coverage test is flaky recently

[yihau]

Problem

I can reproduce the error by cargo test -p solana-runtime and it is intermittent. would like to share some investigation here.

https://github.com/solana-labs/solana/blob/master/runtime/src/prioritization_fee_cache.rs#L482-L487

            let fee = PrioritizationFeeCache::get_prioritization_fee(
                prioritization_fee_cache.cache.clone(),
                &slot,
            );
            let fee = fee.lock().unwrap();
            assert_eq!(2, fee.get_min_transaction_fee().unwrap()); <--- die here

If I'm correct, prioritization_fee_cache.cache is updated by a function called service_loop. The function lives in another thread. If we do get_prioritization_fee via prioritization_fee_cache.cache before service_loop, we will get a default object. When we try to call get_min_transaction_fee from the default object, I think we will get a None.

Proposed Solution

maybe ensure the cache has been updated. not sure is there any determine way to do it.

cc @taozhu-chicago @willhickey @CriesofCarrots

[yihau]

seems Tao has fixed it. #27572

[tao-stones]

seems Tao has fixed it. #27572

Thanks for confirming the issue. I thought I updated all tests to call sync_update() to ensure cache's updated before asserting. But apparently i missed this one.

[tao-stones]

While looking into it, I also noticed that prioritization_fee_cache::drop() isn't necessary, if we are OK with not calling join() explicitly. As in #27568. wdyt @willhickey @CriesofCarrots