--- /dev/null
+# Copyright (C) The Arvados Authors. All rights reserved.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import threading
+import mmap
+import os
+import traceback
+import stat
+import tempfile
+import fcntl
+import time
+import errno
+import logging
+
+_logger = logging.getLogger('arvados.keep')
+
+cacheblock_suffix = ".keepcacheblock"
+
+class DiskCacheSlot(object):
+ __slots__ = ("locator", "ready", "content", "cachedir", "filehandle")
+
+ def __init__(self, locator, cachedir):
+ self.locator = locator
+ self.ready = threading.Event()
+ self.content = None
+ self.cachedir = cachedir
+ self.filehandle = None
+
+ def get(self):
+ self.ready.wait()
+ return self.content
+
+ def set(self, value):
+ tmpfile = None
+ try:
+ if value is None:
+ self.content = None
+ self.ready.set()
+ return
+
+ if len(value) == 0:
+ # Can't mmap a 0 length file
+ self.content = b''
+ self.ready.set()
+ return
+
+ if self.content is not None:
+ # Has been set already
+ self.ready.set()
+ return
+
+ blockdir = os.path.join(self.cachedir, self.locator[0:3])
+ os.makedirs(blockdir, mode=0o700, exist_ok=True)
+
+ final = os.path.join(blockdir, self.locator) + cacheblock_suffix
+
+ self.filehandle = tempfile.NamedTemporaryFile(dir=blockdir, delete=False, prefix="tmp", suffix=cacheblock_suffix)
+ tmpfile = self.filehandle.name
+ os.chmod(tmpfile, stat.S_IRUSR | stat.S_IWUSR)
+
+ # aquire a shared lock, this tells other processes that
+ # we're using this block and to please not delete it.
+ fcntl.flock(self.filehandle, fcntl.LOCK_SH)
+
+ self.filehandle.write(value)
+ self.filehandle.flush()
+ os.rename(tmpfile, final)
+ tmpfile = None
+
+ self.content = mmap.mmap(self.filehandle.fileno(), 0, access=mmap.ACCESS_READ)
+ # only set the event when mmap is successful
+ self.ready.set()
+ finally:
+ if tmpfile is not None:
+ # If the tempfile hasn't been renamed on disk yet, try to delete it.
+ try:
+ os.remove(tmpfile)
+ except:
+ pass
+
+ def size(self):
+ if self.content is None:
+ return 0
+ else:
+ return len(self.content)
+
+ def evict(self):
+ if self.content is not None and len(self.content) > 0:
+ # The mmap region might be in use when we decided to evict
+ # it. This can happen if the cache is too small.
+ #
+ # If we call close() now, it'll throw an error if
+ # something tries to access it.
+ #
+ # However, we don't need to explicitly call mmap.close()
+ #
+ # I confirmed in mmapmodule.c that that both close
+ # and deallocate do the same thing:
+ #
+ # a) close the file descriptor
+ # b) unmap the memory range
+ #
+ # So we can forget it in the cache and delete the file on
+ # disk, and it will tear it down after any other
+ # lingering Python references to the mapped memory are
+ # gone.
+
+ blockdir = os.path.join(self.cachedir, self.locator[0:3])
+ final = os.path.join(blockdir, self.locator) + cacheblock_suffix
+ try:
+ fcntl.flock(self.filehandle, fcntl.LOCK_UN)
+
+ # try to get an exclusive lock, this ensures other
+ # processes are not using the block. It is
+ # nonblocking and will throw an exception if we
+ # can't get it, which is fine because that means
+ # we just won't try to delete it.
+ #
+ # I should note here, the file locking is not
+ # strictly necessary, we could just remove it and
+ # the kernel would ensure that the underlying
+ # inode remains available as long as other
+ # processes still have the file open. However, if
+ # you have multiple processes sharing the cache
+ # and deleting each other's files, you'll end up
+ # with a bunch of ghost files that don't show up
+ # in the file system but are still taking up
+ # space, which isn't particularly user friendly.
+ # The locking strategy ensures that cache blocks
+ # in use remain visible.
+ #
+ fcntl.flock(self.filehandle, fcntl.LOCK_EX | fcntl.LOCK_NB)
+
+ os.remove(final)
+ return True
+ except OSError:
+ pass
+ finally:
+ self.filehandle = None
+ self.content = None
+ return False
+
+ @staticmethod
+ def get_from_disk(locator, cachedir):
+ blockdir = os.path.join(cachedir, locator[0:3])
+ final = os.path.join(blockdir, locator) + cacheblock_suffix
+
+ try:
+ filehandle = open(final, "rb")
+
+ # aquire a shared lock, this tells other processes that
+ # we're using this block and to please not delete it.
+ fcntl.flock(filehandle, fcntl.LOCK_SH)
+
+ content = mmap.mmap(filehandle.fileno(), 0, access=mmap.ACCESS_READ)
+ dc = DiskCacheSlot(locator, cachedir)
+ dc.filehandle = filehandle
+ dc.content = content
+ dc.ready.set()
+ return dc
+ except FileNotFoundError:
+ pass
+ except Exception as e:
+ traceback.print_exc()
+
+ return None
+
+ @staticmethod
+ def cache_usage(cachedir):
+ usage = 0
+ for root, dirs, files in os.walk(cachedir):
+ for name in files:
+ if not name.endswith(cacheblock_suffix):
+ continue
+
+ blockpath = os.path.join(root, name)
+ res = os.stat(blockpath)
+ usage += res.st_size
+ return usage
+
+
+ @staticmethod
+ def init_cache(cachedir, maxslots):
+ #
+ # First check the disk cache works at all by creating a 1 byte cache entry
+ #
+ checkexists = DiskCacheSlot.get_from_disk('0cc175b9c0f1b6a831c399e269772661', cachedir)
+ ds = DiskCacheSlot('0cc175b9c0f1b6a831c399e269772661', cachedir)
+ ds.set(b'a')
+ if checkexists is None:
+ # Don't keep the test entry around unless it existed beforehand.
+ ds.evict()
+
+ # map in all the files in the cache directory, up to max slots.
+ # after max slots, try to delete the excess blocks.
+ #
+ # this gives the calling process ownership of all the blocks
+
+ blocks = []
+ for root, dirs, files in os.walk(cachedir):
+ for name in files:
+ if not name.endswith(cacheblock_suffix):
+ continue
+
+ blockpath = os.path.join(root, name)
+ res = os.stat(blockpath)
+
+ if len(name) == (32+len(cacheblock_suffix)) and not name.startswith("tmp"):
+ blocks.append((name[0:32], res.st_atime))
+ elif name.startswith("tmp") and ((time.time() - res.st_mtime) > 60):
+ # found a temporary file more than 1 minute old,
+ # try to delete it.
+ try:
+ os.remove(blockpath)
+ except:
+ pass
+
+ # sort by access time (atime), going from most recently
+ # accessed (highest timestamp) to least recently accessed
+ # (lowest timestamp).
+ blocks.sort(key=lambda x: x[1], reverse=True)
+
+ # Map in all the files we found, up to maxslots, if we exceed
+ # maxslots, start throwing things out.
+ cachelist = []
+ for b in blocks:
+ got = DiskCacheSlot.get_from_disk(b[0], cachedir)
+ if got is None:
+ continue
+ if len(cachelist) < maxslots:
+ cachelist.append(got)
+ else:
+ # we found more blocks than maxslots, try to
+ # throw it out of the cache.
+ got.evict()
+
+ return cachelist
projects / arvados.git / blobdiff