Add implementations of last in terms of next_back on a bunch of DoubleEndedIterators
Provided a `DoubleEndedIterator` has finite length, `Iterator::last` is equivalent to `DoubleEndedIterator::next_back`. But searching forwards through the iterator when it's unnecessary is obviously not good for performance. I ran into this on one of the collection iterators.
I tried adding appropriate overloads for a bunch of the iterator adapters like filter, map, etc, but I ran into a lot of type inference failures after doing so.
The other interesting case is what to do with `Repeat`. Do we consider it part of the contract that `Iterator::last` will loop forever on it? The docs do say that the iterator will be evaluated until it returns None. This is also relevant for the adapters, it's trivially easy to observe whether a `Map` adapter invoked its closure a zillion times or just once for the last element.
This renames `std::io::IoVec` to `std::io::IoSlice` and
`std::io::IoVecMut` to `std::io::IoSliceMut`, and stabilizes
`std::io::IoSlice`, `std::io::IoSliceMut`,
`std::io::Read::read_vectored`, and `std::io::Write::write_vectored`.
Closes#58452
std: Add `{read,write}_vectored` for more types
This commit implements the `{read,write}_vectored` methods on more types
in the standard library, namely:
* `std::fs::File`
* `std::process::ChildStd{in,out,err}`
* `std::io::Std{in,out,err}`
* `std::io::Std{in,out,err}Lock`
* `std::io::Std{in,out,err}Raw`
Where supported the OS implementations hook up to native support,
otherwise it falls back to the already-defaulted implementation.
This commit implements the `{read,write}_vectored` methods on more types
in the standard library, namely:
* `std::fs::File`
* `std::process::ChildStd{in,out,err}`
* `std::io::Std{in,out,err}`
* `std::io::Std{in,out,err}Lock`
* `std::io::Std{in,out,err}Raw`
Where supported the OS implementations hook up to native support,
otherwise it falls back to the already-defaulted implementation.
This commit removes usage of `Once` from the internal implementation of
time utilities on OSX and Windows. It turns out that we accidentally hit
a deadlock today (#59020) via events that look like:
* A thread invokes `park_timeout`
* Internally, only on OSX, `park_timeout` calls `Instant::elapsed`
* Inside of `Instant::elapsed` on OSX we enter a `Once` to initialize
global timer data
* Inside of `Once`, it attempts to `park`
This means on the same stack frame, when there's contention, we're
calling `park` from inside `park_timeout`, causing a deadlock!
The solution implemented in this commit was to remove usage of `Once`
and instead just do a small dance with atomics. There's no real need we
need to guarantee that the global information is only learned once, only
that it's only *stored* once. This implementation may have multiple
threads invoke `mach_timebase_info`, but only one will store the global
information which will amortize the cost for all other threads.
A similar fix has been applied to windows to be uniform across our
implementations, but looking at the code on Windows no deadlock was
possible. This is purely just a consistency update for Windows and in
theory a slightly leaner implementation.
Closes#59020
Set secure flags when opening a named pipe on Windows
Fixes https://github.com/rust-lang/rust/issues/42036, see also the previous attempt in https://github.com/rust-lang/rust/pull/44556.
Whether this is correct depends on if it is somehow possible to create a symlink to a named pipe, outside the named pipe filesystem (NPFS). But as far as I can tell that should be impossible.
Also fixes that `security_qos_flags(SECURITY_ANONYMOUS)` does not set the `SECURITY_SQOS_PRESENT` flag, and the incorrect documentation about the default value of `security_qos_flags`.
Add vectored read and write support
This functionality has lived for a while in the tokio ecosystem, where
it can improve performance by minimizing copies.
r? @alexcrichton
Per review comments, this commit switches out the backing
type for Instant on windows to a Duration. Tests all pass,
and the code's a lot simpler (plus it should be portable now,
with the exception of the QueryPerformanceWhatever functions).
Right now we do unit conversions between PerfCounter measurements
and nanoseconds for every add/sub we do between Durations and Instants
on Windows machines. This leads to goofy behavior, like this snippet
failing:
```
let now = Instant::now();
let offset = Duration::from_millis(5);
assert_eq!((now + offset) - now, (now - now) + offset);
```
with precision problems like this:
```
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `4.999914ms`,
right: `5ms`', src\main.rs:6:5
```
To fix it, this changeset does the unit conversion once, when we
measure the clock, and all the subsequent math in u64 nanoseconds.
It also adds an exact associativity test to the `sys/time.rs`
test suite to make sure we don't regress on this in the future.
On Windows process exit codes are never signals but rather always 32-bit
integers. Most faults like segfaults and such end up having large
integers used to represent them, like STATUS_ACCESS_VIOLATION being
0xC0000005. Currently, however, when an `ExitStatus` is printed this
ends up getting rendered as 3221225477 which is somewhat more difficult
to debug.
This commit adds a branch in `Display for ExitStatus` on Windows which
handles exit statuses where the high bit is set and prints those exit
statuses as hex instead of with decimals. This will hopefully preserve
the current display for small exit statuses (like `exit code: 22`), but
assist in quickly debugging segfaults/access violations/etc. I've
found at least that the hex codes are easier to search for than decimal.
I wasn't able to find any official documentation saying that all system
exit codes have the high bit set, but I figure it's a good enough
heuristic for now.
This commit is an attempt to force `Instant::now` to be monotonic
through any means possible. We tried relying on OS/hardware/clock
implementations, but those seem buggy enough that we can't rely on them
in practice. This commit implements the same hammer Firefox recently
implemented (noted in #56612) which is to just keep whatever the lastest
`Instant::now()` return value was in memory, returning that instead of
the OS looks like it's moving backwards.
Closes#48514Closes#49281
cc #51648
cc #56560Closes#56612Closes#56940
Add checked_add method to Instant time type
Appending functionality to the already opened topic of `checked_add` on time types over at #55940.
Doing checked addition between an `Instant` and a `Duration` is important to reliably determine a future instant. We could use this in the `parking_lot` crate to compute an instant when in the future to wake a thread up without risking a panic.
Steven Fackler