poky/bitbake/lib/hashserv/server.py - mdmillerii/openbmc - Gitiles

 # Copyright (C) 2019 Garmin Ltd.
 #
 # SPDX-License-Identifier: GPL-2.0-only
 #

 from contextlib import closing, contextmanager
 from datetime import datetime
 import asyncio
 import logging
 import math
 import time
 from . import create_async_client, TABLE_COLUMNS
 import bb.asyncrpc


 logger = logging.getLogger('hashserv.server')


 class Measurement(object):
     def __init__(self, sample):
         self.sample = sample

     def start(self):
         self.start_time = time.perf_counter()

     def end(self):
         self.sample.add(time.perf_counter() - self.start_time)

     def __enter__(self):
         self.start()
         return self

     def __exit__(self, *args, **kwargs):
         self.end()


 class Sample(object):
     def __init__(self, stats):
         self.stats = stats
         self.num_samples = 0
         self.elapsed = 0

     def measure(self):
         return Measurement(self)

     def __enter__(self):
         return self

     def __exit__(self, *args, **kwargs):
         self.end()

     def add(self, elapsed):
         self.num_samples += 1
         self.elapsed += elapsed

     def end(self):
         if self.num_samples:
             self.stats.add(self.elapsed)
             self.num_samples = 0
             self.elapsed = 0


 class Stats(object):
     def __init__(self):
         self.reset()

     def reset(self):
         self.num = 0
         self.total_time = 0
         self.max_time = 0
         self.m = 0
         self.s = 0
         self.current_elapsed = None

     def add(self, elapsed):
         self.num += 1
         if self.num == 1:
             self.m = elapsed
             self.s = 0
         else:
             last_m = self.m
             self.m = last_m + (elapsed - last_m) / self.num
             self.s = self.s + (elapsed - last_m) * (elapsed - self.m)

         self.total_time += elapsed

         if self.max_time < elapsed:
             self.max_time = elapsed

     def start_sample(self):
         return Sample(self)

     @property
     def average(self):
         if self.num == 0:
             return 0
         return self.total_time / self.num

     @property
     def stdev(self):
         if self.num <= 1:
             return 0
         return math.sqrt(self.s / (self.num - 1))

     def todict(self):
         return {k: getattr(self, k) for k in ('num', 'total_time', 'max_time', 'average', 'stdev')}


 def insert_task(cursor, data, ignore=False):
     keys = sorted(data.keys())
     query = '''INSERT%s INTO tasks_v2 (%s) VALUES (%s)''' % (
         " OR IGNORE" if ignore else "",
         ', '.join(keys),
         ', '.join(':' + k for k in keys))
     cursor.execute(query, data)

 async def copy_from_upstream(client, db, method, taskhash):
     d = await client.get_taskhash(method, taskhash, True)
     if d is not None:
         # Filter out unknown columns
         d = {k: v for k, v in d.items() if k in TABLE_COLUMNS}

         with closing(db.cursor()) as cursor:
             insert_task(cursor, d)
             db.commit()

     return d

 async def copy_outhash_from_upstream(client, db, method, outhash, taskhash):
     d = await client.get_outhash(method, outhash, taskhash)
     if d is not None:
         # Filter out unknown columns
         d = {k: v for k, v in d.items() if k in TABLE_COLUMNS}

         with closing(db.cursor()) as cursor:
             insert_task(cursor, d)
             db.commit()

     return d

 class ServerClient(bb.asyncrpc.AsyncServerConnection):
     FAST_QUERY = 'SELECT taskhash, method, unihash FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
     ALL_QUERY =  'SELECT *                         FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
     OUTHASH_QUERY = '''
         -- Find tasks with a matching outhash (that is, tasks that
         -- are equivalent)
         SELECT * FROM tasks_v2 WHERE method=:method AND outhash=:outhash

         -- If there is an exact match on the taskhash, return it.
         -- Otherwise return the oldest matching outhash of any
         -- taskhash
         ORDER BY CASE WHEN taskhash=:taskhash THEN 1 ELSE 2 END,
             created ASC

