util: Remove unused spin-lock interfaces

We no longer use spin-locks anywhere in getrandom, so remove any
interfaces which spin.

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

src/util.rs

@@ -35,8 +35,6 @@ impl LazyUsize {
 
     // The initialization is not completed.
     pub const UNINIT: usize = usize::max_value();
-    // The initialization is currently running.
-    pub const ACTIVE: usize = usize::max_value() - 1;
 
     // Runs the init() function at least once, returning the value of some run
     // of init(). Multiple callers can run their init() functions in parallel.
@@ -50,36 +48,6 @@ impl LazyUsize {
         }
         val
     }
-
-    // Synchronously runs the init() function. Only one caller will have their
-    // init() function running at a time, and exactly one successful call will
-    // be run. init() returning UNINIT or ACTIVE will be considered a failure,
-    // and future calls to sync_init will rerun their init() function.
-    pub fn sync_init(&self, init: impl FnOnce() -> usize, mut wait: impl FnMut()) -> usize {
-        // Common and fast path with no contention. Don't wast time on CAS.
-        match self.0.load(Relaxed) {
-            Self::UNINIT | Self::ACTIVE => {}
-            val => return val,
-        }
-        // Relaxed ordering is fine, as we only have a single atomic variable.
-        loop {
-            match self.0.compare_and_swap(Self::UNINIT, Self::ACTIVE, Relaxed) {
-                Self::UNINIT => {
-                    let val = init();
-                    self.0.store(
-                        match val {
-                            Self::UNINIT | Self::ACTIVE => Self::UNINIT,
-                            val => val,
-                        },
-                        Relaxed,
-                    );
-                    return val;
-                }
-                Self::ACTIVE => wait(),
-                val => return val,
-            }
-        }
-    }
 }
 
 // Identical to LazyUsize except with bool instead of usize.

src/util_libc.rs

@@ -98,37 +98,6 @@ impl Weak {
     }
 }
 
-pub struct LazyFd(LazyUsize);
-
-impl LazyFd {
-    pub const fn new() -> Self {
-        Self(LazyUsize::new())
-    }
-
-    // If init() returns Some(x), x should be nonnegative.
-    pub fn init(&self, init: impl FnOnce() -> Option<libc::c_int>) -> Option<libc::c_int> {
-        let fd = self.0.sync_init(
-            || match init() {
-                // OK as val >= 0 and val <= c_int::MAX < usize::MAX
-                Some(val) => val as usize,
-                None => LazyUsize::UNINIT,
-            },
-            || unsafe {
-                // We are usually waiting on an open(2) syscall to complete,
-                // which typically takes < 10us if the file is a device.
-                // However, we might end up waiting much longer if the entropy
-                // pool isn't initialized, but even in that case, this loop will
-                // consume a negligible amount of CPU on most platforms.
-                libc::usleep(10);
-            },
-        );
-        match fd {
-            LazyUsize::UNINIT => None,
-            val => Some(val as libc::c_int),
-        }
-    }
-}
-
 cfg_if! {
     if #[cfg(any(target_os = "linux", target_os = "emscripten"))] {
         use libc::open64 as open;