The (unsafe) Mutex from sys_common had a rather complicated interface.
You were supposed to call init() manually, unless you could guarantee it
was neither moved nor used reentrantly.
Calling `destroy()` was also optional, although it was unclear if 1)
resources might be leaked or not, and 2) if destroy() should only be
called when `init()` was called.
This allowed for a number of interesting (confusing?) different ways to
use this Mutex, all captured in a single type.
In practice, this type was only ever used in two ways:
1. As a static variable. In this case, neither init() nor destroy() are
called. The variable is never moved, and it is never used
reentrantly. It is only ever locked using the LockGuard, never with
raw_lock.
2. As a Boxed variable. In this case, both init() and destroy() are
called, it will be moved and possibly used reentrantly.
No other combinations are used anywhere in `std`.
This change simplifies things by splitting this Mutex type into
two types matching the two use cases: StaticMutex and MovableMutex.
The interface of both new types is now both safer and simpler. The first
one does not call nor expose init/destroy, and the second one calls
those automatically in its new() and Drop functions. Also, the locking
functions of MovableMutex are no longer unsafe.
Remove std::io::lazy::Lazy in favour of SyncOnceCell
The (internal) std::io::lazy::Lazy was used to lazily initialize the stdout and stdin buffers (and mutexes). It uses atexit() to register a destructor to flush the streams on exit, and mark the streams as 'closed'. Using the stream afterwards would result in a panic.
Stdout uses a LineWriter which contains a BufWriter that will flush the buffer on drop. This one is important to be executed during shutdown, to make sure no buffered output is lost. It also forbids access to stdout afterwards, since the buffer is already flushed and gone.
Stdin uses a BufReader, which does not implement Drop. It simply forgets any previously read data that was not read from the buffer yet. This means that in the case of stdin, the atexit() function's only effect is making stdin inaccessible to the program, such that later accesses result in a panic. This is uncessary, as it'd have been safe to access stdin during shutdown of the program.
---
This change removes the entire io::lazy module in favour of SyncOnceCell. SyncOnceCell's fast path is much faster (a single atomic operation) than locking a sys_common::Mutex on every access like Lazy did.
However, SyncOnceCell does not use atexit() to drop the contained object during shutdown.
As noted above, this is not a problem for stdin. It simply means stdin is now usable during shutdown.
The atexit() call for stdout is moved to the stdio module. Unlike the now-removed Lazy struct, SyncOnceCell does not have a 'gone and unusable' state that panics. Instead of adding this again, this simply replaces the buffer with one with zero capacity. This effectively flushes the old buffer *and* makes any writes afterwards pass through directly without touching a buffer, making print!() available during shutdown without panicking.
---
In addition, because the contents of the SyncOnceCell are no longer dropped, we can now use `&'static` instead of `Arc` in `Stdout` and `Stdin`. This also saves two levels of indirection in `stdin()` and `stdout()`, since Lazy effectively stored a `Box<Arc<T>>`, and SyncOnceCell stores the `T` directly.
Rust vec bench import specific rand::RngCore
Using `RngCore` import for side effects is clearer than `*` which may bring it unnecessary more stuff than needed, it is also more explicit doing so.
@pickfire change `LEN = 16384` (and pos) and `once` instead of `[0].iter()` after this.
@rustbot modify labels: +C-cleanup +A-testsuite
Add `#![feature(const_fn_floating_point_arithmetic)]`
cc #76618
This is a template for splitting up `const_fn` into granular feature gates. I think this will make it easier, both for us and for users, to track stabilization of each individual feature. We don't *have* to do this, however. We could also keep stabilizing things out from under `const_fn`.
cc @rust-lang/wg-const-eval
r? @oli-obk
Explicitly document the size guarantees that Option makes.
Triggered by a discussion on wg-unsafe-code-guidelines about which layouts of `Option<T>` one can guarantee are optimised to a single pointer.
CC @RalfJung
Std/thread: deny unsafe op in unsafe fn
Partial fix of #73904.
This encloses `unsafe` operations in `unsafe fn` in `libstd/thread`.
