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// A "once" is a relatively simple primitive, and it's also typically provided
// by the OS as well (see `pthread_once` or `InitOnceExecuteOnce`). The OS
// primitives, however, tend to have surprising restrictions, such as the Unix
// one doesn't allow an argument to be passed to the function.
//
// As a result, we end up implementing it ourselves in the standard library.
// This also gives us the opportunity to optimize the implementation a bit which
// should help the fast path on call sites.
cfg_if::cfg_if! {
if #[cfg(any(
target_os = "linux",
target_os = "android",
all(target_arch = "wasm32", target_feature = "atomics"),
target_os = "freebsd",
target_os = "openbsd",
target_os = "dragonfly",
target_os = "fuchsia",
target_os = "hermit",
))] {
mod futex;
pub use futex::{Once, OnceState};
} else if #[cfg(any(
windows,
target_family = "unix",
all(target_vendor = "fortanix", target_env = "sgx"),
target_os = "solid_asp3",
))] {
mod queue;
pub use queue::{Once, OnceState};
} else {
pub use crate::sys::once::{Once, OnceState};
}
}
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