         -- Only return one row
         LIMIT 1
         '''

     def __init__(self, reader, writer, db, request_stats, backfill_queue, upstream, read_only):
         super().__init__(reader, writer, 'OEHASHEQUIV', logger)
         self.db = db
         self.request_stats = request_stats
         self.max_chunk = bb.asyncrpc.DEFAULT_MAX_CHUNK
         self.backfill_queue = backfill_queue
         self.upstream = upstream

         self.handlers.update({
             'get': self.handle_get,
             'get-outhash': self.handle_get_outhash,
             'get-stream': self.handle_get_stream,
             'get-stats': self.handle_get_stats,
         })

         if not read_only:
             self.handlers.update({
                 'report': self.handle_report,
                 'report-equiv': self.handle_equivreport,
                 'reset-stats': self.handle_reset_stats,
                 'backfill-wait': self.handle_backfill_wait,
             })

     def validate_proto_version(self):
         return (self.proto_version > (1, 0) and self.proto_version <= (1, 1))

     async def process_requests(self):
         if self.upstream is not None:
             self.upstream_client = await create_async_client(self.upstream)
         else:
             self.upstream_client = None

         await super().process_requests()

         if self.upstream_client is not None:
             await self.upstream_client.close()

     async def dispatch_message(self, msg):
         for k in self.handlers.keys():
             if k in msg:
                 logger.debug('Handling %s' % k)
                 if 'stream' in k:
                     await self.handlers[k](msg[k])
                 else:
                     with self.request_stats.start_sample() as self.request_sample, \
                             self.request_sample.measure():
                         await self.handlers[k](msg[k])
                 return

         raise bb.asyncrpc.ClientError("Unrecognized command %r" % msg)

     async def handle_get(self, request):
         method = request['method']
         taskhash = request['taskhash']

         if request.get('all', False):
             row = self.query_equivalent(method, taskhash, self.ALL_QUERY)
         else:
             row = self.query_equivalent(method, taskhash, self.FAST_QUERY)

         if row is not None:
             logger.debug('Found equivalent task %s -> %s', (row['taskhash'], row['unihash']))
             d = {k: row[k] for k in row.keys()}
         elif self.upstream_client is not None:
             d = await copy_from_upstream(self.upstream_client, self.db, method, taskhash)
         else:
             d = None

         self.write_message(d)

     async def handle_get_outhash(self, request):
         with closing(self.db.cursor()) as cursor:
             cursor.execute(self.OUTHASH_QUERY,
                            {k: request[k] for k in ('method', 'outhash', 'taskhash')})

             row = cursor.fetchone()

         if row is not None:
             logger.debug('Found equivalent outhash %s -> %s', (row['outhash'], row['unihash']))
             d = {k: row[k] for k in row.keys()}
         else:
             d = None

         self.write_message(d)

     async def handle_get_stream(self, request):
         self.write_message('ok')

         while True:
             upstream = None

             l = await self.reader.readline()
             if not l:
                 return

             try:
                 # This inner loop is very sensitive and must be as fast as
                 # possible (which is why the request sample is handled manually
                 # instead of using 'with', and also why logging statements are
                 # commented out.
                 self.request_sample = self.request_stats.start_sample()
                 request_measure = self.request_sample.measure()
                 request_measure.start()

                 l = l.decode('utf-8').rstrip()
                 if l == 'END':
                     self.writer.write('ok\n'.encode('utf-8'))
                     return

                 (method, taskhash) = l.split()
                 #logger.debug('Looking up %s %s' % (method, taskhash))
                 row = self.query_equivalent(method, taskhash, self.FAST_QUERY)
                 if row is not None:
                     msg = ('%s\n' % row['unihash']).encode('utf-8')
                     #logger.debug('Found equivalent task %s -> %s', (row['taskhash'], row['unihash']))
                 elif self.upstream_client is not None:
                     upstream = await self.upstream_client.get_unihash(method, taskhash)
                     if upstream:
                         msg = ("%s\n" % upstream).encode("utf-8")
                     else:
                         msg = "\n".encode("utf-8")
                 else:
                     msg = '\n'.encode('utf-8')

                 self.writer.write(msg)
             finally:
                 request_measure.end()
                 self.request_sample.end()

             await self.writer.drain()

             # Post to the backfill queue after writing the result to minimize
             # the turn around time on a request
             if upstream is not None:
                 await self.backfill_queue.put((method, taskhash))

     async def handle_report(self, data):
         with closing(self.db.cursor()) as cursor:
             cursor.execute(self.OUTHASH_QUERY,
                            {k: data[k] for k in ('method', 'outhash', 'taskhash')})

             row = cursor.fetchone()

             if row is None and self.upstream_client:
                 # Try upstream
                 row = await copy_outhash_from_upstream(self.upstream_client,
                                                        self.db,
                                                        data['method'],
                                                        data['outhash'],
                                                        data['taskhash'])

