Stabilize CString::from_vec_with_nul[_unchecked]
Closes the tracking issue #73179. I am keeping this in _draft_ mode until the FCP has ended.
This is my first time stabilizing a feature, so I would appreciate any guidance on things I should do differently.
Closes#73179
Remove unnecessary condition in Barrier::wait()
This is my first pull request for Rust, so feel free to call me out if anything is amiss.
After some examination, I realized that the second condition of the "spurious-wakeup-handler" loop in ``std::sync::Barrier::wait()`` should always evaluate to ``true``, making it redundant in the ``&&`` expression.
Here is the affected function before the fix:
```rust
#[stable(feature = "rust1", since = "1.0.0")]
pub fn wait(&self) -> BarrierWaitResult {
let mut lock = self.lock.lock().unwrap();
let local_gen = lock.generation_id;
lock.count += 1;
if lock.count < self.num_threads {
// We need a while loop to guard against spurious wakeups.
// https://en.wikipedia.org/wiki/Spurious_wakeup
while local_gen == lock.generation_id && lock.count < self.num_threads { // fixme
lock = self.cvar.wait(lock).unwrap();
}
BarrierWaitResult(false)
} else {
lock.count = 0;
lock.generation_id = lock.generation_id.wrapping_add(1);
self.cvar.notify_all();
BarrierWaitResult(true)
}
}
```
At first glance, it seems that the check that ``lock.count < self.num_threads`` would be necessary in order for a thread A to detect when another thread B has caused the barrier to reach its thread count, making thread B the "leader".
However, the control flow implicitly results in an invariant that makes observing ``!(lock.count < self.num_threads)``, i.e. ``lock.count >= self.num_threads`` impossible from thread A.
When thread B, which will be the leader, calls ``.wait()`` on this shared instance of the ``Barrier``, it locks the mutex in the first line and saves the ``MutexGuard`` in the ``lock`` variable. It then increments the value of ``lock.count``. However, it then proceeds to check if ``lock.count < self.num_threads``. Since it is the leader, it is the case that (after the increment of ``lock.count``), the lock count is *equal* to the number of threads. Thus, the second branch is immediately taken and ``lock.count`` is zeroed. Additionally, the generation ID is incremented (with wrap). Then, the condition variable is signalled. But, the other threads are waiting at the line ``lock = self.cvar.wait(lock).unwrap();``, so they cannot resume until thread B's call to ``Barrier::wait()`` returns, which drops the ``MutexGuard`` acquired in the first ``let`` statement and unlocks the mutex.
The order of events is thus:
1. A thread A calls `.wait()`
2. `.wait()` acquires the mutex, increments `lock.count`, and takes the first branch
3. Thread A enters the ``while`` loop since the generation ID has not changed and the count is less than the number of threads for the ``Barrier``
3. Spurious wakeups occur, but both conditions hold, so the thread A waits on the condition variable
4. This process repeats for N - 2 additional times for non-leader threads A'
5. *Meanwhile*, Thread B calls ``Barrier::wait()`` on the same barrier that threads A, A', A'', etc. are waiting on. The thread count reaches the number of threads for the ``Barrier``, so all threads should now proceed, with B being the leader. B acquires the mutex and increments the value ``lock.count`` only to find that it is not less than ``self.num_threads``. Thus, it immediately clamps ``self.num_threads`` back down to 0 and increments the generation. Then, it signals the condvar to tell the A (prime) threads that they may continue.
6. The A, A', A''... threads wake up and attempt to re-acquire the ``lock`` as per the internal operation of a condition variable. When each A has exclusive access to the mutex, it finds that ``lock.generation_id`` no longer matches ``local_generation`` **and the ``&&`` expression short-circuits -- and even if it were to evaluate it, ``self.count`` is definitely less than ``self.num_threads`` because it has been reset to ``0`` by thread B *before* B dropped its ``MutexGuard``**.
Therefore, it my understanding that it would be impossible for the non-leader threads to ever see the second boolean expression evaluate to anything other than ``true``. This PR simply removes that condition.
Any input would be appreciated. Sorry if this is terribly verbose. I'm new to the Rust community and concurrency can be hard to explain in words. Thanks!
Reject octal zeros in IPv4 addresses
This fixes#86964 by rejecting octal zeros in IP addresses, such that `192.168.00.00000000` is rejected with a parse error, since having leading zeros in front of another zero indicates it is a zero written in octal notation, which is not allowed in the strict mode specified by RFC 6943 3.1.1. Octal rejection was implemented in #83652, but due to the way it was implemented octal zeros were still allowed.
Don't emit a warning for empty rmeta files.
This avoids displaying a warning when attempting to load an empty rmeta file. Warnings were enabled via #89634 which can cause a lot of noise (for example, running `./x.py check`). rustc generates empty rmeta files for things like binaries, which can happen when checking libraries as unittests.
Closes#89795
rustdoc: Box some fields of `GenericParamDefKind` to reduce size
This change shrinks `GenericParamDef` from 120 to 56 bytes. `GenericParamDef` is
used a lot, so the extra indirection should hopefully be worth the size savings.
r? `@ghost`
Warn on structs with a trailing zero-sized array but no `repr` attribute
Closes#2868
changelog: Implement ``[`trailing_empty_array`]``, which warns if a struct is defined where the last field is a zero-sized array but there are no `repr` attributes. Zero-sized arrays aren't very useful in Rust itself, so such a struct is likely being created to pass to C code or in some other situation where control over memory layout matters. Either way, a `repr` attribute is needed.
Merge the two depkind vtables
Knowledge of `DepKind`s is managed using two arrays containing flags (is_anon, eval_always, fingerprint_style), and function pointers (forcing and loading code).
This PR aims at merging the two arrays so as to reduce unneeded indirect calls and (hopefully) increase code locality.
r? `@ghost`
FIx FP in `missing_safety_doc` lint
Fix FP where lint souldn't fire if any parent has `#[doc(hidden)]` attribute
fixes: #7347
changelog: [`missing_safety_doc`] Fix FP if any parent has `#[doc(hidden)]` attribute
Erase late-bound regions before computing vtable debuginfo name.
Fixes#90019.
The `msvc_enum_fallback()` for computing enum type names needs to access the memory layout of niche enums in order to determine the type name. `compute_debuginfo_vtable_name()` did not properly erase regions before computing type names which made memory layout computation ICE when encountering un-erased regions.
r? `@wesleywiser`
resolve: Use `NameBinding` for local variables and generic parameters
`NameBinding` is a structure used for representing any name introduction (an item, or import, or even a built-in).
Except that local variables and generic parameters weren't represented as `NameBinding`s, for this reason they requires separate paths in name resolution code in several places.
This PR introduces `NameBinding`s for local variables as well and simplifies all the code working with them leaving only the `NameBinding` paths.
Add reference to another doc with explanation
Add reference to another doc that explains which repository should be passed in this command since this is not covered in the command help itself.
changelog: none
