Struct spin::once::Once [−][src]
once
only.Expand description
A primitive that provides lazy one-time initialization.
Unlike its std::sync
equivalent, this is generalized such that the closure returns a
value to be stored by the Once
(std::sync::Once
can be trivially emulated with
Once
).
Because Once::new
is const
, this primitive may be used to safely initialize statics.
Examples
use spin; static START: spin::Once = spin::Once::new(); START.call_once(|| { // run initialization here });
Implementations
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). The returned pointer will point to the result from the closure that was run.
Panics
This function will panic if the Once
previously panicked while attempting
to initialize. This is similar to the poisoning behaviour of std::sync
’s
primitives.
Examples
use spin; static INIT: spin::Once<usize> = spin::Once::new(); fn get_cached_val() -> usize { *INIT.call_once(expensive_computation) } fn expensive_computation() -> usize { // ... }
Spins until the Once
contains a value.
Note that in releases prior to 0.7
, this function had the behaviour of Once::poll
.
Panics
This function will panic if the Once
previously panicked while attempting
to initialize. This is similar to the poisoning behaviour of std::sync
’s
primitives.
Like Once::get
, but will spin if the Once
is in the process of being
initialized. If initialization has not even begun, None
will be returned.
Note that in releases prior to 0.7
, this function was named wait
.
Panics
This function will panic if the Once
previously panicked while attempting
to initialize. This is similar to the poisoning behaviour of std::sync
’s
primitives.
Creates a new initialized Once
.
Retrieve a pointer to the inner data.
While this method itself is safe, accessing the pointer before the Once
has been
initialized is UB, unless this method has already been written to from a pointer coming
from this method.
Returns a reference to the inner value if the Once
has been initialized.
Returns a reference to the inner value on the unchecked assumption that the Once
has been initialized.
Safety
This is extremely unsafe if the Once
has not already been initialized because a reference to uninitialized
memory will be returned, immediately triggering undefined behaviour (even if the reference goes unused).
However, this can be useful in some instances for exposing the Once
to FFI or when the overhead of atomically
checking initialization is unacceptable and the Once
has already been initialized.
Checks whether the value has been initialized.
This is done using Acquire
ordering, and
therefore it is safe to access the value directly via
get_unchecked
if this returns true.
Trait Implementations
Auto Trait Implementations
impl<T = (), R = Spin> !RefUnwindSafe for Once<T, R>
impl<T, R> UnwindSafe for Once<T, R> where
R: UnwindSafe,
T: UnwindSafe,