`StateMgr` got a new `unlock()` method that does what it says on the
tin. We now call it from `bootstrap()` using the new
`util::StateMgrUnlockGuard`, which works in a manner similar to the
`BoolResetter` from `tor_dirmgr`.
(A decent small little task in future might be to unify these types in
some sort of general arti utility crate?)
closes arti#335
This lint is IMO inherently ill-conceived.
I have looked for the reasons why this might be thought to be a good
idea and there were basically two (and they are sort of contradictory):
I. "Calling ‘.clone()` on an Rc, Arc, or Weak can obscure the fact
that only the pointer is being cloned, not the underlying data."
This is the wording from
https://rust-lang.github.io/rust-clippy/v0.0.212/#clone_on_ref_ptr
It is a bit terse; we are left to infer why it is a bad idea to
obscure this fact. It seems to me that if it is bad to obscure some
fact, that must be because the fact is a hazard. But why would it be
a hazard to not copy the underlying data ?
In other languages, faliing to copy the underlying data is a serious
correctness hazard. There is a whose class of bugs where things were
not copied, and then mutated and/or reused in multiple places in ways
that were not what the programmer intended. In my experience, this is
a very common bug when writing Python and Javascript. I'm told it's
common in golang too.
But in Rust this bug is much much harder to write. The data inside an
Arc is immutable. To have this bug you'd have use interior mutability
- ie mess around with Mutex or RefCell. That provides a good barrier
to these kind of accidents.
II. "The reason for writing Rc::clone and Arc::clone [is] to make it
clear that only the pointer is being cloned, as opposed to the
underlying data. The former is always fast, while the latter can
be very expensive depending on what is being cloned."
This is the reasoning found here
https://github.com/rust-lang/rust-clippy/issues/2048
This is saying that *not* using Arc::clone is hazardous.
Specifically, that a deep clone is a performance hazard.
But for this argument, the lint is precisely backwards. It's linting
the "good" case and asking for it to be written in a more explicit
way; while the supposedly bad case can be written conveniently.
Also, many objects (in our codebase, and in all the libraries we use)
that are Clone are in fact simply handles. They contain Arc(s) (or
similar) and are cheap to clone. Indeed, that is the usual case.
It does not make sense to distinguish in the syntax we use to clone
such a handle, whether the handle is a transparent Arc, or an opaque
struct containing one or more other handles.
Forcing Arc::clone to be written as such makes for code churn when a
type is changed from Arc<Something> to Something: Clone, or vice
versa.
To implement this, we had to refactor the tor_circmgr api for
flushing state changes to disk, so that it checks if it has the lock,
and only then tries to store.
Serialisation errors ought not to occur, since they would represent an
attempt to store malformed data, or something. (We always convert to
a string, so the JSON error never contains IO errors or the like.)
Deserialisation errors mean the persistent state is corrupt.
clippy::needless_borrow quibbles here, IMO correctly. Its suggestion
didn't go far enough: output is a String and a &String can be passed
to write as-is for identical effect.
This patch doesn't actually make anything reconfigurable, but it
does create an API that will tell you "you can't change the value of
that!" If the API looks reasonable, I can start making it possible
to change the values of individual items.
Previously it was either all-locked or all-not-locked. Now you can
simulate having the same shared storage opened by multiple managers,
only one of which has the lock.
The Futureproof<T> type lets you serialize and deserialize types whose
representations might change (most useful for enums that might grow
additional variants). It uses #[serde(untagged)] to accomplish this.
This gets used in order to make the `disabled` field of `Guard` more
robust against future guard disablement reasons being added.
A test was also added to verify correct behaviour of the new type.
As per arti#175, we'd like to be able to handle newer Arti versions
storing additional state in the persisted state files, without dropping
this data on the floor when we write out changes to these files.
Use the #[serde(flatten)] mechanism to achieve this, by adding catch-all
HashMap<String, JsonValue> fields to all structs that are at risk of
this happening to them.
The limitations with toml seemed to be reaching a head, and I wasn't
able to refactor the guardmgr code enough to actually have its state
be serializable as toml. Json's limitations are much narrower.
Nick Mathewson
eta
Ian Jackson
Ian Jackson
Daniel Eades
Jani Monoses