Rollup merge of #99371 - ChrisDenton:simplify-gen-random-keys, r=thomcc

Remove synchronization from Windows `hashmap_random_keys`

Unfortunately using synchronization when generating hashmap keys can prevent it being used in `DllMain`.

~~Fixes #99341~~

library/std/src/sys/windows/rand.rs

@@ -1,62 +1,9 @@
 use crate::io;
 use crate::mem;
-use crate::sync;
+use crate::ptr;
 use crate::sys::c;
 
-/// The kinds of HashMap RNG that may be available
-#[derive(Clone, Copy, Debug, PartialEq)]
-enum HashMapRng {
-    Preferred,
-    Fallback,
-}
-
 pub fn hashmap_random_keys() -> (u64, u64) {
-    match get_hashmap_rng() {
-        HashMapRng::Preferred => {
-            preferred_rng().expect("couldn't generate random bytes with preferred RNG")
-        }
-        HashMapRng::Fallback => {
-            fallback_rng().expect("couldn't generate random bytes with fallback RNG")
-        }
-    }
-}
-
-/// Returns the HashMap RNG that should be used
-///
-/// Panics if they are both broken
-fn get_hashmap_rng() -> HashMapRng {
-    // Assume that if the preferred RNG is broken the first time we use it, it likely means
-    // that: the DLL has failed to load, there is no point to calling it over-and-over again,
-    // and we should cache the result
-    static VALUE: sync::OnceLock<HashMapRng> = sync::OnceLock::new();
-    *VALUE.get_or_init(choose_hashmap_rng)
-}
-
-/// Test whether we should use the preferred or fallback RNG
-///
-/// If the preferred RNG is successful, we choose it. Otherwise, if the fallback RNG is successful,
-/// we choose that
-///
-/// Panics if both the preferred and the fallback RNG are both non-functional
-fn choose_hashmap_rng() -> HashMapRng {
-    let preferred_error = match preferred_rng() {
-        Ok(_) => return HashMapRng::Preferred,
-        Err(e) => e,
-    };
-
-    match fallback_rng() {
-        Ok(_) => return HashMapRng::Fallback,
-        Err(fallback_error) => panic!(
-            "preferred RNG broken: `{}`, fallback RNG broken: `{}`",
-            preferred_error, fallback_error
-        ),
-    }
-}
-
-/// Generate random numbers using the preferred RNG function (BCryptGenRandom)
-fn preferred_rng() -> Result<(u64, u64), io::Error> {
-    use crate::ptr;
-
     let mut v = (0, 0);
     let ret = unsafe {
         c::BCryptGenRandom(
@@ -66,22 +13,23 @@ fn preferred_rng() -> Result<(u64, u64), io::Error> {
             c::BCRYPT_USE_SYSTEM_PREFERRED_RNG,
         )
     };
-
-    if ret == 0 { Ok(v) } else { Err(io::Error::last_os_error()) }
+    if ret != 0 { fallback_rng() } else { v }
 }
 
 /// Generate random numbers using the fallback RNG function (RtlGenRandom)
 #[cfg(not(target_vendor = "uwp"))]
-fn fallback_rng() -> Result<(u64, u64), io::Error> {
+#[inline(never)]
+fn fallback_rng() -> (u64, u64) {
     let mut v = (0, 0);
     let ret =
         unsafe { c::RtlGenRandom(&mut v as *mut _ as *mut u8, mem::size_of_val(&v) as c::ULONG) };
 
-    if ret != 0 { Ok(v) } else { Err(io::Error::last_os_error()) }
+    if ret != 0 { v } else { panic!("fallback RNG broken: {}", io::Error::last_os_error()) }
 }
 
 /// We can't use RtlGenRandom with UWP, so there is no fallback
 #[cfg(target_vendor = "uwp")]
-fn fallback_rng() -> Result<(u64, u64), io::Error> {
-    Err(io::const_io_error!(io::ErrorKind::Unsupported, "RtlGenRandom() not supported on UWP"))
+#[inline(never)]
+fn fallback_rng() -> (u64, u64) {
+    panic!("fallback RNG broken: RtlGenRandom() not supported on UWP");
 }