The `is_sync::<T>()` runtime check relied on implicit specialization via
`Copy`/`Clone` array behavior, which has changed in Rust 1.86+.
`UserDataRef` always taking an exclusive lock even for `Sync` userdata,
preventing concurrent shared borrows.
With the `send` feature flag enabled, userdata types must now be `Send + Sync`.
This is a breaking change, `T: Send + !Sync` userdata types can be wrapped in a `Mutex`
or used inside a `Scope` where this restriction is lifted.
Instead of locking the VM and making a copy on auxiliary thread, track number of references using Rust ref counter.
This should also help reducing number of used references (they are limited to to 1M usually) on auxiliary thread.
Before this change, Lua GC was responsible to collect and destroy the future if
`AsyncThread` dropped in yielded state.
Now we will propagate "drop" event immediately so Lua GC need to only free the memory.
We need this because they have different requirements:
- Thread creation callback can return Error or panic
- Thread collection callback runs during Luau GC cycle and cannot make any Lua calls or trigger panics.
- Support global hooks inherited by new threads
- Support thread hooks, where each thread can have its own hook
This should also allow to enable hooks for async calls.
Related to #489#347
- Store single `AtomicI32` field instead of pair i32,AtomicBool
- Make creation faster by skipping intermediate `Value` layer
Add new `RegistryKey::id()` method to return underlying identifier
Rewrite using the new `push_into_stack()`/`from_stack()` methods.
Also store thread state (pointer) in `Thread` struct to avoid getting it every time.
Async userdata methods still need to have arguments stored in ref thread as stack is empty on every poll().
They allow to push Value directly to Lua stack or get Value from Lua stack without creating MultiValue container.
This approach is a big optimization opportunity and already demonstrated great results.
For instance, obtaining `&T` for userdata methods are now work directly from stack value without copying to auxiliary stack.
Alex Orlenko