`@rustbot` modify labels: F-unsafe-block-in-unsafe-fn
It's possible for method resolution to pick this method over a lower
priority stable method, causing compilation errors. Since this method
is permanently unstable, give it a name that is very unlikely to be used
in user code.
Make [].as_[mut_]ptr_range() (unstably) const.
Gated behind `const_ptr_offset`, as suggested by https://github.com/rust-lang/rust/issues/65807#issuecomment-697229404
This also marks `[].as_mut_ptr()` as const, because it's used by `as_mut_ptr_range`. I gated it behind the same feature, because I figured it's not worth adding a separate tracking issue for const `as_mut_ptr`.
BtreeMap: refactoring around edges
Parts chipped off a more daring effort, that the btree benchmarks judge to be performance-neutral.
r? @Mark-Simulacrum
Relax promises about condition variable.
For quite a while now, there have been plans to at some point use parking_lot or some other more efficient implementation of mutexes and condition variables. Right now, Mutex and CondVar both Box the 'real' mutex/condvar inside, to give it a stable address. This was done because implementations like pthread and Windows critical sections may not be moved. More efficient implementations based on futexes, WaitOnAddress, Windows SRW locks, parking_lot, etc. may be moved (while not borrowed), so wouldn't need boxing.
However, not boxing them (which would be great goal to achieve), breaks a promise std currently makes about CondVar. CondVar promises to panic when used with different mutexes, to ensure consistent behaviour on all platforms. To this check, a mutex is considered 'the same' if the address of the 'real mutex' in the Box is the same. This address doesn't change when moving a `std::mutex::Mutex` object, effectively giving it an identity that survives moves of the Mutex object. If we ever switch to a non-boxed version, they no longer carry such an identity, and this check can no longer be made.
Four options:
1. Always box mutexes.
2. Add a `MutexId` similar to `ThreadId`. Making mutexes bigger, and making it hard to ever have a `const fn new` for them.
3. Making the requirement of CondVar stricter: panic if the Mutex object itself moved.
4. Making the promise of CondVar weaker: don't promise to panic.
1, 2, and 3 seem like bad options. This PR updates the documentation for 4.
Use `Self` in docs when possible
Fixes#76542.
I used `rg '\s*//[!/]\s+fn [\w_]+\(&?self, ' .` in `library/` to find instances, I found some with that and some by manually checking.
@rustbot modify labels: C-enhancement T-doc
add array::from_ref
mirrors the methods in `std::slice` with the same name.
I guess this method previously didn't exist as there was close to no reason to create an array of size `1`.
This will change due to const generics in the near future.
Make delegation methods of `std::net::IpAddr` unstably const
Make the following methods of `std::net::IpAddr` unstable const under the `const_ip` feature:
- `is_unspecified`
- `is_loopback`
- `is_global`
- `is_multicast`
Also adds a test for these methods in a const context.
Possible because these methods delegate to the inner `Ipv4Addr` or `Ipv6Addr`, which were made const ([PR#76205](https://github.com/rust-lang/rust/pull/76142) and [PR#76206](https://github.com/rust-lang/rust/pull/76206)), and the recent stabilization of const control flow.
Part of #76205
r? @ecstatic-morse
The (internal) std::io::lazy::Lazy was used to lazily initialize the
stdout and stdin buffers (and mutexes). It uses atexit() to register a
destructor to flush the streams on exit, and mark the streams as
'closed'. Using the stream afterwards would result in a panic.
Stdout uses a LineWriter which contains a BufWriter that will flush the
buffer on drop. This one is important to be executed during shutdown,
to make sure no buffered output is lost. It also forbids access to
stdout afterwards, since the buffer is already flushed and gone.
Stdin uses a BufReader, which does not implement Drop. It simply forgets
any previously read data that was not read from the buffer yet. This
means that in the case of stdin, the atexit() function's only effect is
making stdin inaccessible to the program, such that later accesses
result in a panic. This is uncessary, as it'd have been safe to access
stdin during shutdown of the program.
---
This change removes the entire io::lazy module in favour of
SyncOnceCell. SyncOnceCell's fast path is much faster (a single atomic
operation) than locking a sys_common::Mutex on every access like Lazy
did.
