class BufferBlock(object):
+'''
+A BufferBlock is a stand-in for a Keep block that is in the process of being
+written. Writers can append to it, get the size, and compute the Keep locator.
+
+There are three valid states:
+
+WRITABLE - can append
+
+PENDING - is in the process of being uploaded to Keep, append is an error
+
+COMMITTED - the block has been written to Keep, its internal buffer has been
+released, and the BufferBlock should be discarded in favor of fetching the
+block through normal Keep means.
+'''
WRITABLE = 0
PENDING = 1
COMMITTED = 2
- def __init__(self, blockid, starting_size):
+ def __init__(self, blockid, starting_capacity):
+ '''
+ blockid: the identifier for this block
+ starting_capacity: the initial buffer capacity
+ '''
self.blockid = blockid
- self.buffer_block = bytearray(starting_size)
+ self.buffer_block = bytearray(starting_capacity)
self.buffer_view = memoryview(self.buffer_block)
self.write_pointer = 0
self.state = BufferBlock.WRITABLE
self._locator = None
def append(self, data):
+ '''
+ Append some data to the buffer. Only valid if the block is in WRITABLE
+ state. Implements an expanding buffer, doubling capacity as needed to
+ accomdate all the data.
+ '''
if self.state == BufferBlock.WRITABLE:
while (self.write_pointer+len(data)) > len(self.buffer_block):
new_buffer_block = bytearray(len(self.buffer_block) * 2)
raise AssertionError("Buffer block is not writable")
def size(self):
+ '''Amount of data written to the buffer'''
return self.write_pointer
def locator(self):
+ '''The Keep locator for this buffer's contents.'''
if self._locator is None:
self._locator = "%s+%i" % (hashlib.md5(self.buffer_view[0:self.write_pointer]).hexdigest(), self.size())
return self._locator
class AsyncKeepWriteErrors(Exception):
+ '''
+ Roll up one or more Keep write exceptions (generated by background
+ threads) into a single one.
+ '''
def __init__(self, errors):
self.errors = errors
return "\n".join(self.errors)
class BlockManager(object):
+ '''
+ BlockManager handles buffer blocks, background block uploads, and
+ background block prefetch for a Collection of ArvadosFiles.
+ '''
def __init__(self, keep):
+ '''keep: KeepClient object to use'''
self._keep = keep
self._bufferblocks = {}
self._put_queue = None
self._prefetch_queue = None
self._prefetch_threads = None
- def alloc_bufferblock(self, blockid=None, starting_size=2**14):
+ def alloc_bufferblock(self, blockid=None, starting_capacity=2**14):
+ '''
+ Allocate a new, empty bufferblock in WRITABLE state and return it.
+ blockid: optional block identifier, otherwise one will be automatically assigned
+ starting_capacity: optional capacity, otherwise will use default capacity
+ '''
if blockid is None:
blockid = "bufferblock%i" % len(self._bufferblocks)
- bb = BufferBlock(blockid, starting_size=starting_size)
+ bb = BufferBlock(blockid, starting_capacity=starting_capacity)
self._bufferblocks[bb.blockid] = bb
return bb
def stop_threads(self):
+ '''
+ Shut down and wait for background upload and download threads to finish.
+ '''
if self._put_threads is not None:
for t in self._put_threads:
self._put_queue.put(None)
self._prefetch_queue = None
def commit_bufferblock(self, block):
+ '''
+ Initiate a background upload of a bufferblock. This will block if the
+ upload queue is at capacity, otherwise it will return immediately.
+ '''
+
def worker(self):
+ '''
+ Background uploader thread.
+ '''
while True:
try:
b = self._put_queue.get()
self._put_queue.task_done()
if self._put_threads is None:
+ # Start uploader threads.
+
+ # If we don't limit the Queue size, the upload queue can quickly
+ # grow to take up gigabytes of RAM if the writing process is
+ # generating data more quickly than it can be send to the Keep
+ # servers.
