Run fixpoint per strongly connected component (#999)

* Run nested cycles in a single fixpoint iteration

Fix serde attribute

* Remove inline from `validate_same_iteration`

* Nits

* Move locking into sync table

* More trying

* More in progress work

* More progress

* Fix most parallel tests

* More bugfixes

* Short circuit in some cases

* Short circuit in drop

* Delete some unused code

* A working solution

* Simplify more

* Avoid repeated query lookups in `transfer_lock`

* Use recursion for unblocking

* Fix hang in `maybe_changed_after`

* Move claiming of transferred memos into a separate function

* More aggressive use of attributes

* Make re-entrant a const parameter

* Smaller clean-ups

* Only collect cycle heads one level deep

* More cleanups

* More docs

* More comments

* More documentation, cleanups

* More documentation, cleanups

* Remove inline attribute

* Fix failing tracked structs test

* Fix panic

* Fix persistence test

* Add test for panic in nested cycle

* Allow cycle initial values same-stack

* Try inlining fetch

* Remove some inline attributes

* Add safety comment

* Clippy

* Panic if `provisional_retry` runs too many times

* Better handling of panics in cycles

* Don't use const-generic for `REENTRANT`

* More nit improvements

* Remove `IterationCount::panicked`

* Prefer outer most cycles in `outer_cycle`

* Code review feedback

* Iterate only once in panic test when running with miri

Author: MichaReiser

Cargo.toml

@@ -22,7 +22,7 @@ intrusive-collections = "0.9.7"
 parking_lot = "0.12"
 portable-atomic = "1"
 rustc-hash = "2"
-smallvec = "1"
+smallvec = { version = "1", features = ["const_new"] }
 thin-vec = { version = "0.2.14" }
 tracing = { version = "0.1", default-features = false, features = ["std"] }
 

src/active_query.rs

@@ -498,7 +498,7 @@ impl fmt::Display for Backtrace {
             if full {
                 write!(fmt, " -> ({changed_at:?}, {durability:#?}")?;
                 if !cycle_heads.is_empty() || !iteration_count.is_initial() {
-                    write!(fmt, ", iteration = {iteration_count:?}")?;
+                    write!(fmt, ", iteration = {iteration_count}")?;
                 }
                 write!(fmt, ")")?;
             }
@@ -517,7 +517,7 @@ impl fmt::Display for Backtrace {
                         }
                         write!(
                             fmt,
-                            "{:?} -> {:?}",
+                            "{:?} -> iteration = {}",
                             head.database_key_index, head.iteration_count
                         )?;
                     }

src/cancelled.rs

@@ -20,6 +20,7 @@ pub enum Cancelled {
 }
 
 impl Cancelled {
+    #[cold]
     pub(crate) fn throw(self) -> ! {
         // We use resume and not panic here to avoid running the panic
         // hook (that is, to avoid collecting and printing backtrace).