limit the number of retries of the busy handler #963
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MarinPostma
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LucioFranco
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Jan 30, 2024
| let mut maybe_state_slot = self.state.slot.write(); | ||
| // We need to make sure that the state slot is our slot before removing it. | ||
| if let Some(ref state_slot) = *maybe_state_slot { | ||
| if Arc::ptr_eq(state_slot, &old_slot) { |
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is there a case where a pointer gets reused and we run into a ABA problem?
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no, we discussed that last time, but we're actually comparing the pointer with itself, and we're still holding a reference to both ends while comparing, so no risk of it being reused in the meantime :)
LucioFranco
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haaawk
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| // We check that slot wasn't already stolen, and that their is still a slot. | ||
| // The ordering is relaxed because the atomic is only set under the slot lock. |
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This comment can probably go away, no?
haaawk
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Jan 31, 2024
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| if !*is_stolen { | ||
| lock.rollback(); | ||
| } | ||
| *is_stolen = true; |
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Shouldn't this be in opposite order?
let stolen = *is_stolen
*is_stolen = true;
if !stolen {
lock.rollback();
}
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no, think of it as "if not already stolen, then rollback, then mark as stolen"
haaawk
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psarna
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LucioFranco
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* limit the amount of retries for the lock stealer * use mutex for `is_stolen` * unconditionally update state after execute * shorten watch channel borrow * fmt
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This PR fixes a series of bugs that caused hangs on the platform.
is_stolenAtomicBoolby aMutex<bool>. I'm not sure this one was necessary, but I was desperate.borrow_and_updatein a channel was borrowing too long, causing a dead_lock. This was caused by some obscure rules about temporaries, causing the reference to be dropped after the call, even though it was being dereferenced. This is best exemplified by https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3c7bf7fbc2471c9bce121c781ebc982b, and elements of explanation can be found here: https://blog.m-ou.se/super-let/