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rt: add Handle::block_on #3549

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rt: add Handle::block_on #3549

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12 changes: 12 additions & 0 deletions tokio/src/runtime/handle.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,18 @@ impl Handle {
let _ = self.blocking_spawner.spawn(task, &self);
handle
}

/// TODO: write docs if this is a good direction
pub fn block_on<F: Future>(&self, future: F) -> F::Output {
// Enter the **runtime** context. This configures spawning, the current I/O driver, ...
let _rt_enter = self.enter();
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can enter check if the runtime is still alive?

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I think you opened a different issue, but that is someone of an orthogonal concern :)


// Enter a **blocking** context. This prevents blocking from a runtime.
let mut _blocking_enter = crate::runtime::enter(true);

// Block on the future
_blocking_enter.block_on(future).expect("failed to park thread")
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Then this should be a block on that runs the task and can wake up on runtime shutdown. We likely wanna use the same notify trick?

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The future isn't a task per se. When the runtime is shutdown, in theory all resources should transition to a "shutdown" state and in-flight operations canceled. This would result in this block_on waking up.

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Even if the task is doing nothing? E.g. if I just call handle.block_on(std::future::pending()), then what?

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Hmm, I guess my gut is that calling Handle::block_on shouldn't necessarily force exit when the runtime shuts down. My gut reaction is that handle.block_on(std::future::pending()) would just run indefinitely.

}
}

/// Error returned by `try_current` when no Runtime has been started
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