However, SyncOnceCell does not use atexit() to drop the contained object
during shutdown.
As noted above, this is not a problem for stdin. It simply means stdin
is now usable during shutdown.
The atexit() call for stdout is moved to the stdio module. Unlike the
now-removed Lazy struct, SyncOnceCell does not have a 'gone and
unusable' state that panics. Instead of adding this again, this simply
replaces the buffer with one with zero capacity. This effectively
flushes the old buffer *and* makes any writes afterwards pass through
directly without touching a buffer, making print!() available during
shutdown without panicking.
revert const_type_id stabilization
This reverts #72488, which is currently on beta and scheduled to stabilize in `1.47.0`, based on https://github.com/rust-lang/rust/pull/75923#issuecomment-696676511
It turns out we might not be quite ready to stabilize `TypeId` in const contexts before having a chance to rework its internals. Since `TypeId` is a bit of an oddity we want to be careful about how those internals are currently being relied on while making changes. That will be easier to do without having to also consider compile-time contexts.
r? `@eddyb`
Rollup of 9 pull requests
Successful merges:
- #76898 (Record `tcx.def_span` instead of `item.span` in crate metadata)
- #76939 (emit errors during AbstractConst building)
- #76965 (Add cfg(target_has_atomic_equal_alignment) and use it for Atomic::from_mut.)
- #76993 (Changing the alloc() to accept &self instead of &mut self)
- #76994 (fix small typo in docs and comments)
- #77017 (Add missing examples on Vec iter types)
- #77042 (Improve documentation for ToSocketAddrs)
- #77047 (Miri: more informative deallocation error messages)
- #77055 (Add #[track_caller] to more panicking Cell functions)
Failed merges:
r? `@ghost`
Make the following methods of `std::net::IpAddr` unstable const under the `const_ip` feature:
- `is_unspecified`
- `is_loopback`
- `is_global`
- `is_multicast`
Also adds a test for these methods in a const context.
Possible because these methods delegate to the inner `Ipv4Addr` or `Ipv6Addr`, which were made const, and the recent stabilization of const control flow.
Part of #76205
Add #[track_caller] to more panicking Cell functions
Continuation of #74526
Adds the #[track_caller] attribute to almost all panicking Cell
functions. The ones that borrow two Cells in their function
body are spared, because the panic location helps pinpoint
which of the two borrows failed. You'd need to have
full debuginfo and backtraces enabled together with column
info in order to be able to discern the cases.
Column info in debuginfo is only available on non-Windows platforms.
Add cfg(target_has_atomic_equal_alignment) and use it for Atomic::from_mut.
Fixes some platform-specific problems with #74532 by using the actual alignment of the types instead of hardcoding a few `target_arch`s.
r? @RalfJung
Continuation of #74526
Adds the #[track_caller] attribute to almost all panicking Cell
functions. The ones that borrow two Cells in their function
body are spared, because the panic location helps pinpoint
which of the two borrows failed. You'd need to have
full debuginfo and backtraces enabled together with column
info in order to be able to discern the cases.
Column info is only available on non-Windows platforms.
Function to convert OpenOptions to c_int
Fixes: #74943
The creation_mode and access_mode function were already available in the OpenOptions struct, but currently private. I've added a new free functions to unix/fs.rs which takes the OpenOptions, and returns the c_int to be used as parameter for the `open` call.
Make some methods of `Pin` unstable const
Make the following methods unstable const under the `const_pin` feature:
- `new`
- `new_unchecked`
- `into_inner`
- `into_inner_unchecked`
- `get_ref`
- `into_ref`
- `get_mut`
- `get_unchecked_mut`
Of these, `into_inner` and `into_inner_unchecked` require the unstable `const_precise_live_drops`.
Also adds tests for these methods in a const context.
Tracking issue: #76654
r? @ecstatic-morse
Don't recommend ManuallyDrop to customize drop order
See
https://internals.rust-lang.org/t/need-for-controlling-drop-order-of-fields/12914/21
for the discussion.
TL;DR: ManuallyDrop is unsafe and footguny, but you can just ask the compiler to do all the work for you by re-ordering declarations.
