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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 09:22:09 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 09:22:09 +0000
commit43a97878ce14b72f0981164f87f2e35e14151312 (patch)
tree620249daf56c0258faa40cbdcf9cfba06de2a846 /third_party/rust/getrandom/src/util.rs
parentInitial commit. (diff)
downloadfirefox-43a97878ce14b72f0981164f87f2e35e14151312.tar.xz
firefox-43a97878ce14b72f0981164f87f2e35e14151312.zip
Adding upstream version 110.0.1.upstream/110.0.1upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/rust/getrandom/src/util.rs')
-rw-r--r--third_party/rust/getrandom/src/util.rs64
1 files changed, 64 insertions, 0 deletions
diff --git a/third_party/rust/getrandom/src/util.rs b/third_party/rust/getrandom/src/util.rs
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+// Copyright 2019 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+#![allow(dead_code)]
+use core::sync::atomic::{AtomicUsize, Ordering::Relaxed};
+
+// This structure represents a lazily initialized static usize value. Useful
+// when it is preferable to just rerun initialization instead of locking.
+// Both unsync_init and sync_init will invoke an init() function until it
+// succeeds, then return the cached value for future calls.
+//
+// Both methods support init() "failing". If the init() method returns UNINIT,
+// that value will be returned as normal, but will not be cached.
+//
+// Users should only depend on the _value_ returned by init() functions.
+// Specifically, for the following init() function:
+// fn init() -> usize {
+// a();
+// let v = b();
+// c();
+// v
+// }
+// the effects of c() or writes to shared memory will not necessarily be
+// observed and additional synchronization methods with be needed.
+pub struct LazyUsize(AtomicUsize);
+
+impl LazyUsize {
+ pub const fn new() -> Self {
+ Self(AtomicUsize::new(Self::UNINIT))
+ }
+
+ // The initialization is not completed.
+ pub const UNINIT: usize = usize::max_value();
+
+ // Runs the init() function at least once, returning the value of some run
+ // of init(). Multiple callers can run their init() functions in parallel.
+ // init() should always return the same value, if it succeeds.
+ pub fn unsync_init(&self, init: impl FnOnce() -> usize) -> usize {
+ // Relaxed ordering is fine, as we only have a single atomic variable.
+ let mut val = self.0.load(Relaxed);
+ if val == Self::UNINIT {
+ val = init();
+ self.0.store(val, Relaxed);
+ }
+ val
+ }
+}
+
+// Identical to LazyUsize except with bool instead of usize.
+pub struct LazyBool(LazyUsize);
+
+impl LazyBool {
+ pub const fn new() -> Self {
+ Self(LazyUsize::new())
+ }
+
+ pub fn unsync_init(&self, init: impl FnOnce() -> bool) -> bool {
+ self.0.unsync_init(|| init() as usize) != 0
+ }
+}