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rollup merge of #24908: inrustwetrust/once_memory_ordering

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`call_once` guarantees that there is a happens-before relationship between its closure and code following it via the sequentially consistent atomic store/loads of `self.cnt`.
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Alex Crichton 2015-04-29 15:45:45 -07:00
commit 0eaa811f4c
1 changed files with 5 additions and 1 deletions
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6
src/libstd/sync/once.rs
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@ -59,7 +59,11 @@ impl Once {
/// routine is currently running. /// routine is currently running.
/// ///
/// When this function returns, it is guaranteed that some initialization /// When this function returns, it is guaranteed that some initialization
/// has run and completed (it may not be the closure specified). /// has run and completed (it may not be the closure specified). It is also
/// guaranteed that any memory writes performed by the executed closure can
/// be reliably observed by other tasks at this point (there is a
/// happens-before relation between the closure and code executing after the
/// return).
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn call_once<F>(&'static self, f: F) where F: FnOnce() { pub fn call_once<F>(&'static self, f: F) where F: FnOnce() {
// Optimize common path: load is much cheaper than fetch_add. // Optimize common path: load is much cheaper than fetch_add.