pub struct OnceLock<T> { /* private fields */ }
Expand description
A synchronization primitive which can be written to only once.
This type is a thread-safe OnceCell
.
Implementations
sourceimpl<T> OnceLock<T>
impl<T> OnceLock<T>
sourcepub fn get(&self) -> Option<&T>
pub fn get(&self) -> Option<&T>
Gets the reference to the underlying value.
Returns None
if the cell is empty, or being initialized. This
method never blocks.
sourcepub fn get_mut(&mut self) -> Option<&mut T>
pub fn get_mut(&mut self) -> Option<&mut T>
Gets the mutable reference to the underlying value.
Returns None
if the cell is empty. This method never blocks.
sourcepub fn set(&self, value: T) -> Result<(), T>
pub fn set(&self, value: T) -> Result<(), T>
Sets the contents of this cell to value
.
May block if another thread is currently attempting to initialize the cell. The cell is guaranteed to contain a value when set returns, though not necessarily the one provided.
Returns Ok(())
if the cell’s value was set by this call.
sourcepub fn get_or_init<F>(&self, f: F) -> &Twhere
F: FnOnce() -> T,
pub fn get_or_init<F>(&self, f: F) -> &Twhere
F: FnOnce() -> T,
Gets the contents of the cell, initializing it with f
if the cell
was empty.
Many threads may call get_or_init
concurrently with different
initializing functions, but it is guaranteed that only one function
will be executed.
Panics
If f
panics, the panic is propagated to the caller, and the cell
remains uninitialized.
It is an error to reentrantly initialize the cell from f
. The
exact outcome is unspecified. Current implementation deadlocks, but
this may be changed to a panic in the future.
sourcepub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>where
F: FnOnce() -> Result<T, E>,
pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>where
F: FnOnce() -> Result<T, E>,
Gets the contents of the cell, initializing it with f
if
the cell was empty. If the cell was empty and f
failed, an
error is returned.
Panics
If f
panics, the panic is propagated to the caller, and
the cell remains uninitialized.
It is an error to reentrantly initialize the cell from f
.
The exact outcome is unspecified. Current implementation
deadlocks, but this may be changed to a panic in the future.
sourcepub fn into_inner(self) -> Option<T>
pub fn into_inner(self) -> Option<T>
Consumes the OnceLock
, returning the wrapped value. Returns
None
if the cell was empty.