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objectstore: use a context also for Object.write

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Reading from an `Object` via `read` already uses a context manager
to manage the read-only bind mount and also maintain a count of
currently active readers. With this an attempt to start a new
`write` operation while readers were active can be detected and
an exception is throw. Since `write` was not introducing a context
the inverted situation, i.e. reads while a write is ongoing, was
not possible to detect.
This commit therefore introduces a context also for `.write` so
that we can enforce the policy to have either many readers but no
writers, or just one writer and no readers.
A bind mount is also used for write (in read-write mode) to hide
the internal path of the tree.
This commit is contained in:
Christian Kellner 2020-02-26 10:35:58 +01:00 • committed by Tom Gundersen
parent 2266d3fada
commit 4b790ac284
3 changed files with 104 additions and 60 deletions
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102
test/test_objectstore.py
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@ -29,9 +29,9 @@ class TestObjectStore(unittest.TestCase):
assert len(os.listdir(object_store.objects)) == 0
with object_store.new() as tree:
path = tree.write()
p = Path(f"{path}/A")
p.touch()
with tree.write() as path:
p = Path(f"{path}/A")
p.touch()
object_store.commit(tree, "a")
assert object_store.contains("a")
@ -42,11 +42,11 @@ class TestObjectStore(unittest.TestCase):
assert len(os.listdir(f"{object_store.refs}/a/")) == 1
with object_store.new() as tree:
path = tree.write()
p = Path(f"{path}/A")
p.touch()
p = Path(f"{path}/B")
p.touch()
with tree.write() as path:
p = Path(f"{path}/A")
p.touch()
p = Path(f"{path}/B")
p.touch()
object_store.commit(tree, "b")
assert object_store.contains("b")
@ -65,15 +65,15 @@ class TestObjectStore(unittest.TestCase):
with tempfile.TemporaryDirectory(dir="/var/tmp") as tmp:
object_store = objectstore.ObjectStore(tmp)
with object_store.new() as tree:
path = tree.write()
p = Path(f"{path}/A")
p.touch()
with tree.write() as path:
p = Path(f"{path}/A")
p.touch()
object_store.commit(tree, "a")
with object_store.new() as tree:
path = tree.write()
shutil.copy2(f"{object_store.refs}/a/A",
f"{path}/A")
with tree.write() as path:
shutil.copy2(f"{object_store.refs}/a/A",
f"{path}/A")
object_store.commit(tree, "b")
assert os.path.exists(f"{object_store.refs}/a")
@ -90,9 +90,9 @@ class TestObjectStore(unittest.TestCase):
with tempfile.TemporaryDirectory(dir="/var/tmp") as tmp:
object_store = objectstore.ObjectStore(tmp)
with object_store.new() as tree:
path = tree.write()
p = Path(f"{path}/A")
p.touch()
with tree.write() as path:
p = Path(f"{path}/A")
p.touch()
object_store.commit(tree, "a")
with object_store.new() as tree:
@ -101,9 +101,9 @@ class TestObjectStore(unittest.TestCase):
with object_store.new() as tree:
tree.base = "b"
path = tree.write()
p = Path(f"{path}/C")
p.touch()
with tree.write() as path:
p = Path(f"{path}/C")
p.touch()
object_store.commit(tree, "c")
assert os.path.exists(f"{object_store.refs}/a/A")
@ -125,7 +125,8 @@ class TestObjectStore(unittest.TestCase):
with object_store.new() as tree:
path = tree.write()
with open(f"{path}/data", "w") as f:
with tree.write() as path, \
open(f"{path}/data", "w") as f:
f.write(data)
st = os.fstat(f.fileno())
data_inode = st.st_ino
@ -159,14 +160,14 @@ class TestObjectStore(unittest.TestCase):
self.assertEqual(st.st_ino, data_inode)
data_read = f.read()
self.assertEqual(data, data_read)
path = tree.write()
# "data" must of course still be present
assert os.path.exists(f"{path}/data")
# but since it is a copy, have a different inode
st = os.stat(f"{path}/data")
self.assertNotEqual(st.st_ino, data_inode)
p = Path(f"{path}/other_data")
p.touch()
with tree.write() as path:
# "data" must of course still be present
assert os.path.exists(f"{path}/data")
# but since it is a copy, have a different inode
st = os.stat(f"{path}/data")
self.assertNotEqual(st.st_ino, data_inode)
p = Path(f"{path}/other_data")
p.touch()
# now that we have written, the treesum
# should have changed
self.assertNotEqual(tree.treesum, x_hash)
@ -178,7 +179,8 @@ class TestObjectStore(unittest.TestCase):
# currently being read from fails
with tree.read() as _:
with self.assertRaises(ValueError):
tree.write()
with tree.write() as _:
pass
# check multiple readers are ok
with tree.read() as _:
@ -188,34 +190,54 @@ class TestObjectStore(unittest.TestCase):
# writing should still fail
with self.assertRaises(ValueError):
tree.write()
with tree.write() as _:
pass
# Now that all readers are gone, writing should
# work
tree.write()
with tree.write() as _:
pass
# and back to reading, one last time
with tree.read() as _:
with self.assertRaises(ValueError):
tree.write()
with tree.write() as _:
pass
# Only one single writer
with tree.write() as _:
# no other readers
with self.assertRaises(ValueError):
with tree.read() as _:
pass
# or other writers
with self.assertRaises(ValueError):
with tree.write() as _:
pass
# one more time
with tree.write() as _:
pass
# tree has exited the context, it should NOT be
# writable anymore
with self.assertRaises(ValueError):
tree.write()
with tree.write() as _:
pass
def test_snapshot(self):
object_store = objectstore.ObjectStore(self.store)
with object_store.new() as tree:
path = tree.write()
p = Path(f"{path}/A")
p.touch()
with tree.write() as path:
p = Path(f"{path}/A")
p.touch()
assert not object_store.contains("a")
object_store.commit(tree, "a")
assert object_store.contains("a")
path = tree.write()
p = Path(f"{path}/B")
p.touch()
with tree.write() as path:
p = Path(f"{path}/B")
p.touch()
object_store.commit(tree, "b")
# check the references exist