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
Refactor Windows stdio and remove stdin double buffering
I was looking for something nice and small to work on, tried to tackle a few FIXME's in Windows stdio, and things grew from there.
This part of the standard library contains some tricky code, and has changed over the years to handle more corner cases. It could use some refactoring and extra comments.
Changes/fixes:
- Made `StderrRaw` `pub(crate)`, to remove the `Write` implementations on `sys::Stderr` (used unsynchronised for panic output).
- Remove the unused `Read` implementation on `sys::windows::stdin`
- The `windows::stdio::Output` enum made sense when we cached the handles, but we can use simple functions like `is_console` now that we get the handle on every read/write
- `write` can now calculate the number of written bytes as UTF-8 when we can't write all `u16`s.
- If `write` could only write one half of a surrogate pair, attempt another write for the other because user code can't reslice in any way that would allow us to write it otherwise.
- Removed the double buffering on stdin. Documentation on the unexposed `StdinRaw` says: 'This handle is not synchronized or buffered in any fashion'; which is now true.
- `sys::windows::Stdin` now always only partially fills its buffer, so we can guarantee any arbitrary UTF-16 can be re-encoded without losing any data.
- `sys::windows::STDIN_BUF_SIZE` is slightly larger to compensate. There should be no real change in the number of syscalls the buffered `Stdin` does. This buffer is a little larger, while the extra buffer on Stdin is gone.
- `sys::windows::Stdin` now attempts to handle unpaired surrogates at its buffer boundary.
- `sys::windows::Stdin` no langer allocates for its buffer, but the UTF-16 decoding still does.
### Testing
I did some manual testing of reading and writing to console. The console does support UTF-16 in some sense, but doesn't supporting displaying characters outside the BMP.
- compile stage 1 stdlib with a tiny value for `MAX_BUFFER_SIZE` to make it easier to catch corner cases
- run a simple test program that reads on stdin, and echo's to stdout
- write some lines with plenty of ASCII and emoji in a text editor
- copy and paste in console to stdin
- return with `\r\n\` or CTRL-Z
- copy and paste in text editor
- check it round-trips
-----
Fixes https://github.com/rust-lang/rust/issues/23344. All but one of the suggestions in that issue are now implemented. the missing one is:
> * When reading data, we require the entire set of input to be valid UTF-16. We should instead attempt to read as much of the input as possible as valid UTF-16, only returning an error for the actual invalid elements. For example if we read 10 elements, 5 of which are valid UTF-16, the 6th is bad, and then the remaining are all valid UTF-16, we should probably return the first 5 on a call to `read`, then return an error, then return the remaining on the next call to `read`.
Stdin in Console mode is dealing with text directly input by a user. In my opinion getting an unpaired surrogate is quite unlikely in that case, and a valid reason to error on the entire line of input (which is probably short). Dealing with it is incompatible with an unbuffered stdin, which seems the more interesting guarantee to me.
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
Implement checked_add_duration for SystemTime
[Original discussion on the rust user forum](https://users.rust-lang.org/t/std-systemtime-misses-a-checked-add-function/21785)
Since `SystemTime` is opaque there is no way to check if the result of an addition will be in bounds. That makes the `Add<Duration>` trait completely unusable with untrusted data. This is a big problem because adding a `Duration` to `UNIX_EPOCH` is the standard way of constructing a `SystemTime` from a unix timestamp.
This PR implements `checked_add_duration(&self, &Duration) -> Option<SystemTime>` for `std::time::SystemTime` and as a prerequisite also for all platform specific time structs. This also led to the refactoring of many `add_duration(&self, &Duration) -> SystemTime` functions to avoid redundancy (they now unwrap the result of `checked_add_duration`).
Some basic unit tests for the newly introduced function were added too.
I wasn't sure which stabilization attribute to add to the newly introduced function, so I just chose `#[stable(feature = "time_checked_add", since = "1.32.0")]` for now to make it compile. Please let me know how I should change it or if I violated any other conventions.
P.S.: I could only test on Linux so far, so I don't necessarily expect it to compile for all platforms.
Since SystemTime is opaque there is no way to check if the result
of an addition will be in bounds. That makes the Add<Duration>
trait completely unusable with untrusted data. This is a big problem
because adding a Duration to UNIX_EPOCH is the standard way of
constructing a SystemTime from a unix timestamp.
This commit implements checked_add_duration(&self, &Duration) -> Option<SystemTime>
for std::time::SystemTime and as a prerequisite also for all platform
specific time structs. This also led to the refactoring of many
add_duration(&self, &Duration) -> SystemTime functions to avoid
redundancy (they now unwrap the result of checked_add_duration).
Some basic unit tests for the newly introduced function were added
too.
Redox: Update to new changes
These are all cherry-picked from our fork:
- Remove the `env:` scheme
- Update `execve` system call to `fexec`
- Interpret shebangs: these are no longer handled by the kernel, which like usual tries to be as minimal as possible
This commit deletes the `alloc_system` crate from the standard
distribution. This unstable crate is no longer needed in the modern
stable global allocator world, but rather its functionality is folded
directly into the standard library. The standard library was already the
only stable location to access this crate, and as a result this should
not affect any stable code.
Replace push loops with extend() where possible
Or set the vector capacity where I couldn't do it.
According to my [simple benchmark](https://gist.github.com/ljedrz/568e97621b749849684c1da71c27dceb) `extend`ing a vector can be over **10 times** faster than `push`ing to it in a loop:
10 elements (6.1 times faster):
```
test bench_extension ... bench: 75 ns/iter (+/- 23)
test bench_push_loop ... bench: 458 ns/iter (+/- 142)
```
100 elements (11.12 times faster):
```
test bench_extension ... bench: 87 ns/iter (+/- 26)
test bench_push_loop ... bench: 968 ns/iter (+/- 3,528)
```
1000 elements (11.04 times faster):
```
test bench_extension ... bench: 311 ns/iter (+/- 9)
test bench_push_loop ... bench: 3,436 ns/iter (+/- 233)
```
Seems like a good idea to use `extend` as much as possible.