             # If no matching outhash was found, or one *was* found but it
             # wasn't an exact match on the taskhash, a new entry for this
             # taskhash should be added
             if row is None or row['taskhash'] != data['taskhash']:
                 # If a row matching the outhash was found, the unihash for
                 # the new taskhash should be the same as that one.
                 # Otherwise the caller provided unihash is used.
                 unihash = data['unihash']
                 if row is not None:
                     unihash = row['unihash']

                 insert_data = {
                     'method': data['method'],
                     'outhash': data['outhash'],
                     'taskhash': data['taskhash'],
                     'unihash': unihash,
                     'created': datetime.now()
                 }

                 for k in ('owner', 'PN', 'PV', 'PR', 'task', 'outhash_siginfo'):
                     if k in data:
                         insert_data[k] = data[k]

                 insert_task(cursor, insert_data)
                 self.db.commit()

                 logger.info('Adding taskhash %s with unihash %s',
                             data['taskhash'], unihash)

                 d = {
                     'taskhash': data['taskhash'],
                     'method': data['method'],
                     'unihash': unihash
                 }
             else:
                 d = {k: row[k] for k in ('taskhash', 'method', 'unihash')}

         self.write_message(d)

     async def handle_equivreport(self, data):
         with closing(self.db.cursor()) as cursor:
             insert_data = {
                 'method': data['method'],
                 'outhash': "",
                 'taskhash': data['taskhash'],
                 'unihash': data['unihash'],
                 'created': datetime.now()
             }

             for k in ('owner', 'PN', 'PV', 'PR', 'task', 'outhash_siginfo'):
                 if k in data:
                     insert_data[k] = data[k]

             insert_task(cursor, insert_data, ignore=True)
             self.db.commit()

             # Fetch the unihash that will be reported for the taskhash. If the
             # unihash matches, it means this row was inserted (or the mapping
             # was already valid)
             row = self.query_equivalent(data['method'], data['taskhash'], self.FAST_QUERY)

             if row['unihash'] == data['unihash']:
                 logger.info('Adding taskhash equivalence for %s with unihash %s',
                                 data['taskhash'], row['unihash'])

             d = {k: row[k] for k in ('taskhash', 'method', 'unihash')}

         self.write_message(d)


     async def handle_get_stats(self, request):
         d = {
             'requests': self.request_stats.todict(),
         }

         self.write_message(d)

     async def handle_reset_stats(self, request):
         d = {
             'requests': self.request_stats.todict(),
         }

         self.request_stats.reset()
         self.write_message(d)

     async def handle_backfill_wait(self, request):
         d = {
             'tasks': self.backfill_queue.qsize(),
         }
         await self.backfill_queue.join()
         self.write_message(d)

     def query_equivalent(self, method, taskhash, query):
         # This is part of the inner loop and must be as fast as possible
         try:
             cursor = self.db.cursor()
             cursor.execute(query, {'method': method, 'taskhash': taskhash})
             return cursor.fetchone()
         except:
             cursor.close()


 class Server(bb.asyncrpc.AsyncServer):
     def __init__(self, db, loop=None, upstream=None, read_only=False):
         if upstream and read_only:
             raise bb.asyncrpc.ServerError("Read-only hashserv cannot pull from an upstream server")

         super().__init__(logger, loop)

         self.request_stats = Stats()
         self.db = db
         self.upstream = upstream
         self.read_only = read_only

     def accept_client(self, reader, writer):
         return ServerClient(reader, writer, self.db, self.request_stats, self.backfill_queue, self.upstream, self.read_only)

     @contextmanager
     def _backfill_worker(self):
         async def backfill_worker_task():
             client = await create_async_client(self.upstream)
             try:
                 while True:
                     item = await self.backfill_queue.get()
                     if item is None:
                         self.backfill_queue.task_done()
                         break
                     method, taskhash = item
                     await copy_from_upstream(client, self.db, method, taskhash)
                     self.backfill_queue.task_done()
             finally:
                 await client.close()

         async def join_worker(worker):
             await self.backfill_queue.put(None)
             await worker

         if self.upstream is not None:
             worker = asyncio.ensure_future(backfill_worker_task())
             try:
                 yield
             finally:
                 self.loop.run_until_complete(join_worker(worker))
         else:
             yield

