inotify: server: new data structure to keep track of changes....
inotify: server: new data structure to keep track of changes.
== Rationale for the new structure ==
Current structure was a dictionary tree. One directory was tracked
as a dictionary:
- keys: file/subdir name
- values:
- for a file, the status (a/r/m/...)
- for a subdir, the directory representing the subdir
It allowed efficient lookups, no matter of the type of the terminal leaf:
for part in path.split('/'): tree = tree[part]
However, there is no way to represent a directory and a file with the same name
because keys are conflicting in the dictionary. Concrete example:
Initial state:
root dir
|- foo (file)
|- bar (file)
# data state is: {'foo': 'n', 'bar': 'n'}
Remove foo:
root dir
|- bar (file)
# Data becomes {'foo': 'r'} until next commit.
Add foo, as a directory, and foo/barbar file:
root dir
|- bar (file)
|-> foo (dir)
|- barbar (file)
# New state should be represented as:
{'foo': {'barbar': 'a'}, 'bar': 'n'}
however, the key "foo" is already used and represents the old file.
The dirstate:
D foo
A foo/barbar
cannot be represented, hence the need for a new structure.
== The new structure ==
'directory' class. Represents one directory level.
* Notable attributes:
Two dictionaries:
- 'files' Maps filename -> status for the current dir.
- 'dirs' Maps subdir's name -> directory object representing the subdir
* methods
- walk(), formerly server.walk
- lookup(), old server.lookup
- dir(), old server.dir
This new class allows embedding all the tree walks/lookups in its own class,
instead of having everything mixed together in server.
Incidently, since files and directories are not stored in the same
dictionaries, we are solving the previous key conflict problem.
The small drawback is that lookup operation is a bit more complex:
for a path a/b/c/d/e we have to check twice the leaf, if e is a directory or a
file.
