Avoids:
```
warning: the following packages contain code that will be rejected by a future version of Rust: ntapi v0.3.7
note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 36`
```
This is a step towards making it Send+Sync.
I'm a little cagey about this in the long term, as there are some mux
operations that may technically require multiple fields to be locked for
their duration: allowing free-threaded access may introduce some subtle
(or not so subtle!) interleaving conditions where the overall mux state
is not yet consistent.
I'm thinking of prune_dead_windows kicking in while the mux is in the
middle of being manipulated.
I did try an initial pass of just moving everything under one lock, but
there is already quite a lot of mixed read/write access to different
aspects of the mux.
We'll see what bubbles up later!
Do it "more properly": use intrusive list linkage to manage three
indices:
* hash lookup
* recency
* frequency
eviction is frequency based, but in order to avoid things that were
super hot in the past and that are no longer hot clogging up the cache,
eviction will incrementally age out least recently used entries that
haven't been active in the span of some number of get/put operations.
Aging scales down the frequency value to reduce its strength, so an aged
item isn't necessarily immediately a candidate for removal, it just
makes it more likely to be picked up by the frequency based removal as
it goes unused for an extended period.
We were only using block_on from it, which we can call from the
underlying async_io crate.
Notably, removing async_std from the deps avoids async-global-executor
being pulled in and spawning nproc threads that are never used by
wezterm.
I spent a few hours in heap profilers. What I found was:
* Inefficient use of heap when building up runs of
`Action::Print(char)`.
-> Solve by adding `Action::PrintString(String)`
and accumulating utf8 bytes rather than u32 codepoints.
* Inefficient use of heap when building Quad buffers: the default
exponential growth of `Vec` tended to waste 40%-75% of the allocated
capacity, and since we could keep ~1024 of these in cache, there's
a lot of potential for waste.
-> Solve by bounding the growth to 64 at a time. This has similar
characteristics to exponential growth at the default 80x24 terminal
size. May need to add a config option for this step size for users
with very large terminals.
* Lazy eviction from the LFU caches. The underlying cache advisor is
somewhat probabilistic and has a minimum cache size of 256, making
it difficult to maintain low heap utilization.
-> Solve by replacing it with a very simple LFU algorithm. It doesn't
seem to hurt much at the default terminal size with the default
cache sizes. If we make the cache sizes smaller, its overhead is
reduced.
Some further experimentation is needed to adjust defaults, but this
should help reduce heap usage.
refs: https://github.com/wez/wezterm/issues/2626
I noticed from https://github.com/void-linux/void-packages/pull/36903
that 32-bit systems were failing to pass the test suite.
Running `cargo test --target i686-unknown-linux-gnu -- --nocapture
teeny_string` showed that we were faulting in the teenystring code
and digging a bit deeper showed that it was because our assumptions
about the high bits were wrong for 32-bit systems.
Fix this by making TeenyString based around a u64 rather than usize
so that we guarantee its size on all current systems.
