X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/dc08f17cc3c90714efafb11e38e27ca8ea1b5f5b..ba34a22d9918ae97306472c04701e69090821c82:/sdk/python/arvados/diskcache.py

diff --git a/sdk/python/arvados/diskcache.py b/sdk/python/arvados/diskcache.py
new file mode 100644
index 0000000000..15afa23a8d
--- /dev/null
+++ b/sdk/python/arvados/diskcache.py
@@ -0,0 +1,238 @@
+# 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