     def run_loop_forever(self):
         self.backfill_queue = asyncio.Queue()

         with self._backfill_worker():
             super().run_loop_forever()
	# Copyright (C) 2019 Garmin Ltd.
	#
	# SPDX-License-Identifier: GPL-2.0-only
	#

	from contextlib import closing, contextmanager
	from datetime import datetime
	import asyncio
	import logging
	import math
	import time
	from . import create_async_client, TABLE_COLUMNS
	import bb.asyncrpc


	logger = logging.getLogger('hashserv.server')


	class Measurement(object):
	def __init__(self, sample):
	self.sample = sample

	def start(self):
	self.start_time = time.perf_counter()

	def end(self):
	self.sample.add(time.perf_counter() - self.start_time)

	def __enter__(self):
	self.start()
	return self

	def __exit__(self, args, *kwargs):
	self.end()


	class Sample(object):
	def __init__(self, stats):
	self.stats = stats
	self.num_samples = 0
	self.elapsed = 0

	def measure(self):
	return Measurement(self)

	def __enter__(self):
	return self

	def __exit__(self, args, *kwargs):
	self.end()

	def add(self, elapsed):
	self.num_samples += 1
	self.elapsed += elapsed

	def end(self):
	if self.num_samples:
	self.stats.add(self.elapsed)
	self.num_samples = 0
	self.elapsed = 0


	class Stats(object):
	def __init__(self):
	self.reset()

	def reset(self):
	self.num = 0
	self.total_time = 0
	self.max_time = 0
	self.m = 0
	self.s = 0
	self.current_elapsed = None

	def add(self, elapsed):
	self.num += 1
	if self.num == 1:
	self.m = elapsed
	self.s = 0
	else:
	last_m = self.m
	self.m = last_m + (elapsed - last_m) / self.num
	self.s = self.s + (elapsed - last_m) * (elapsed - self.m)

	self.total_time += elapsed

	if self.max_time < elapsed:
	self.max_time = elapsed

	def start_sample(self):
	return Sample(self)

	@property
	def average(self):
	if self.num == 0:
	return 0
	return self.total_time / self.num

	@property
	def stdev(self):
	if self.num <= 1:
	return 0
	return math.sqrt(self.s / (self.num - 1))

	def todict(self):
	return {k: getattr(self, k) for k in ('num', 'total_time', 'max_time', 'average', 'stdev')}


	def insert_task(cursor, data, ignore=False):
	keys = sorted(data.keys())
	query = '''INSERT%s INTO tasks_v2 (%s) VALUES (%s)''' % (
	" OR IGNORE" if ignore else "",
	', '.join(keys),
	', '.join(':' + k for k in keys))
	cursor.execute(query, data)

	async def copy_from_upstream(client, db, method, taskhash):
	d = await client.get_taskhash(method, taskhash, True)
	if d is not None:
	# Filter out unknown columns
	d = {k: v for k, v in d.items() if k in TABLE_COLUMNS}

	with closing(db.cursor()) as cursor:
	insert_task(cursor, d)
	db.commit()

	return d

	async def copy_outhash_from_upstream(client, db, method, outhash, taskhash):
	d = await client.get_outhash(method, outhash, taskhash)
	if d is not None:
	# Filter out unknown columns
	d = {k: v for k, v in d.items() if k in TABLE_COLUMNS}

	with closing(db.cursor()) as cursor:
	insert_task(cursor, d)
	db.commit()

	return d

	class ServerClient(bb.asyncrpc.AsyncServerConnection):
	FAST_QUERY = 'SELECT taskhash, method, unihash FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
	ALL_QUERY = 'SELECT * FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
	OUTHASH_QUERY = '''
	-- Find tasks with a matching outhash (that is, tasks that
	-- are equivalent)
	SELECT * FROM tasks_v2 WHERE method=:method AND outhash=:outhash

	-- If there is an exact match on the taskhash, return it.
	-- Otherwise return the oldest matching outhash of any
	-- taskhash
	ORDER BY CASE WHEN taskhash=:taskhash THEN 1 ELSE 2 END,
	created ASC

