diff options
Diffstat (limited to 'library/std/src/sys_common/once/mod.rs')
| -rw-r--r-- | library/std/src/sys_common/once/mod.rs | 27 |
1 files changed, 9 insertions, 18 deletions
diff --git a/library/std/src/sys_common/once/mod.rs b/library/std/src/sys_common/once/mod.rs index 8742e68cc..359697d83 100644 --- a/library/std/src/sys_common/once/mod.rs +++ b/library/std/src/sys_common/once/mod.rs @@ -6,22 +6,6 @@ // 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. -// -// So to recap, the guarantees of a Once are that it will call the -// initialization closure at most once, and it will never return until the one -// that's running has finished running. This means that we need some form of -// blocking here while the custom callback is running at the very least. -// Additionally, we add on the restriction of **poisoning**. Whenever an -// initialization closure panics, the Once enters a "poisoned" state which means -// that all future calls will immediately panic as well. -// -// So to implement this, one might first reach for a `Mutex`, but those cannot -// be put into a `static`. It also gets a lot harder with poisoning to figure -// out when the mutex needs to be deallocated because it's not after the closure -// finishes, but after the first successful closure finishes. -// -// All in all, this is instead implemented with atomics and lock-free -// operations! Whee! cfg_if::cfg_if! { if #[cfg(any( @@ -36,8 +20,15 @@ cfg_if::cfg_if! { ))] { 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 { - mod generic; - pub use generic::{Once, OnceState}; + pub use crate::sys::once::{Once, OnceState}; } } |