Consolidate sigemptyset workarounds
In sys/unix/process, we work around the sigemptyset linking issues
on android in two different ways. This change consolidates these
workarounds, and avoids duplicating bindings from `libc`.
avoid unnecessary reservations in std::io::Take::read_to_end
Prevously the `read_to_end` implementation for `std::io::Take` used its
own `limit` as a cap on the `reservation_size`. However, that could
still result in an over-allocation like this:
1. Call `reader.take(5).read_to_end(&mut vec)`.
2. `read_to_end_with_reservation` reserves 5 bytes and calls `read`.
3. `read` writes 5 bytes.
4. `read_to_end_with_reservation` reserves 5 bytes and calls `read`.
5. `read` writes 0 bytes.
6. The read loop ends with `vec` having length 5 and capacity 10.
The reservation of 5 bytes was correct for the read at step 2 but
unnecessary for the read at step 4. By that second read, `Take::limit`
is 0, but the `read_to_end_with_reservation` loop is still using the
same `reservation_size` it started with.
Solve this by having `read_to_end_with_reservation` take a closure,
which lets it get a fresh `reservation_size` for each read. This is an
implementation detail which doesn't affect any public API.
In sys/unix/process, we work around the sigemptyset linking issues
on android in two different ways. This change consolidates these
workarounds, and avoids duplicating bindings from `libc`.
This commit updates the `backtrace` crate from 0.3.34 to 0.3.35. The
[included set of changes][changes] for this update mostly includes some
gimli-related improvements (not relevant for the standard library) but
critically includes a fix for rust-lang/backtrace-rs#230. The standard
library will not aqcuire a session-local lock whenever a backtrace is
generated on Windows to allow external synchronization with the
`backtrace` crate itself, allowing `backtrace` to be safely used while
other threads may be panicking.
[changes]: https://github.com/rust-lang/backtrace-rs/compare/0.3.34...0.3.35
… and add a separately-unstable field to force non-exhaustive matching
(`#[non_exhaustive]` is no implemented yet on enum variants)
so that we have the option to later expose the allocator’s error value.
CC https://github.com/rust-lang/wg-allocators/issues/23
