Rollup merge of #76979 - fusion-engineering-forks:windows-fallback-check, r=dtolnay
Improve std::sys::windows::compat Improves the compat_fn macro in sys::windows, which is used for conditionally loading APIs that might not be available. - The module (dll) name can now be any string, not just an ident. (Not all Windows api modules are valid Rust identifiers. E.g. `WaitOnAddress` comes from `API-MS-Win-Core-Synch-l1-2-0.dll`.) - Adds `FuncName::is_available()` for checking if a function is really available without having to do a duplicate lookup. - Add comment explaining the lack of locking. - Use `$_:block` to simplify the macro_rules. - Apply `allow(unused_variables)` only to the fallback instead of everything. --- The second point (`is_available()`) simplifies code that needs to pick an implementation depening on what is available, like `sys/windows/mutex.rs`. Before this change, it'd do its own lookup and keep its own `AtomicUsize` to track the result. Now it can just use `c::AcquireSRWLockExclusive::is_available()` directly. This will also be useful when park/unpark/CondVar/etc. get improved implementations (e.g. from parking_lot or something else), as the best APIs for those are not available before Windows 8.
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00b3450bbc
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@ -1032,7 +1032,7 @@ extern "system" {
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// Functions that aren't available on every version of Windows that we support,
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// but we still use them and just provide some form of a fallback implementation.
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compat_fn! {
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kernel32:
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"kernel32":
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pub fn CreateSymbolicLinkW(_lpSymlinkFileName: LPCWSTR,
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_lpTargetFileName: LPCWSTR,
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@ -12,7 +12,6 @@
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//! function is available but afterwards it's just a load and a jump.
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use crate::ffi::CString;
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use crate::sync::atomic::{AtomicUsize, Ordering};
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use crate::sys::c;
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pub fn lookup(module: &str, symbol: &str) -> Option<usize> {
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@ -28,45 +27,69 @@ pub fn lookup(module: &str, symbol: &str) -> Option<usize> {
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}
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}
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pub fn store_func(ptr: &AtomicUsize, module: &str, symbol: &str, fallback: usize) -> usize {
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let value = lookup(module, symbol).unwrap_or(fallback);
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ptr.store(value, Ordering::SeqCst);
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value
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}
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macro_rules! compat_fn {
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($module:ident: $(
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($module:literal: $(
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$(#[$meta:meta])*
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pub fn $symbol:ident($($argname:ident: $argtype:ty),*)
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-> $rettype:ty {
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$($body:expr);*
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}
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pub fn $symbol:ident($($argname:ident: $argtype:ty),*) -> $rettype:ty $body:block
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)*) => ($(
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#[allow(unused_variables)]
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$(#[$meta])*
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pub unsafe fn $symbol($($argname: $argtype),*) -> $rettype {
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pub mod $symbol {
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use super::*;
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use crate::sync::atomic::{AtomicUsize, Ordering};
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use crate::mem;
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type F = unsafe extern "system" fn($($argtype),*) -> $rettype;
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static PTR: AtomicUsize = AtomicUsize::new(0);
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#[allow(unused_variables)]
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unsafe extern "system" fn fallback($($argname: $argtype),*) -> $rettype $body
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/// This address is stored in `PTR` to incidate an unavailable API.
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///
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/// This way, call() will end up calling fallback() if it is unavailable.
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///
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/// This is a `static` to avoid rustc duplicating `fn fallback()`
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/// into both load() and is_available(), which would break
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/// is_available()'s comparison. By using the same static variable
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/// in both places, they'll refer to the same (copy of the)
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/// function.
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///
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/// LLVM merging the address of fallback with other functions
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/// (because of unnamed_addr) is fine, since it's only compared to
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/// an address from GetProcAddress from an external dll.
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static FALLBACK: F = fallback;
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#[cold]
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fn load() -> usize {
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crate::sys::compat::store_func(&PTR,
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stringify!($module),
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stringify!($symbol),
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fallback as usize)
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}
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unsafe extern "system" fn fallback($($argname: $argtype),*)
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-> $rettype {
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$($body);*
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// There is no locking here. It's okay if this is executed by multiple threads in
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// parallel. `lookup` will result in the same value, and it's okay if they overwrite
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// eachothers result as long as they do so atomically. We don't need any guarantees
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// about memory ordering, as this involves just a single atomic variable which is
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// not used to protect or order anything else.
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let addr = crate::sys::compat::lookup($module, stringify!($symbol))
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.unwrap_or(FALLBACK as usize);
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PTR.store(addr, Ordering::Relaxed);
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addr
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}
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let addr = match PTR.load(Ordering::SeqCst) {
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fn addr() -> usize {
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match PTR.load(Ordering::Relaxed) {
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0 => load(),
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n => n,
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};
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mem::transmute::<usize, F>(addr)($($argname),*)
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addr => addr,
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}
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}
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#[allow(dead_code)]
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pub fn is_available() -> bool {
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addr() != FALLBACK as usize
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}
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pub unsafe fn call($($argname: $argtype),*) -> $rettype {
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mem::transmute::<usize, F>(addr())($($argname),*)
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}
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}
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pub use $symbol::call as $symbol;
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)*)
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}
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@ -23,7 +23,6 @@ use crate::cell::{Cell, UnsafeCell};
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use crate::mem::{self, MaybeUninit};
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use crate::sync::atomic::{AtomicUsize, Ordering};
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use crate::sys::c;
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use crate::sys::compat;
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pub struct Mutex {
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// This is either directly an SRWLOCK (if supported), or a Box<Inner> otherwise.
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@ -40,8 +39,8 @@ struct Inner {
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#[derive(Clone, Copy)]
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enum Kind {
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SRWLock = 1,
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CriticalSection = 2,
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SRWLock,
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CriticalSection,
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}
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#[inline]
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@ -130,21 +129,7 @@ impl Mutex {
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}
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fn kind() -> Kind {
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static KIND: AtomicUsize = AtomicUsize::new(0);
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let val = KIND.load(Ordering::SeqCst);
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if val == Kind::SRWLock as usize {
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return Kind::SRWLock;
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} else if val == Kind::CriticalSection as usize {
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return Kind::CriticalSection;
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}
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let ret = match compat::lookup("kernel32", "AcquireSRWLockExclusive") {
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None => Kind::CriticalSection,
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Some(..) => Kind::SRWLock,
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};
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KIND.store(ret as usize, Ordering::SeqCst);
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ret
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if c::AcquireSRWLockExclusive::is_available() { Kind::SRWLock } else { Kind::CriticalSection }
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}
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pub struct ReentrantMutex {
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