| // 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}; |
| } |
| } |
