[][src]Struct sgx_tstd::sync::Once

pub struct Once { /* fields omitted */ }

A synchronization primitive which can be used to run a one-time global initialization. Useful for one-time initialization for FFI or related functionality. This type can only be constructed with the Once::new constructor.


impl Once[src]

pub const fn new() -> Once[src]

Creates a new Once value.

pub fn call_once<F>(&self, f: F) where
    F: FnOnce(), 

Performs an initialization routine once and only once. The given closure will be executed if this is the first time call_once has been called, and otherwise the routine will not be invoked.

This method will block the calling thread if another initialization routine is currently running.

When this function returns, it is guaranteed that some initialization 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 threads at this point (there is a happens-before relation between the closure and code executing after the return).

If the given closure recursively invokes call_once on the same Once instance the exact behavior is not specified, allowed outcomes are a panic or a deadlock.


The closure f will only be executed once if this is called concurrently amongst many threads. If that closure panics, however, then it will poison this Once instance, causing all future invocations of call_once to also panic.

This is similar to poisoning with mutexes.

pub fn call_once_force<F>(&self, f: F) where
    F: FnOnce(&OnceState), 

Performs the same function as call_once except ignores poisoning.

Unlike call_once, if this Once has been poisoned (i.e., a previous call to call_once or call_once_force caused a panic), calling call_once_force will still invoke the closure f and will not result in an immediate panic. If f panics, the Once will remain in a poison state. If f does not panic, the Once will no longer be in a poison state and all future calls to call_once or call_one_force will be no-ops.

The closure f is yielded a OnceState structure which can be used to query the poison status of the Once.

pub fn is_completed(&self) -> bool[src]

Returns true if some call_once call has completed successfully. Specifically, is_completed will return false in the following situations:

  • call_once was not called at all,
  • call_once was called, but has not yet completed,
  • the Once instance is poisoned

This function returning false does not mean that Once has not been executed. For example, it may have been executed in the time between when is_completed starts executing and when it returns, in which case the false return value would be stale (but still permissible). call_once.

Trait Implementations

impl Debug for Once[src]

impl Send for Once[src]

impl Sync for Once[src]

Auto Trait Implementations

impl !RefUnwindSafe for Once

impl Unpin for Once

impl !UnwindSafe for Once

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.