sync: Introduce the SetOnce struct
#7418
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SetOnce struct
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The `SetOnce` data structure allows you to contain a T value and wait until the initialization of that T value in the Cell. It can only be initialized once and can be destroyed using `into_inner` or by dropping it. This is equivalent to the `asyncioEvent` class https://docs.python.org/3/library/asyncio-sync.html#asyncio.Event` The wait() allows you to block on a future which wakes up when the `SetOnce` is initalized. Added tokio/tests/sync_set_once.rs
…ingError Document each unsafe usage with safety commit and include reasoning
Use a mutex to ensure only one caller of `set` at a time. Change `wait()` to call `get_wait()` and panic if none Add `get_wait()` which waits until the value is set and checks the state again and returns None if the state is still not Set.
Lock mutex inside `wait()` when checking value_set, we also call `self.initialized()` after locking the mutex. We also add custom error type for SetOnce called SetError
Update a doc comment Remove &mut reference we don't need it
Remove some trailling space too so rustfmt doesn't complain
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Corrects the pull request reference from tokio-rs#7148 to tokio-rs#7418 in the tokio changelog entry.
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The link to Python's asyncio.Event documentation was pointing to asyncio-event.html which doesn't exist. This corrects it to the proper URL at asyncio-sync.html#asyncio.Event as mentioned in PR tokio-rs#7418.
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The
SetOncedata structure allows you to contain a T value and wait until the initialization of that T value in the Cell. It can only be initialized once and can be destroyed usinginto_inneror by dropping it.The wait() allows you to block on a future which wakes up when the
SetOnceis initalizedMotivation
After #7161 failed and was messy, we needed a new type that is like OnceCell but with tigter restrictions around T
Something similar in async_io in python https://docs.python.org/3/library/asyncio-sync.html#asyncio.Event
Solution
Proposal of the implementation of
SetOncedata structure.