	-- Only return one row
	LIMIT 1
	'''

	def __init__(self, reader, writer, db, request_stats, backfill_queue, upstream, read_only):
	super().__init__(reader, writer, 'OEHASHEQUIV', logger)
	self.db = db
	self.request_stats = request_stats
	self.max_chunk = bb.asyncrpc.DEFAULT_MAX_CHUNK
	self.backfill_queue = backfill_queue
	self.upstream = upstream

	self.handlers.update({
	'get': self.handle_get,
	'get-outhash': self.handle_get_outhash,
	'get-stream': self.handle_get_stream,
	'get-stats': self.handle_get_stats,
	})

	if not read_only:
	self.handlers.update({
	'report': self.handle_report,
	'report-equiv': self.handle_equivreport,
	'reset-stats': self.handle_reset_stats,
	'backfill-wait': self.handle_backfill_wait,
	})

	def validate_proto_version(self):
	return (self.proto_version > (1, 0) and self.proto_version <= (1, 1))

	async def process_requests(self):
	if self.upstream is not None:
	self.upstream_client = await create_async_client(self.upstream)
	else:
	self.upstream_client = None

	await super().process_requests()

	if self.upstream_client is not None:
	await self.upstream_client.close()

	async def dispatch_message(self, msg):
	for k in self.handlers.keys():
	if k in msg:
	logger.debug('Handling %s' % k)
	if 'stream' in k:
	await self.handlers[k](msg[k])
	else:
	with self.request_stats.start_sample() as self.request_sample, \
	self.request_sample.measure():
	await self.handlers[k](msg[k])
	return

	raise bb.asyncrpc.ClientError("Unrecognized command %r" % msg)

	async def handle_get(self, request):
	method = request['method']
	taskhash = request['taskhash']

	if request.get('all', False):
	row = self.query_equivalent(method, taskhash, self.ALL_QUERY)
	else:
	row = self.query_equivalent(method, taskhash, self.FAST_QUERY)

	if row is not None:
	logger.debug('Found equivalent task %s -> %s', (row['taskhash'], row['unihash']))
	d = {k: row[k] for k in row.keys()}
	elif self.upstream_client is not None:
	d = await copy_from_upstream(self.upstream_client, self.db, method, taskhash)
	else:
	d = None

	self.write_message(d)

	async def handle_get_outhash(self, request):
	with closing(self.db.cursor()) as cursor:
	cursor.execute(self.OUTHASH_QUERY,
	{k: request[k] for k in ('method', 'outhash', 'taskhash')})

	row = cursor.fetchone()

	if row is not None:
	logger.debug('Found equivalent outhash %s -> %s', (row['outhash'], row['unihash']))
	d = {k: row[k] for k in row.keys()}
	else:
	d = None

	self.write_message(d)

	async def handle_get_stream(self, request):
	self.write_message('ok')

	while True:
	upstream = None

	l = await self.reader.readline()
	if not l:
	return

	try:
	# This inner loop is very sensitive and must be as fast as
	# possible (which is why the request sample is handled manually
	# instead of using 'with', and also why logging statements are
	# commented out.
	self.request_sample = self.request_stats.start_sample()
	request_measure = self.request_sample.measure()
	request_measure.start()

	l = l.decode('utf-8').rstrip()
	if l == 'END':
	self.writer.write('ok\n'.encode('utf-8'))
	return

	(method, taskhash) = l.split()
	#logger.debug('Looking up %s %s' % (method, taskhash))
	row = self.query_equivalent(method, taskhash, self.FAST_QUERY)
	if row is not None:
	msg = ('%s\n' % row['unihash']).encode('utf-8')
	#logger.debug('Found equivalent task %s -> %s', (row['taskhash'], row['unihash']))
	elif self.upstream_client is not None:
	upstream = await self.upstream_client.get_unihash(method, taskhash)
	if upstream:
	msg = ("%s\n" % upstream).encode("utf-8")
	else:
	msg = "\n".encode("utf-8")
	else:
	msg = '\n'.encode('utf-8')

	self.writer.write(msg)
	finally:
	request_measure.end()
	self.request_sample.end()

	await self.writer.drain()

	# Post to the backfill queue after writing the result to minimize
	# the turn around time on a request
	if upstream is not None:
	await self.backfill_queue.put((method, taskhash))

	async def handle_report(self, data):
	with closing(self.db.cursor()) as cursor:
	cursor.execute(self.OUTHASH_QUERY,
	{k: data[k] for k in ('method', 'outhash', 'taskhash')})

	row = cursor.fetchone()

	if row is None and self.upstream_client:
	# Try upstream
	row = await copy_outhash_from_upstream(self.upstream_client,
	self.db,
	data['method'],
	data['outhash'],
	data['taskhash'])

