Windows: Make stdin pipes synchronous
Stdin pipes do not need to be used asynchronously within the standard library. This is a first step in making pipes mostly synchronous.
r? `@m-ou-se`
std: directly use pthread in UNIX parker implementation
`Mutex` and `Condvar` are being replaced by more efficient implementations, which need thread parking themselves (see #93740). Therefore we should use the `pthread` synchronization primitives directly. Also, we can avoid allocating the mutex and condition variable because the `Parker` struct is being placed in an `Arc` anyways.
This basically is just a copy of the current `Mutex` and `Condvar` code, which will however be removed (again, see #93740). An alternative implementation could be to use dedicated private `OsMutex` and `OsCondvar` types, but all the other platforms supported by std actually have their own thread parking primitives.
I used `Pin` to guarantee a stable address for the `Parker` struct, while the current implementation does not, rather using extra unsafe declaration. Since the thread struct is shared anyways, I assumed this would not add too much clutter while being clearer.
Mutex and Condvar are being replaced by more efficient implementations, which need thread parking themselves (see #93740). Therefore use the pthread synchronization primitives directly. Also, avoid allocating because the Parker struct is being placed in an Arc anyways.
Windows Command: Don't run batch files using verbatim paths
Fixes#95178
Note that the first commit does some minor refactoring (moving command line argument building to args.rs). The actual changes are in the second.
Reduce allocations for path conversions on Windows
Previously, UTF-8 to UTF-16 Path conversions on Windows unnecessarily allocate twice, as described in #96297. This commit fixes that issue.
Improve Windows path prefix parsing
This PR fixes improves parsing of Windows path prefixes. `parse_prefix` now supports both types of separators on Windows (`/` and `\`).
[fuchsia] Add implementation for `current_exe`
This implementation returns a best attempt at the current exe path. On
fuchsia, fdio will always use `argv[0]` as the process name and if it is
not set then an error will be returned. Because this is not guaranteed
to be the case, this implementation returns an error if `argv` does not
contain any elements.
remove_dir_all_recursive: treat ELOOP the same as ENOTDIR
On older Linux kernels (I tested on 4.4, corresponding to Ubuntu 16.04), opening a symlink using `O_DIRECTORY | O_NOFOLLOW` returns `ELOOP` instead of `ENOTDIR`. We should handle it the same, since a symlink is still not a directory and needs to be `unlink`ed.
Use sys::unix::locks::futex* on wasm+atomics.
This removes the wasm-specific lock implementations and instead re-uses the implementations from sys::unix.
Tracking issue: https://github.com/rust-lang/rust/issues/93740
cc ``@alexcrichton``
This implementation returns a best attempt at the current exe path. On
fuchsia, fdio will always use `argv[0]` as the process name and if it is
not set then an error will be returned. Because this is not guaranteed
to be the case, this implementation returns an error if `argv` does not
contain any elements.
Use a single ReentrantMutex implementation on all platforms.
This replaces all platform specific ReentrantMutex implementations by the one I added in #95727 for Linux, since that one does not depend on any platform specific details.
r? `@Amanieu`
fix error handling for pthread_sigmask(3)
Errors from `pthread_sigmask(3)` were handled using `cvt()`, which expects a return value of `-1` on error and uses `errno`.
However, `pthread_sigmask(3)` returns `0` on success and an error number otherwise.
Fix it by replacing `cvt()` with `cvt_nz()`.
Use u32 instead of i32 for futexes.
This changes futexes from i32 to u32. The [Linux man page](https://man7.org/linux/man-pages/man2/futex.2.html) uses `uint32_t` for them, so I'm not sure why I used i32 for them. Maybe because I first used them for thread parkers, where I used -1, 0, and 1 as the states.
(Wasm's `memory.atomic.wait32` does use `i32`, because wasm doesn't support `u32`.)
It doesn't matter much, but using the unsigned type probably results in fewer surprises when shifting bits around or using comparison operators.
r? ```@Amanieu```
Windows: Use a pipe relay for chaining pipes
Fixes#95759
This fixes the issue by chaining pipes synchronously and manually pumping messages between them. It's not ideal but it has the advantage of not costing anything if pipes are not chained ("don't pay for what you don't use") and it also avoids breaking existing code that rely on our end of the pipe being asynchronous (which includes rustc's own testing framework).
Libraries can avoid needing this by using their own pipes to chain commands.
Replace RwLock by a futex based one on Linux
This replaces the pthread-based RwLock on Linux by a futex based one.
This implementation is similar to [the algorithm](https://gist.github.com/kprotty/3042436aa55620d8ebcddf2bf25668bc) suggested by `@kprotty,` but modified to prefer writers and spin before sleeping. It uses two futexes: One for the readers to wait on, and one for the writers to wait on. The readers futex contains the state of the RwLock: The number of readers, a bit indicating whether writers are waiting, and a bit indicating whether readers are waiting. The writers futex is used as a simple condition variable and its contents are meaningless; it just needs to be changed on every notification.
Using two futexes rather than one has the obvious advantage of allowing a separate queue for readers and writers, but it also means we avoid the problem a single-futex RwLock would have of making it hard for a writer to go to sleep while the number of readers is rapidly changing up and down, as the writers futex is only changed when we actually want to wake up a writer.
It always prefers writers, as we decided [here](https://github.com/rust-lang/rust/issues/93740#issuecomment-1070696128).
To be able to prefer writers, it relies on futex_wake to return the number of awoken threads to be able to handle write-unlocking while both the readers-waiting and writers-waiting bits are set. Instead of waking both and letting them race, it first wakes writers and only continues to wake the readers too if futex_wake reported there were no writers to wake up.
r? `@Amanieu`
