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Asynchronous values.
§Base Futures Concurrency
Often it’s desirable to await multiple futures as if it was a single
future. The join family of operations converts multiple futures into a
single future that returns all of their outputs. The race family of
operations converts multiple future into a single future that returns the
first output.
For operating on futures the following functions can be used:
| Name | Return signature | When does it return? |
|---|---|---|
Future::join | (T1, T2) | Wait for all to complete |
Future::race | T | Return on first value |
§Fallible Futures Concurrency
For operating on futures that return Result additional try_ variants of
the functions mentioned before can be used. These functions are aware of Result,
and will behave slightly differently from their base variants.
In the case of try_join, if any of the futures returns Err all
futures are dropped and an error is returned. This is referred to as
“short-circuiting”.
In the case of try_race, instead of returning the first future that
completes it returns the first future that successfully completes. This
means try_race will keep going until any one of the futures returns
Ok, or all futures have returned Err.
However sometimes it can be useful to use the base variants of the functions
even on futures that return Result. Here is an overview of operations that
work on Result, and their respective semantics:
| Name | Return signature | When does it return? |
|---|---|---|
Future::join | (Result<T, E>, Result<T, E>) | Wait for all to complete |
Future::try_join | Result<(T1, T2), E> | Return on first Err, wait for all to complete |
Future::race | Result<T, E> | Return on first value |
Future::try_race | Result<T, E> | Return on first Ok, reject on last Err |
Structs§
- An error returned when a future times out.
Traits§
- A future represents an asynchronous computation obtained by use of
async.
Functions§
- Never resolves to a value.
- Creates a new future wrapping around a function returning
Poll. - Resolves to the provided value.
- Awaits a future or times out after a duration of time.