Specifically, the original example from the docs is much better written as
```rust
struct Peach;
struct Banana;
struct Melon;
struct FruitBox {
melon: Melon,
// XXX: mind the relative drop order of the fields below
peach: Peach,
banana: Banana,
}
```
Remove duplicated library links between std and libc
The libc crate is already responsible for linking in the appropriate
libraries, and std doing the same thing results in duplicated library
names on the linker command line. Removing this duplication slightly
reduces linker time, and makes it simpler to adjust the set or order of
linked libraries in one place (such as to add static linking support).
Revert adding Atomic::from_mut.
This reverts #74532, which made too many assumptions about platforms, breaking some things.
Will need to be added later with a better way of gating on proper alignment, without hardcoding cfg(target_arch)s.
---
To be merged if fixing from_mut (#76965) takes too long.
r? @ghost
Add non-`unsafe` `.get_mut()` for `Unsafecell`
- Tracking issue: https://github.com/rust-lang/rust/issues/76943
As discussed in: https://internals.rust-lang.org/t/add-non-unsafe-get-mut-for-unsafecell/12407
- ### [Rendered documentation](https://modest-dubinsky-1f9f47.netlify.app/core/cell/struct.unsafecell)
This PR tries to move the sound `&mut UnsafeCell<T> -> &mut T` projection that all the "downstream" constructions were already relying on, up to the root abstraction, where it rightfully belongs, and officially blessing it.
- this **helps reduce the amount of `unsafe` snippets out there** (_c.f._, the second commit of this PR: 09503fd1b3)
The fact that this getter is now expose for `UnsafeCell<T>` itself, will also help convey the idea that **`UnsafeCell` is not magical _w.r.t._ `&mut` accesses**, contrary to what some people incorrectly think.
- Even the standard library itself at some point had such a confusion, _c.f._ this comment where there is a mention of multi-threaded (and thus _shared_) access despite dealing with exclusive references over unique ownership: 59fb88d061/library/core/src/cell.rs (L498-L499)
r? @RalfJung
Use intra-doc links in core/src/iter when possible
Helps with #75080.
I also updated lots of links to use `fn()` instead of `fn` when possible.
@rustbot modify labels: T-doc A-intra-doc-links
r? @jyn514
Stabilize some Option methods as const
Stabilize the following methods of `Option` as const:
- `is_some`
- `is_none`
- `as_ref`
These methods are currently const under the unstable feature `const_option` (tracking issue: #67441).
I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](https://github.com/rust-lang/rust/pull/75463).
Related: #76225
The libc crate is already responsible for linking in the appropriate
libraries, and std doing the same thing results in duplicated library
names on the linker command line. Removing this duplication slightly
reduces linker time, and makes it simpler to adjust the set or order of
linked libraries in one place (such as to add static linking support).
Avoid useless sift_down when std::collections::binary_heap::PeekMut is never mutably dereferenced
If `deref_mut` is never called then it's not possible for the element to be mutated without internal mutability, meaning there's no need to call `sift_down`.
This could be a little improvement in cases where you want to mutate the biggest element of the heap only if it satisfies a certain predicate that needs only read access to the element.
Remove MMX from Rust
Follow-up to https://github.com/rust-lang/stdarch/pull/890
This removes most of MMX from Rust (tests pass with small changes), keeping stable `is_x86_feature_detected!("mmx")` working.
Stabilize the following methods of `Option` as const:
- `is_some`
- `is_none`
- `as_ref`
Possible because of stabilization of #49146 (Allow if and match in constants).