+ #
+ # With two upload threads and a queue size of 2, this means up to 4
+ # blocks pending. If they are full 64 MiB blocks, that means up to
+ # 256 MiB of internal buffering, which is the same size as the
+ # default download block cache in KeepClient.
self._put_queue = Queue.Queue(maxsize=2)
self._put_errors = Queue.Queue()
self._put_threads = [threading.Thread(target=worker, args=(self,)),
t.daemon = True
t.start()
+ # Mark the block as PENDING so to disallow any more appends.
block.state = BufferBlock.PENDING
self._put_queue.put(block)
def get_block(self, locator, num_retries, cache_only=False):
+ '''
+ Fetch a block. First checks to see if the locator is a BufferBlock and
+ return that, if not, passes the request through to KeepClient.get().
+ '''
if locator in self._bufferblocks:
bb = self._bufferblocks[locator]
if bb.state != BufferBlock.COMMITTED:
return self._keep.get(locator, num_retries=num_retries, cache_only=cache_only)
def commit_all(self):
+ '''
+ Commit all outstanding buffer blocks. Unlike commit_bufferblock(), this
+ is a synchronous call, and will not return until all buffer blocks are
+ uploaded. Raises AsyncKeepWriteErrors() if any blocks failed to
+ upload.
+ '''
for k,v in self._bufferblocks.items():
if v.state == BufferBlock.WRITABLE:
self.commit_bufferblock(v)
raise AsyncKeepWriteErrors(e)
def block_prefetch(self, locator):
+ '''
+ Initiate a background download of a block. This assumes that the
+ underlying KeepClient implements a block cache, so repeated requests
+ for the same block will not result in repeated downloads (unless the
+ block is evicted from the cache.) This method does not block.
+ '''
def worker(self):
+ '''Background downloader thread.'''
while True:
try:
b = self._prefetch_queue.get()
self._prefetch_queue.put(locator)
class ArvadosFile(object):
+ '''
+ Manages the underyling representation of a file in Keep as a sequence of
+ segments over a set of blocks, supporting random read/write access.
+ '''
+
def __init__(self, parent, stream=[], segments=[]):
'''
stream: a list of Range objects representing a block stream
for s in segments:
self.add_segment(stream, s.locator, s.range_size)
self._current_bblock = None
+ self.lock = threading.Lock()
+
+ def clone(self):
+ '''
+ Make a copy of this file.
+ '''
+ # TODO: copy bufferblocks.
+ with self.lock:
+ cp = ArvadosFile()
+ cp.parent = self.parent
+ cp._modified = False
+ cp.segments = [Range(r.locator, r.range_start, r.range_size, r.segment_offset) for r in self.segments]
+ return cp
def set_unmodified(self):
self._modified = False
class ArvadosFileReader(ArvadosFileReaderBase):
def __init__(self, arvadosfile, name, mode="r", num_retries=None):
super(ArvadosFileReader, self).__init__(name, mode, num_retries=num_retries)
- self.arvadosfile = arvadosfile
+ self.arvadosfile = arvadosfile.clone()
def size(self):
return self.arvadosfile.size()
def flush(self):
pass
+
+class SynchronizedArvadosFile(object):
+ def __init__(self, arvadosfile):
+ self.arvadosfile = arvadosfile
+
+ def clone(self):
+ return self
+
+ def __getattr__(self, name):
+ with self.arvadosfile.lock:
+ return getattr(self.arvadosfile, name)
+
+
class ArvadosFileWriter(ArvadosFileReader):
def __init__(self, arvadosfile, name, mode, num_retries=None):
- super(ArvadosFileWriter, self).__init__(arvadosfile, name, mode, num_retries=num_retries)
+ self.arvadosfile = SynchronizedArvadosFile(arvadosfile)
+ super(ArvadosFileWriter, self).__init__(self.arvadosfile, name, mode, num_retries=num_retries)
@ArvadosFileBase._before_close
@retry_method
projects / arvados.git / blobdiff