCDaemon
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from lbry.wallet.server.coin import Coin
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class Prefetcher:
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"""Prefetches blocks (in the forward direction only)."""
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def __init__(self, daemon: 'LBCDaemon', coin: 'Coin', blocks_event: asyncio.Event):
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self.logger = class_logger(__name__, self.__class__.__name__)
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self.daemon = daemon
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self.coin = coin
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self.blocks_event = blocks_event
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self.blocks = []
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self.caught_up = False
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# Access to fetched_height should be protected by the semaphore
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self.fetched_height = None
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self.semaphore = asyncio.Semaphore()
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self.refill_event = asyncio.Event()
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# The prefetched block cache size. The min cache size has
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# little effect on sync time.
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self.cache_size = 0
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self.min_cache_size = 10 * 1024 * 1024
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# This makes the first fetch be 10 blocks
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self.ave_size = self.min_cache_size // 10
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self.polling_delay = 0.5
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async def main_loop(self, bp_height):
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"""Loop forever polling for more blocks."""
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await self.reset_height(bp_height)
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try:
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while True:
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# Sleep a while if there is nothing to prefetch
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await self.refill_event.wait()
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if not await self._prefetch_blocks():
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await asyncio.sleep(self.polling_delay)
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finally:
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self.logger.info("block pre-fetcher is shutting down")
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def get_prefetched_blocks(self):
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"""Called by block processor when it is processing queued blocks."""
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blocks = self.blocks
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self.blocks = []
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self.cache_size = 0
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self.refill_event.set()
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return blocks
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async def reset_height(self, height):
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"""Reset to prefetch blocks from the block processor's height.
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Used in blockchain reorganisations. This coroutine can be
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called asynchronously to the _prefetch_blocks coroutine so we
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must synchronize with a semaphore.
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"""
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async with self.semaphore:
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self.blocks.clear()
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self.cache_size = 0
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self.fetched_height = height
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self.refill_event.set()
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daemon_height = await self.daemon.height()
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behind = daemon_height - height
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if behind > 0:
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self.logger.info(f'catching up to daemon height {daemon_height:,d} '
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f'({behind:,d} blocks behind)')
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else:
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self.logger.info(f'caught up to daemon height {daemon_height:,d}')
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async def _prefetch_blocks(self):
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"""Prefetch some blocks and put them on the queue.
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Repeats until the queue is full or caught up.
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"""
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daemon = self.daemon
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daemon_height = await daemon.height()
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async with self.semaphore:
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while self.cache_size < self.min_cache_size:
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# Try and catch up all blocks but limit to room in cache.
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# Constrain fetch count to between 0 and 500 regardless;
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# testnet can be lumpy.
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cache_room = self.min_cache_size // self.ave_size
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count = min(daemon_height - self.fetched_height, cache_room)
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count = min(500, max(count, 0))
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if not count:
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self.caught_up = True
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return False
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first = self.fetched_height + 1
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hex_hashes = await daemon.block_hex_hashes(first, count)
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if self.caught_up:
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self.logger.info('new block height {:,d} hash {}'
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.format(first + count-1, hex_hashes[-1]))
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blocks = await daemon.raw_blocks(hex_hashes)
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assert count == len(blocks)
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# Special handling for genesis block
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if first == 0:
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blocks[0] = self.coin.genesis_block(blocks[0])
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self.logger.info(f'verified genesis block with hash {hex_hashes[0]}')
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# Update our recent average block size estimate
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size = sum(len(block) for block in blocks)
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if count >= 10:
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self.ave_size = size // count
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else:
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self.ave_size = (size + (10 - count) * self.ave_size) // 10
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self.blocks.extend(blocks)
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self.cache_size += size
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self.fetched_height += count
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self.blocks_event.set()
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self.refill_event.clear()
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return True
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