Rollup of 15 pull requests
Successful merges:
- #76732 (Add docs for `BasicBlock`)
- #76832 (Let backends define custom targets)
- #76866 (Remove unused feature gates from library/ crates)
- #76875 (Move to intra-doc links in library/alloc/src/collections/binary_heap.rs)
- #76876 (Move to intra-doc links in collections/btree/map.rs and collections/linked_list.rs)
- #76877 (Move to intra-doc links in collections/vec_deque.rs and collections/vec_deque/drain.rs)
- #76878 (Move the version number to a plaintext file)
- #76883 (README.md: Remove prompts from code blocks)
- #76887 (Add missing examples on HashSet iter types)
- #76890 (use matches!() macro for simple if let conditions)
- #76891 (don't take `TyCtxt` by reference)
- #76910 (transmute: use diagnostic item)
- #76924 (Add tracking issue for feature(unix_socket_peek))
- #76926 (BTreeMap: code readability tweaks)
- #76940 (Don't allow implementing trait directly on type-alias-impl-trait)
Failed merges:
r? `@ghost`
transmute: use diagnostic item
closes#66075, we now have no remaining uses of `match_def_path` in the compiler while some uses still remain in `clippy`.
cc @RalfJung
Move to intra-doc links in collections/vec_deque.rs and collections/vec_deque/drain.rs
Helps with #75080.
@rustbot modify labels: T-doc, A-intra-doc-links
Remove unused feature gates from library/ crates
Removes some unused feature gates from library crates. It's likely not a complete list as I only tested a subset for which it's more likely that it is unused.
Stabilize some Result methods as const
Stabilize the following methods of Result as const:
- `is_ok`
- `is_err`
- `as_ref`
A test is also included, analogous to the test for `const_option`.
These methods are currently const under the unstable feature `const_result` (tracking issue: #67520).
I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](https://github.com/rust-lang/rust/pull/75463) and [PR#76135](https://github.com/rust-lang/rust/pull/76135).
Note: these methods are the only methods currently under the `const_result` feature, thus this PR results in the removal of the feature.
Related: #76225
This made too many assumptions about platforms, breaking some things.
Will need to be added later with a better way of gating on proper
alignment, without hardcoding cfg(target_arch)s.
support panic=abort in Miri
This is needed for https://github.com/rust-lang/miri/issues/1058 on Windows: we cannot run the inline-assembly versions of `abort`, so fall back to the intrinsic (which Miri supports).
Test and fix Send and Sync traits of BTreeMap artefacts
Fixes#76686.
I'm not quite sure what all this implies. E.g. comparing with the definitions for `NodeRef` in node.rs, maybe an extra bound `T: 'a` is useful for something. The test compiles on stable/beta (apart from `drain_filter`) so I bet `Sync` is equally desirable.
r? @Mark-Simulacrum
BTreeMap: wrap node's raw parent pointer in NonNull
Now that the other `*const` (root) is gone, seemed like a small step forward.
r? `@Mark-Simulacrum`
Add as_str() to string::Drain.
Vec's Drain recently [had its `.as_slice()` stabilized](https://github.com/rust-lang/rust/pull/72584), but String's Drain was still missing the analogous `.as_str()`. This adds that.
Also improves the Debug implementation, which now shows the remaining data instead of just `"Drain { .. }"`.
Add associated constant `BITS` to all integer types
Recently I've regularly come across this snippet (in a few different crates, including `core` and `std`):
```rust
std::mem::size_of<usize>() * 8
```
I think it's time for a `usize::BITS`.
do not inline black_box when building for Miri
We cannot do the assembly trick in Miri, but let's at least make sure MIR inlining does not circumvent the black_box.
Also use black_box instead of local optimization barriers in a few const tests.
deny(unsafe_op_in_unsafe_fn) in libstd/path.rs
The libstd/path.rs part of #73904 . Wraps the two calls to an unsafe fn Initializer::nop() in an unsafe block.
BTreeMap: avoid slices even more
Epilogue to #73971: it seems the compiler is unable to realize that creating a slice and `get_unchecked`-ing one element is a simple fetch. So try to spell it out for the only remaining but often invoked case.
Also, the previous code doesn't seem fair game to me, using `get_unchecked` to reach beyond the end of a slice. Although the local function `slice_insert` also does that.
r? `@Mark-Simulacrum`
Small cleanups in Windows Mutex.
- Move `held` into the boxed part, since the SRW lock implementation does not use this. This makes the Mutex 50% smaller.
- Use `Cell` instead of `UnsafeCell` for `held`, such that `.replace()` can be used.
- Add some comments.
- Avoid creating multiple `&mut`s to the critical section object in `ReentrantMutex`.