	# If no matching outhash was found, or one was found but it
	# wasn't an exact match on the taskhash, a new entry for this
	# taskhash should be added
	if row is None or row['taskhash'] != data['taskhash']:
	# If a row matching the outhash was found, the unihash for
	# the new taskhash should be the same as that one.
	# Otherwise the caller provided unihash is used.
	unihash = data['unihash']
	if row is not None:
	unihash = row['unihash']

	insert_data = {
	'method': data['method'],
	'outhash': data['outhash'],
	'taskhash': data['taskhash'],
	'unihash': unihash,
	'created': datetime.now()
	}

	for k in ('owner', 'PN', 'PV', 'PR', 'task', 'outhash_siginfo'):
	if k in data:
	insert_data[k] = data[k]

	insert_task(cursor, insert_data)
	self.db.commit()

	logger.info('Adding taskhash %s with unihash %s',
	data['taskhash'], unihash)

	d = {
	'taskhash': data['taskhash'],
	'method': data['method'],
	'unihash': unihash
	}
	else:
	d = {k: row[k] for k in ('taskhash', 'method', 'unihash')}

	self.write_message(d)

	async def handle_equivreport(self, data):
	with closing(self.db.cursor()) as cursor:
	insert_data = {
	'method': data['method'],
	'outhash': "",
	'taskhash': data['taskhash'],
	'unihash': data['unihash'],
	'created': datetime.now()
	}

	for k in ('owner', 'PN', 'PV', 'PR', 'task', 'outhash_siginfo'):
	if k in data:
	insert_data[k] = data[k]

	insert_task(cursor, insert_data, ignore=True)
	self.db.commit()

	# Fetch the unihash that will be reported for the taskhash. If the
	# unihash matches, it means this row was inserted (or the mapping
	# was already valid)
	row = self.query_equivalent(data['method'], data['taskhash'], self.FAST_QUERY)

	if row['unihash'] == data['unihash']:
	logger.info('Adding taskhash equivalence for %s with unihash %s',
	data['taskhash'], row['unihash'])

	d = {k: row[k] for k in ('taskhash', 'method', 'unihash')}

	self.write_message(d)


	async def handle_get_stats(self, request):
	d = {
	'requests': self.request_stats.todict(),
	}

	self.write_message(d)

	async def handle_reset_stats(self, request):
	d = {
	'requests': self.request_stats.todict(),
	}

	self.request_stats.reset()
	self.write_message(d)

	async def handle_backfill_wait(self, request):
	d = {
	'tasks': self.backfill_queue.qsize(),
	}
	await self.backfill_queue.join()
	self.write_message(d)

	def query_equivalent(self, method, taskhash, query):
	# This is part of the inner loop and must be as fast as possible
	try:
	cursor = self.db.cursor()
	cursor.execute(query, {'method': method, 'taskhash': taskhash})
	return cursor.fetchone()
	except:
	cursor.close()


	class Server(bb.asyncrpc.AsyncServer):
	def __init__(self, db, loop=None, upstream=None, read_only=False):
	if upstream and read_only:
	raise bb.asyncrpc.ServerError("Read-only hashserv cannot pull from an upstream server")

	super().__init__(logger, loop)

	self.request_stats = Stats()
	self.db = db
	self.upstream = upstream
	self.read_only = read_only

	def accept_client(self, reader, writer):
	return ServerClient(reader, writer, self.db, self.request_stats, self.backfill_queue, self.upstream, self.read_only)

	@contextmanager
	def _backfill_worker(self):
	async def backfill_worker_task():
	client = await create_async_client(self.upstream)
	try:
	while True:
	item = await self.backfill_queue.get()
	if item is None:
	self.backfill_queue.task_done()
	break
	method, taskhash = item
	await copy_from_upstream(client, self.db, method, taskhash)
	self.backfill_queue.task_done()
	finally:
	await client.close()

	async def join_worker(worker):
	await self.backfill_queue.put(None)
	await worker

	if self.upstream is not None:
	worker = asyncio.ensure_future(backfill_worker_task())
	try:
	yield
	finally:
	self.loop.run_until_complete(join_worker(worker))
	else:
	yield

	def run_loop_forever(self):
	self.backfill_queue = asyncio.Queue()

	with self._backfill_worker():
	super().run_loop_forever()