Struct OnceAsync 

pub(crate) struct OnceAsync<T> {
    fut: Mutex<Option<SharedResult<OnceFut<T>>>>,
}

A OnceAsync runs an async closure once, where multiple calls to OnceAsync::try_once return a OnceFut that resolves to the result of the same computation.

This is useful for joins where the results of one child are needed to proceed with multiple output stream

For example, in a hash join, one input is buffered and shared across potentially multiple output partitions. Each output partition must wait for the hash table to be built before proceeding.

Each output partition waits on the same OnceAsync before proceeding.

Fields

fut: Mutex<Option<SharedResult<OnceFut<T>>>>

Implementations

impl<T: 'static> OnceAsync<T>

pub(crate) fn try_once<F, Fut>(&self, f: F) -> Result<OnceFut<T>>

where F: FnOnce() -> Result<Fut>, Fut: Future<Output = Result<T>> + Send + 'static,

If this is the first call to this function on this object, will invoke f to obtain a future and return a OnceFut referring to this. f may fail, in which case its error is returned.

If this is not the first call, will return a OnceFut referring to the same future as was returned by the first call - or the same error if the initial call to f failed.

Trait Implementations

impl<T> Debug for OnceAsync<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Default for OnceAsync<T>

fn default() -> Self

Returns the “default value” for a type.